4

Methods and Effects of Fertility Management

This chapter reviews and assesses current options for controlling fertility of free-ranging horses and burros. Investigation of potential fertility-control options was one of the mandates of the previous National Research Council studies. In the late 1970s and early 1980s, the Committee on Wild and Free-Roaming Horses and Burros reviewed the status of contraception, including sterilization, for population control in free-ranging herds. That committee reported on the feasibility of several techniques, including hormone injections for stallions and hormone treatments, intrauterine devices (IUDs), and surgery for mares. It concluded that endocrine contraception in stallions or mares was the most promising approach because IUDs often dislodged and surgery was impractical in field conditions (NRC, 1980). The 1980 report noted that studies of endocrine contraception in stallions were going on at the time and recommended a study of contraception in mares. In 1991, the Committee on Wild Horse and Burro Research reviewed the proposal for and later the results of a study that examined steroid implants in mares captured from the range and held in pens, steroid implants in free-ranging mares, and vasectomies of free-ranging dominant stallions. That committee found some steroid treatments to be effective in mares. Vasectomies were effective in sterilizing individual animals, but the committee questioned the technique’s effectiveness at a population level, given that only dominant stallions were treated (NRC, 1991).

Research on effective methods of fertility control remains important to the Bureau of Land Management (BLM) because fertility control is the major alternative to gathering and removing horses that is generally accepted by the public. In the 20 years since the last National Research Council report was completed, considerable progress has been made in developing and testing fertility control for wild animal populations, both free-ranging and captive. Research with captive animals has been especially valuable in allowing more extensive and careful monitoring and analysis of efficacy and safety of a wide array of products. In particular, pathological conditions associated with some types of contraceptive treatment have been detected and are under systematic investigation, which is difficult to accomplish in free-ranging populations.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 93
4 Methods and Effects of Fertility Management T his chapter reviews and assesses current options for controlling fertility of free- ranging horses and burros. Investigation of potential fertility-control options was one of the mandates of the previous National Research Council studies. In the late 1970s and early 1980s, the Committee on Wild and Free-Roaming Horses and Burros reviewed the status of contraception, including sterilization, for population control in free-ranging herds. That committee reported on the feasibility of several techniques, including hormone injections for stallions and hormone treatments, intrauterine devices (IUDs), and surgery for mares. It concluded that endocrine contraception in stallions or mares was the most promising approach because IUDs often dislodged and surgery was impractical in field conditions (NRC, 1980). The 1980 report noted that studies of endocrine contraception in stallions were going on at the time and recommended a study of contraception in mares. In 1991, the Committee on Wild Horse and Burro Research reviewed the proposal for and later the results of a study that examined steroid implants in mares captured from the range and held in pens, steroid implants in free-ranging mares, and vasectomies of free-ranging dominant stallions. That committee found some steroid treatments to be effective in mares. Vasectomies were effective in sterilizing individual animals, but the committee questioned the technique’s effectiveness at a population level, given that only dominant stallions were treated (NRC, 1991). Research on effective methods of fertility control remains important to the Bureau of Land Management (BLM) because fertility control is the major alternative to gathering and removing horses that is generally accepted by the public. In the 20 years since the last National Research Council report was completed, considerable progress has been made in developing and testing fertility control for wild animal populations, both free-ranging and captive. Research with captive animals has been especially valuable in allowing more extensive and careful monitoring and analysis of efficacy and safety of a wide array of products. In particular, pathological conditions associated with some types of contraceptive treatment have been detected and are under systematic investigation, which is difficult to accomplish in free-ranging populations. 93

OCR for page 93
94 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Although the committee’s report includes information on burros as well as horses, the need for fertility control in horses is considered more pressing because their populations are much larger (BLM, 2003, revised 2005). In addition, many more studies have focused on horses, so considerably more data are available on them than on burros. Nevertheless, given similarities in reproductive physiology, the efficacy and safety of methods could be expected to be generally similar in the two species. Their social structures differ, however, as described in the following sections, and this could influence the effects of fertility-control methods on behavior and social organization. Reversible contraception and permanent sterilization are achieved by interrupting re- productive processes, and the committee’s evaluation of these methods is based in part on understanding their effects on an animal’s reproductive physiology and behavior. Accord- ingly, this chapter starts with two reviews: one on equine social and mating behavior, social relationships, and social structure and a second on reproductive physiology in domestic horses and donkeys, with information on free-ranging horses and burros when available. The brief reviews are intended to serve as background for understanding the potential e ­ ffects of fertility-control methods on behavior and reproductive processes. The chapter then evaluates available fertility-control treatments for both females and males and sum- marizes the advantages and disadvantages of the most promising methods. EQUINE SOCIAL BEHAVIOR AND SOCIAL STRUCTURE Horses, zebras, and asses (the primogenitors of donkeys and burros) are highly social animals, but their social structures vary. Klingel (1975) was the first to document that equids exhibit two types of social organization. In one, typified by horses and plains and mountain zebras, females and their young live in closed membership groups with one, and occasion- ally a second, male. In those so-called harem groups, females benefit by receiving material rewards from their males (Rubenstein, 1986). Enhanced male vigilance against potential intruder males not only reduces a male’s chances of being cuckolded but reduces harass- ment experienced by females. Consequently, females can devote more time to feeding and increase the likelihood that their offspring will survive to independence (Rubenstein, 1986). That type of society emerges under more mesic environmental conditions in which food is relatively abundant and distributed near predictable watering points. In more arid areas, where abundant food is far from water, the second type of society appears, as typified by Grevy’s zebras and the wild asses, including the African wild ass that is the ancestor of the donkey. Arid and semiarid conditions make it difficult for females, whether with or without young foals, to remain together in closed-membership groups, meet their different physiological needs, and benefit from the extra foraging time that heightened male vigilance provides. Nonlactating females and mares that have older foals need drink only every 3-5 days (Ginsberg, 1989; Becker and Ginsberg, 1990), whereas ones that have foals 3 months old and younger must drink daily. The latter females stay near water whereas the others wander more widely in search of better pasture. Because both types of females are fertile and males cannot be with both simultaneously, males establish territories. The most dominant hold areas near water, where they have exclusive access to females that have young foals and intercept those coming to water every few days. Aridity thus alters the nature of relationships among both females and males and leads to a more fluid, fission-fusion type of social system (Rubenstein, 1994). Although the two social systems emerge from differences in individual social relation- ships and environmental conditions, they share some important characteristics. First, the mother-infant bond is strong in all equids. Second, sons and daughters leave their mothers

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 95 when they reach sexual maturity; males join bachelor groups, and females are immedi- ately integrated into adult society. Third, the female reproductive state influences female nutritional needs; meeting these needs sometimes permits long-term stable bonds to form but sometimes does not. Much depends on long-term evolutionary responses to ecological circumstances that lead to the emergence of different social systems. In free-ranging horses, the norm is a stable society in which females can meet their needs while benefiting from limited interruptions. In free-ranging burros, fluidity of social relationships is the norm in that close bonds among females and between males and females are precluded by the disjunctive nature of high-quality feeding and drinking locations. REPRODUCTION IN DOMESTIC HORSES AND DONKEYS This section provides an overview of the various points in the reproductive processes of male and female horses and burros that can be targeted for fertility control (see Asa, 2010, and Asa and Porton, 2010, for further details). Sexual maturity in free-ranging male and female horses occurs at the age of about 18 months, but onset of reproduction is dependent on social parameters within the popu- lation. First reproduction for males is typically delayed for up to several years while they reach social maturity. Sexual maturity in domestic donkeys and free-ranging burros is re- ported to occur at the age of 1-2 years in females (Fielding, 1988; Pugh, 2002) and 1.5 years in males (Nipken and Wrobel, 1997). The earliest possible age of puberty in males and females of both species is 1 year, so preventing reproduction in those animals would require that treatment begin before that age. Both species have seasonal breeding patterns, but seasonality is less pronounced in domestic donkeys and free-ranging burros (Ginther et al., 1987). Seasonal reproduction is controlled primarily by photoperiod, but temperature and body condition can also influ- ence reproductive timing (Sharp and Ginther, 1975; Guillaume et al., 2002). Thus, local conditions can affect the length of the breeding season, especially for female horses. Male domestic horses can produce sperm year round, but the quality declines during winter, the mares’ nonbreeding season (Pickett et al., 1975). Most female free-ranging horses give birth in the spring, and this is followed within 5-12 days by postpartum estrus (foal heat), when conception is again possible. Female d ­ omestic donkeys also show postpartum estrus (Pugh, 2002). Nonpregnant female domes- tic donkeys also begin to have reproductive cycles in the spring, and domestic horses and donkeys both continue cycling until conception or the end of the breeding season. For horses and donkeys, as for many other mammals, the ovarian or estrous cycle is divided into phases. During the follicular or estrous phase (when females will stand for mating), follicle growth is stimulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus and follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary. The follicles produce estradiol, which stimulates estrous behavior. The estrous phase in donkeys and horses reportedly lasts about 6-9 days (Ginther, 1979; Vandeplassche et al., 1981). During estrus, the female is attractive to males and receptive to mating. Courtship behaviors are generally similar in horses and donkeys with some important exceptions. Estrous horses often raise their tails, exposing the genital area, as they approach and ­ ollow f males (Asa, 1986). Tail raise is not as obvious in female donkeys, but they spend more time in proximity to males and respond to male vocalization by approaching (Henry et al., 1991). Courtship interactions tend to be more vigorous in donkeys and include more ele- ments of aggression, such as kicking and chasing. Female horses urinate more frequently

OCR for page 93
96 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM during estrus, and males assess urine via the flehmen response, which introduces phero- mones into the vomeronasal organ for neural processing of the female’s reproductive status (Stahlbaum and Houpt, 1989). Vocalization appears to be more important in donkeys, males of which commonly initiate sexual interactions by vocalizing (Henry et al., 1991). Ovulation occurs toward the end of the estrous phase, but courtship and mating may continue for an additional couple of days in both horses and donkeys. An LH surge trig- gers ovulation, which is followed by conversion of the follicles to corpora lutea (CL), which produce progesterone. Progesterone domination during the luteal phase, also called d ­ iestrus, inhibits further estrous behavior. The total cycle in horses lasts about 3 weeks but in ­ onkeys may last as long as 28 days (Ginther, 1979; Vandeplassche et al., 1981; Fielding, d 1988). ­ stradiol and progesterone prepare the uterus for implantation and nourishing the E embryo. Fertility rates in domestic horses are reported to range from about 80 to 100 percent per breeding season, depending on factors such as breed, age, and reproductive history (re- viewed in Ginther, 1979). Fertility rates are lower in older and very young mares (Carnevale and Ginther, 1992; Vanderwall et al., 1993). Rates are also lower in domestic mares that have not previously foaled than in currently lactating mares (reviewed in Ginther, 1979). In one study of pasture breeding of domestic donkeys, all 14 females that were examined were pregnant (Henry et al., 1991). Gestation length is 11 months in horses and 12-12.5 months in domestic donkeys (Ginther, 1979; Fielding, 1988). However, possible ovulation or spontaneous luteinization, resulting in the formation of secondary CL, around day 40 can confound calculation of ges- tation length in field studies. Estradiol secreted by the follicles that precede CL formation can stimulate estrous behavior in a small percentage of pregnant females (Tomasgard and Benjaminsen, 1975) and give the appearance of a natural estrous cycle. With a gestation length of about a year, horses and donkeys can give birth every year. However, that may not occur, especially in nutritionally stressed females. In particular, nursing females, experiencing the energetic drain of lactation in addition to maintenance, may not succeed in sustaining a pregnancy. But lactation itself does not prevent estrous cycles, so conception may occur, although the embryo may be lost if the female is nutrition- ally stressed. Early embryo loss (defined as up to day 40 of pregnancy) is reported to be 5-15 percent even in well-fed domestic mares but can be 30 percent or higher in mares that are 18 years old or older (Vanderwall, 2008). Pregnancy loss may also be high in yearling mares (Mitchell and Allen, 1975). In a small study of domestic donkeys, three of 14 pregnant females experienced early embryo loss (Henry et al., 1991). POTENTIAL METHODS OF FERTILITY CONTROL IN FREE-RANGING HORSES AND BURROS First, it is important to note that, when the committee prepared its report, no fertility- control methods that were highly effective, easily delivered, and affordable were avail- able for use across all BLM Herd Management Areas (HMAs). In addition, there were no fertility-control methods that did not alter the behavior or physiology of free-ranging horses and burros in some way. Any method that prevents reproduction can do so only by affecting some aspect of the reproductive system. Even if the only effect were to prevent births, that would change the age structure of a herd by reducing the number of young and could enhance the health of females by reducing the caloric demands of reproduction. Thus, in evaluating fertility-control methods, it is important to compare them not only for obvious factors—such as efficacy, mode of delivery, and cost—but for the constellation of

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 97 their effects on physiology, behavior, and social structure. It is also critical to extend the comparisons to the social-structure changes and behavioral and health effects that are caused by gathers. The porcine zona pellucida (PZP) vaccine, an immunocontraceptive, is the most exten- sively tested method in free-ranging horses and may be the most promising option at pres- ent. Several other methods that are potentially useful in horse and burro populations will be considered in this chapter, but more research may be required before their application can be recommended. Fertility-control methods range from other types of vaccines to hormone agonists;1 some methods are more appropriate for treatment of females, and ­ thers could o be used to control male fertility. Some of the methods are reversible—and ­ llow the pos- a sibility of future restoration of fertility—but others are permanent sterilants that have the economic and logistical advantage of making repeated treatment unnecessary. In particular, nonsurgical approaches to sterilization will be evaluated. Methods that are not considered permanent may not be 100-percent reversible in all animals. Even if a contraceptive, such as an implant, is removed or its effect wears off (in the case of an injectable contraceptive), other factors may slow or even prevent complete restoration of fertility. Many factors affect fertility and time to conception or birth even in females that have never been treated with contraceptives (reviewed in Asa, 2005). Female age is the most obvious factor, but parity (the number of times that a female has given birth), age at production of first offspring, time elapsed since last pregnancy, nutritional status, health, genetics, and other more subtle factors can also influence a female’s ability to con- ceive and maintain a pregnancy to term. Fertility of previously contracepted females can be affected by those factors and by lingering effects of the contraceptive itself. Individual differences are common. The process of selecting the best method for the species and situation includes an evaluation of many equally important factors, such as delivery route, efficacy, duration of effect or reversibility, physiological side effects, and possible effects on behavior and social structure. It is also important to know whether a method is safe for prepubertal animals and whether females can be treated during pregnancy or lactation. Although methods can be male- or female-directed, more research in control of fertility in free-ranging equids has targeted females, specifically different formulations of the PZP vaccine, than males. The following review includes methods for both males and females and methods that have been tested with other species that could be considered for use in free-ranging equids. ADJUSTMENT OF SEX RATIO TO LIMIT REPRODUCTIVE RATES Adjustment of the sex ratio to favor males has been proposed for managing popula- tion growth rates of horse and burro populations. Sex ratio typically is somewhat adjusted after a gather in such a way that 60 percent of the horses returned to the range are male. At that ratio, however, population growth would be only slightly reduced: modeling by Bartholow (2004) suggests that birth rates could decline from about 20 percent to 15 percent a year if the proportion of males increased from 0.50 to 0.57. If more aggressive sex-ratio adjustments are initiated by drastically altering the number of females relative to males beyond a 40:60 ratio, care should be taken to assess possible additional consequences. In the Pryor Mountain Wild Horse Range, Singer and Schoeneker (2000) found that increases in the number of males on this HMA lowered the breeding male age but did not alter the birth rate. Because the existing females were distributed among many more small harems, 1  hormone A agonist binds to a receptor of a cell and has the same action as the native hormone.

OCR for page 93
98 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM estimates of genetic effective population size increased.2 In addition, bachelor males will likely continue to seek matings, thus increasing the overall level of male-male aggression (Rubenstein, 1986). Male condition may decline because of the increase in time spent in competing, and the disruption caused by male-male competition may affect female forag- ing success. Both those outcomes might reduce overall population growth more than would a reduction in the number of breeding females. Because horses and burros have polygynous mating systems (multiple females mate with one male), additional males would not be expected to affect the likelihood of reproduction in individual females. Reduction in repro- ductive rate would depend on the number of females remaining. Having a larger number of males competing could favor females by enhancing the opportunities for mate choice, could mean that males of higher genetic quality would achieve harem stallion status, or both. Given that the addition of males or the subtraction of females can lead to a similar sex ratio but have different effects on population growth rates, forecasting models tuned with population-specific survival and fecundity levels can be used to determine how to adjust sex ratios to limit population growth in individual populations effectively. FEMALE-DIRECTED METHODS OF FERTILITY CONTROL Potential methods of fertility control directed at female equids include surgical o ­ variectomy (removal of the ovaries); immunocontraceptives, which trigger the animal’s immune system to prevent pregnancy; GnRH agonists; steroid hormones; and intrauterine devices. The mode of action and effects of each method are reviewed below. Surgical Ovariectomy Surgical ovariectomy and ovariohysterectomy are commonly used in domestic ­ pecies, s such as cats and dogs (including feral cats and dogs), but seldom applied to other free-­ anging r species. Accessing the female reproductive tract, which lies within the body cavity, in con- ­ trast with the reproductive tract of males of most species, which have external testes, ­ arries c the risk of dehiscence of sutures or infection. However, an alternative vaginal approach, ­ c ­ olpotomy, avoids an external incision and reduces the chances of surgical complications or infection (Rodgerson and Loesch, 2011). The mare is sedated and tranquilized while stand- ing but restrained; a local anesthetic is sometimes used as well to reduce movement during surgery. An incision is made through the wall of the vagina and then through the perito- neum to access the ovaries. Although the risks are lower than with trans­ bdominal surgery, a ­episioplasty (suturing to close the vulva) and stall restriction for 2-7 days are recommended to reduce the chance of evisceration. Monitoring for 24-48 hours for signs of hypovolemic shock due to internal bleeding is also recommended. The procedure is not without risk. Duration and Efficacy Removal of the ovaries is of course permanent and 100-percent effective. ­ variectomy O during the first 2-3 months of pregnancy results in abortion because of the loss of progesterone 2  Effective population size is the size of an idealized population that would experience the same magnitude of random genetic drift as the population of interest. Populations that have experienced fluctuating sizes between generations, unequal sex ratios, or high variance in reproductive success are likely to have effective population sizes that are lower than the number of animals present. The concept of effective population size is discussed in Chapter 5.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 99 from the corpus luteum (Holtan et al., 1979). Ovariectomy during the period of lactation would not be expected to affect milk production, inasmuch as gonadal hormones (estrogen and progesterone) are important during late pregnancy when mammary glands are devel- oping but not after milk production is established. Side Effects Typical side effects associated with ovariectomy in many species include decreased activity and weight gain. The absence of gonadal hormones could affect sociosexual behav- ior but perhaps not as profoundly as in most other species. Although the cyclic production of estrogen by the ovaries is required for stimulation of estrus and mating behavior in virtually all species, the horse is an exception. The full repertoire of courtship and mating behavior has been displayed by ovariectomized mares and by anestrous mares during the nonbreeding season (Asa et al., 1980b; Hooper et al., 1993). The behavior was found to be hormonally supported by adrenal sex steroids (Asa et al., 1980a), for example, estrone and dehydroepiandrosterone, a weak estrogen and an androgen, respectively. In contrast with ovarian hormones, adrenal sex steroids are not secreted cyclically, so estrous behavior is displayed sporadically. No comparable study of the sexual behavior of free-ranging, nonpregnant mares has been conducted during the nonbreeding season. However, if free- ranging ovariectomized mares also show estrous behavior and occasionally allow copula- tion, interest of the stallion would be maintained, and this would foster band cohesion. Immunocontraceptives No other class of contraceptives has been as extensively researched in domestic and free-ranging equids as immunocontraceptives. Immunocontraception relies on the target species’ immune system to produce an immune reaction (usually in the form of antibodies) to some target tissue or biochemical that is required for successful reproduction. The im- mune response is most often triggered by inoculation of the target species with bio­chemicals or tissues from other species that are similar in structure to the biochemicals or tissues of the host. The target animal’s immune system responds to the foreign compounds injected into the body by producing antibodies that bind to both the injected, foreign compounds and the structurally similar tissues or biochemicals in the target species. The biological ef- fects of the immunocontraceptive, aside from prevention of conception, depend on which biochemicals or tissues are the intended targets, the ability of the immunocontraceptive to induce an immune response (its immunogenicity), the specificity of the immune response to the target biochemicals or tissues, and the duration of the immune response. In equids, the two most studied immunocontraceptives are vaccines directed against GnRH, a peptide hormone produced by the hypothalamus, and the zona pellucida, the outer membrane layer surrounding the mammalian oocyte (egg). Both are discussed below in further detail with regard to delivery routes, efficacy, duration of effect or reversibility, and side effects. This review focuses on published studies of captive and free-ranging horses, where available; otherwise, results from studies of other ungulates are used to provide an approximation of what might occur after application of the treatment to horses. Porcine Zona Pellucida Vaccine Sperm must bind to the zona pellucida of the oocyte to initiate the sperm acrosome reaction that is required for fertilization. Anti-zona pellucida vaccines prevent conception

OCR for page 93
100 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Normal Egg Contraceptive Fertilization Effect on Egg Anti-Zona Sperm Antibody Receptor Sperm Binds to Zona Pellucida Receptor Zona Pellucida Horse Egg Sperm Blocked from Binding by Anti-Zona Pellucida Antibody FIGURE 4-1  Mode of action of porcine zona pellucida vaccine. SOURCE: Illustration provided by I.K.M. Liu. late in the chain of events required for successful fertilization by preventing sperm from fertilizing eggs (Figure 4-1). There are three formulations of the PZP vaccine: a liquid for- mulation accompanied by a primer that is effective for 1 year (liquid PZP), a time-release pellet formulation that can be effective for up to 22 months (PZP-22), and a formulation in which PZP is encapsulated in liposomes3 to extend contraception efficacy (SpayVac®; Immuno­ accine Technologies, Inc. [IMV], Halifax, Canada). v figure one.eps It is important to note that PZP vaccines are not a homogeneous set of compounds. The term liquid PZP used below refers to a PZP vaccine prepared according to the methods originally outlined for the horse by Liu et al. (1989) in which pig ovaries are finely sliced to release oocytes from surrounding tissues. The PZP in SpayVac is different in two ways. First, it is prepared differently: whole ovaries are ground and homogenized to separate oocytes from tissues (Yurewicz et al., 1983). Second, the PZP is encapsulated in liposomes to extend the period of release (Brown et al., 1997). In both procedures, the product passes through a series of filters of decreasing pore size to remove other ovarian debris, but it is possible that the SpayVac preparation contains more non-zona pellucida ovarian proteins than liquid PZP produced with the Liu et al. method. Ovarian proteins cannot reliably be separated from zona pellucida proteins by filtration, and the initial grinding and homog- enization of whole ovaries in the Yurewicz et al. method results in more non-zona pellu- cida debris in the initial suspension. Less pure products (containing more ovarian debris) may be more immunogenic than zona pellucida proteins alone and enhance the immune response. Miller et al. (2009) suggested that the difference in antigen preparation might ex- plain the longer duration of efficacy in their SpayVac-treated deer than in deer treated with liquid PZP, but more work is needed to determine whether antigen preparation methods 3  liposome is an artificially prepared vesicle composed of a lipid bilayer that can incorporate drugs for con- A trolled delivery.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 101 result in differences in PZP efficacy. Ovaries were not examined for pathological effects in horses, deer, or other species treated with SpayVac, nor were any long-term studies done on its reversibility. It is possible that SpayVac prevents fertilization by means in addition to or other than sperm blockage. Reversibility also requires further investigation. All published studies that have used SpayVac liposome preparations in free-ranging horses included the adjuvant AdjuVac™ prepared by Miller at the U.S. Department of Agriculture’s National Wildlife Research Center (NWRC). However, Miller has shown that liposomes are dis- solved by the lipid-based adjuvant AdjuVac, which would be expected to shorten its period of efficacy in that the liposomes were designed to prolong contraceptive effect (L. Miller, NWRC, personal communication). It is also important to note that over the years liquid PZP has been administered to horses with several treatment protocols for the first inoculation, and the effects of the dif- ferent protocols and of protocols for administering boosters are still not fully understood. For example, in the first study of liquid PZP in domestic mares, Liu et al. (1989) adminis- tered the vaccine in four initial injections at 2-week intervals, whereas much of the later work with PZP by Kirkpatrick, Turner, and colleagues (e.g., Kirkpatrick et al., 1991; Turner et al., 1997) involved two initial injections 4 weeks apart. Much of the more recent work (e.g., Liu et al., 2005; Turner et al., 2007) used single-injection protocols that appear to be more feasible in field settings. It is also unclear whether annual booster vaccinations with liquid PZP (e.g., Kirkpatrick et al., 1991) and timed-release PZP pellets (e.g., Turner et al., 2007) generate the same immunologic dynamics needed to prolong the effect of PZP. For example, the total amount of PZP released from a timed-release pellet during the boost period may differ from the amount of PZP in a liquid booster vaccination, and the dura- tion of exposure may not be equivalent. Furthermore, the immune system may respond to these alternative antigen presentations in different ways. The immunologic dynamics induced in the target species with different treatment and boosting protocols are not yet definitively understood. Delivery Route. Both the liquid and pellet formulations of PZP can be administered by hand to free-ranging equids that have been captured. Liquid PZP can be delivered by dart to animals in the field (Kirkpatrick et al., 1990). Pelleted PZP must be given by hand because darts cannot provide adequate pressure to release pellets into the animal effectively; this was verified in a study of pelleted PZP that was effective for 1 year: the efficacy of the hand- injected PZP was twice that of the dart-injected PZP (Turner et al., 2008). SpayVac (Brown et al., 1997) can be given by hand or dart. Although the ability to deliver liquid PZP via dart is a useful option, it is not clear how successful attempts would be to dart populations of horses at the desired level of treatment intensity, given the large number of animals needing treatment, variability in the tempera- ment of the horses, and the terrain of HMAs. Two studies of free-ranging horses and one of white-tailed deer have found that over time, with repeated boosters, the difficulty of approaching animals on foot for darting increased (Kirkpatrick and Turner, 2008; Rutberg and Naugle, 2008; Ransom et al., 2011). At the time the report was prepared, the most ef- fective and most reliable method of delivery was hand injection after a gather. However, alternative methods, such as trapping near water holes or blinds, have been used in other areas and could be useful in some HMAs. Efficacy. Liquid PZP, the first formulation produced, has been assessed for efficacy more often than other PZP formulations. The overall mean of published efficacy values in horses is 88.4 percent (median, 89 percent). Kirkpatrick and Turner’s (2008) value of 95 percent is

OCR for page 93
102 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM based on cumulative experience on Assateague Island4 and represents the most up-to-date information available to the committee on that site. Turner et al. (1997) evaluated several adjuvant formulations.5 If the less effective adjuvants in their study and another study that acknowledged poorly timed boosters in one population (Ransom et al., 2011) are eliminated, the mean efficacy increases to 91.5 percent (median, 90 percent), representing hundreds of animals across several sites. In most of the studies, efficacy was assessed by determining how many treated females had foals in the following foaling season or had pregnancy diagnosed with hormone assays. Only one study of any PZP formulation has been conducted in burros. Turner et al. (1996) found that liquid PZP significantly reduced fertility for a year after vaccination. A two-shot protocol was more effective (none of 13 females became pregnant) than a one-shot protocol (one of three became pregnant). Turner et al. (2007) assessed a pelleted form designed to release PZP into the animal’s circulatory system at 1, 3, and 12 months in 96 free-ranging mares in Nevada. Fertility rates over 4 years after vaccination were 5.2 percent, 14.9 percent, 31.6 percent, and 46.2 percent, respectively, in treated mares. The mean fertility rate of untreated females during the study was 53.8 percent. The formulation has come to be called PZP-22 because it remains about 85-percent effective after 22 months. Turner et al. (2008) concluded that the optimal time to administer PZP-22 for maximum duration of effect is fall or winter. BLM began using PZP- 22 in free-ranging horses in the late 2000s. However, the efficacy has varied as treatment has been extended to additional field sites. Foaling has been reduced by 30-79 percent in the 2 years after a single injection of PZP-22 at various field sites (J.W. Turner, University of Toledo, personal communication, November 2012). The variability is believed to be due to the time of year of injection, whether delivery was by dart or by hand, the location of the injection (the hip is considered ideal, but that is not always possible when delivery is by dart), and pos- sible differences in preparation in the field. In addition, there has been a change in vaccine production during the last few years: heat extrusion versus cold evaporation (J.W. Turner, University of Toledo, personal communication, November 2012). Only one published study (Killian et al., 2008a) has evaluated SpayVac efficacy in horses. In a study of captive horses in Nevada, 12 mares received a single hand injection in the neck of 400 µg of SpayVac emulsified with AdjuVac adjuvant for a total volume of 1 mL in March 2003. In fall of each year, treated mares were examined for pregnancy via ultrasonography or rectal palpation, and the observations were later verified by whether a foal was born. In a few cases in which a mare’s behavior prevented that kind of examina- tion, the birth of a foal (or the absence of a birth) in spring of the following year was used to assess fertility and treatment efficacy. In the 4 years of the study, contraception efficacy in the SpayVac-treated mares was 100 percent in year 1 and 83 percent in years 2-4. Bar- tell (2011) determined that SpayVac in combination with nonaqueous Freund’s modified adjuvant (FMA) induced the strongest immune response in domestic horses as measured by antibody titers and exhibited the strongest suppression of progesterone compared with an aqueous preparation of FMA and non–mycobacterium-based adjuvant, but she did not assess pregnancy or foaling. 4  Assateague Island National Seashore is on a barrier island off the coast of Maryland and operated by the U.S. Department of the Interior’s National Park Service (NPS). A free-ranging herd lives on the island. NPS is not sub- ject to the Wild Free-Roaming Horses and Burros Act of 1971. Nevertheless, because it is a free-ranging population, results of studies of the use of liquid PZP on this herd can inform management of horses under BLM’s jurisdiction. 5  An adjuvant enhances the immune response by encouraging the production of antibodies.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 103 SpayVac has also been evaluated in deer. Miller et al. (2009) evaluated SpayVac and liquid PZP in combination with different adjuvants in 30 captive white-tailed deer grouped into six treatment groups of five does each. SpayVac was administered in three prepara- tions: with liposomes in AdjuVac emulsion, lyophilized with liposomes in AdjuVac suspen- sion, and with liposomes in an alum adjuvant suspension. PZP was produced with two protocols (labeled IVT and NWRC for the providers of the antigen). The SpayVac/AdjuVac emulsion and the IVT-PZP/AdjuVac emulsion had the longest duration of effect: 80 percent of treated deer were contracepted for at least 5 years. Monitoring of the ­ payVac/AdjuVac S group ceased at 5 years; the IVT-PZP/AdjuVac continued to be effective for 7 years. The estimated decline in fecundity (fawns produced per female) was greater than 90 percent. All other formulations were inferior in performance. The authors concluded that AdjuVac is critical and should be used in emulsion form rather than suspension. They also sug- gested that, because of production differences, the IVT-PZP probably contained more por- cine ovarian tissue and was thus more effective. Fraker et al. (2002) evaluated the efficacy of SpayVac emulsified with Freund’s complete adjuvant (FCA) administered to 41 free-­ ranging fallow deer. Contraception of treated does was 100 percent over 3 years; however, the samples obtained in the 3 years were from different animals because some animals were culled for analysis. The authors suggested that, on the basis of the antibody titers present after 3 years, the SpayVac vaccination would probably continue to be effective for a longer period. Locke et al. (2007) evaluated SpayVac emulsified with AdjuVac over a 2-year period in wild white-tailed deer (34 treated, 11 controls) and found 100-percent efficacy in both fawning seasons. Killian et al. (2005) cited data from their studies of captive white-tailed deer in Pennsylvania that showed 80-percent efficacy in does for 4 years. Gray et al. (2010) evaluated a PZP vaccine that was mistakenly referred to as SpayVac (Fraker and Brown, 2011; Gray et al., 2011) in 20 treated and 18 untreated free-ranging mares in Nevada over a 3-year period. The liquid-PZP vaccine was prepared as SpayVac but without liposomes. Efficacy was lower (50-63 percent) than reported by Killian et al. (2008a) for SpayVac. Gray et al. (2010) suggested that the lower efficacy might have been due to their more conservative methods of assessing efficacy in the field; however, in a follow-up published erratum, they acknowledged that the vaccine formulation that they used lacked the liposome compounds included in the SpayVac vaccine (Gray et al., 2011) and suggested that this could explain the differing results. Thus, the studies by Gray et al. (2010) should not be compared to other results for SpayVac specifically, and it is not clear whether these results should be compared to those for liquid PZP. In both the Killian et al. (2008a) and Gray et al. (2010) studies, the AdjuVac adjuvant was combined with the vaccine. Reversibility. Immunocontraception depends on the immune response to the vaccine reach- ing and staying above threshold concentration (Adams and Adams, 1990; Zeng et al., 2002). Reversibility of the contraceptive effect depends on the reduction of circulating antibody titers. Substantial variability in reversal time is likely and can be due to the vaccine formula- tion, the adjuvant used, the treatment protocol, genetic factors, and the nutritional status of the individual animal because these factors may affect the initial and continuing immune response to the vaccine (Homsy et al., 1986; Chandra and Amorin, 1992; Turner et al., 1997, 2001, 2007; Liu et al., 2005; Lyda et al., 2005; Bartell, 2011). In the first study of liquid PZP in equids, Liu et al. (1989) found that, of 10 feral and six domestic mares, most mares had reversed within 8 months of treatment. Kirkpatrick et al. (1990) first demonstrated that three of seven free-ranging mares became fertile in the first year after 1 year of liquid-PZP treatment, although foaling rates of treated mares overall were lower after treatment than in control mares. Turner et al. (1997) found similar results

OCR for page 93
132 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM TABLE 4-1  Advantages and Disadvantages of the Most Promising Fertility-Control Methods Method Advantages Disadvantages PZP-22 and Research and application in both Capture needed for hand injection of PZP-22 SpayVac®a captive and free-ranging horses Allows estrous cycles to continue so Extended breeding season requires males to natural behaviors are maintained defend females longer High efficacy With repeated use, return to fertility becomes less predictable Can be administered during pregnancy Out-of-season births are possible or lactation Chemical Simpler than surgical vasectomy Requires handling and light anesthesia Vasectomy Permanent Permanent No side effects expected Only surgical vasectomy has been studied in horses, so side effects of the chemical agent are unknown Normal male behaviors maintained Extended breeding season requires males to defend females longer and may result in late- season foals if remaining fertile males mate Should have high efficacy Only surgical vasectomy has been studied in horses, so efficacy rate is unknown GonaCon™ Capture may be needed for hand injection of for Females initial vaccine and any boosters Effective for multiple years Lower efficacy than PZP-vaccine products, especially after first year Sexual behavior exhibited Sexual behavior may not be cyclic, inasmuch as ovulation appears to be blocked Social behaviors not affected in the Should not be administered during early single field study pregnancy because abortion could occur Few data on horses aPZP-22 and SpayVac® are formulated for longer efficacy and require further documentation of continued efficacy and of rate of unexpected effects. SOURCE: Asa et al. (1980b), Kirkpatrick et al. (1990), Thompson (2000), Kirkpatrick and Turner (2002, 2003, 2008), Stout and Colenbrander (2004), Imboden et al. (2006), Turner et al. (2007), Killian et al. (2008a), Gray (2009), Nuñez et al. (2009, 2010), Gray et al. (2010, 2011), Powers et al. (2011), Ransom (2012). might be more appropriate in populations in which a relatively large percentage of males could be treated. The strategy of treating only dominant stallions should be avoided. Late-season births could occur in mares treated with one of the vaccine products if reversal ­ occurred during the breeding season, but because most free-ranging mares give birth every other year rather than yearly, conceptions and births should become re-­ stablished in spring e or early summer. For mares that are able to maintain a pregnancy and give birth annually, reversal late in the season could have long-term consequences for all her future foals in that the 11-month gestation and the one or two ovulatory cycles needed to conceive can result in an about 12-month repeating cycle (see Garrott and Siniff, 1992).

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 133 TABLE 4-2  Behavioral Effects of Fertility-Control Methods Behavior PZPa,b GonaCon™ for Females Vasectomy Male sexual Increase or no change No change reported Longer breeding season reported Female sexual Increase or no change Decrease or no change Longer breeding season reported reported Social structure Possible decrease in band No change reported No change reported stability Activity budget Females may graze less No change reported No change reported Aggression Males may defend females No change reported Males defend females longer longer Spatial relationships Females may spend more No change reported No change reported time near male aIncludes results of studies of both liquid and pelleted (PZP-22) formulations; not all studies reported results in all the behavioral categories, and not all studies detected changes. bThere are no published reports on behavioral effects of SpayVac®. SOURCE: Rubenstein (1994), Turner et al. (1996), Asa (1999), Powell (1999, 2000), Thompson (2000), Stout and Colenbrander (2004), Imboden et al. (2006), Killian et al. (2008b), Gray (2009), Nuñez et al. (2009), Gray et al. (2010, 2011), Madosky et al. (2010, in review), Ransom et al. (2010), Powers et al. (2011). Given that chemical vasectomy appears to be an effective means of reducing male repro- duction with side effects that are likely to be minimal and not socially different from control- ling female fertility, strategies that simultaneously control male and female fertility are likely to be most biologically and economically cost-effective. Because of the polygynous nature of ­ horse and burro societies, the effect of chemically vasectomizing any one dominant harem- holding or territorial stallion will have a greater effect than contracepting any one fertile female. Moreover, because eventual male turnover is ensured, any long-term problems asso- ciated with chemical reproductive interventions are likely to be more reliably self-correcting in males than in females. When that safety factor is added to the problem of procuring large supplies of PZP vaccine in the short term, strategies of dual control allow large-scale and ­aggressive interventions that modeling (see Chapter 6) suggests will be necessary for regulat- ing population growth in humane and ecologically sound ways. Most of the PZP-vaccine research in horses (as reviewed in this chapter) has used the older, shorter-acting formulation that requires two initial injections and annual boosters. That formulation was the one licensed for use in horses at the time of the committee’s study. The longer-acting formulations (PZP-22 and SpayVac) were not licensed in the United States, so they were restricted to use for research purposes and not available for widespread ap- plication for management purposes. Similarly, GonaCon was registered with EPA for use in free-ranging horses in January 2013. Many state veterinary licensing agencies require that a vasectomy be performed by a licensed veterinarian, although the surgery is straightforward, but the simpler chemical vasectomy has not been systematically evaluated in horses, so test- ing in captive horses would be needed before widespread application in the field. CONCLUSIONS On the basis of the peer-reviewed literature and direct communication with scientists who are studying fertility control in horses and burros, the committee considers the three

OCR for page 93
134 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM most promising methods of fertility control to be PZP vaccines (in the forms of PZP-22 and SpayVac), GonaCon, and chemical vasectomy. Chemical vasectomy requires capture and handling, which could be straightforward in areas where BLM regularly gathers horses. It is more problematic in areas where it could be difficult or impossible to capture a sufficient number of animals for treatment to achieve a population effect. In addition, the efficacy of the two vaccines is higher if they are hand-injected rather than delivered by dart. Even in the case of liquid formulations of the vaccines that can in principle be delivered by dart, adequate delivery cannot be ensured. In addition, darting typically entails following animals by helicopter, which could be as stressful as gathering. Alternative methods for gaining closer access to animals for delivering injections should be sought for areas where gathering is not practical or possible. The vaccines can be effective for multiple years, but chemical vasectomy should be considered permanent. In cases in which reversibility is important and repeated treatment is practical, one of the vaccines would be preferable, with the caution that treatment for more than a few years may prolong recovery of fertility. A single treatment that induces lifetime infertility could be preferable in other situations. Even if a large fraction of a population’s males are chemically vasectomized and the sterility is permanent, the effects of such an extensive intervention on the dynamics of the population will be self-correcting. If gathers are an average of 5 years apart, younger males rising through the ranks as bachelors or adopting alternative routes to adulthood (Rubenstein and Nuñez, 2009) will be adding new genes to the pool at an increasing rate. Given that virtually all burro and some horse populations exhibit low levels of genetic heterozygosity, virtual elimination of local male fertility for short periods to allow trans- locations of males that have desired genetic characteristics into the population may be warranted. Such large-scale local chemical vasectomies would allow managers to enhance genetic diversity and reduce inbreeding of populations at risk. Moreover, it would be a self-correcting process as younger males that have the original genetic constitution mature and compete for reproductive opportunities with translocated males. Managing genetic diversity through translocation is discussed more thoroughly in the next chapter. All three methods should preserve the basic social unit and expression of sexual be- havior, although there have been conflicting reports on various effects of the vaccines on social interactions and on the cyclicity of estrous behavior. The major effect of the methods is that the typical breeding season would be extended for females that do not conceive (the implications are discussed at length above). No method has yet been developed that does not have some effect on physiology or behavior. However, the effects of not intervening to control or manage population numbers are potentially harsher than contraception; in the absence of natural predators, population numbers are likely to be limited by starva- tion (see Chapter 3 for discussion of the effect of density-dependent factors). Even if there were a method that had no effect other than preventing the production of young, the absence of young would alter the age structure of the population and could thereby af- fect harem dynamics. The most appropriate comparison that should be made in assessing the effects of any method of fertility control is with the current approach, gathering and removal. That is, to what extent does the prospective method affect health, herd structure, and the expression of natural behaviors relative to the effects of gathering? Three meth- ods (PZP-22 and SpayVac, GonaCon, and chemical vasectomy) are considered the most promising for managing fertility in free-ranging horses and burros because they have the fewest and least serious effects on those parameters. In addition, although their applica- tion requires handling the animals—­ athering—that process is no more disruptive than g the current method for controlling numbers, and it lacks the further disruption of removal

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 135 and relocation to long-term holding facilities. Considering all the current options, the three methods, either alone or in combination, offer the most acceptable alternative for manag- ing population numbers. However, further research is needed before they are ready for widespread deployment for horse population management. The current major gaps in knowledge about PZP-22, SpayVac, and GonaCon include a thorough understanding for each vaccine of percentage and duration of efficacy and the extent of its reversibility. GonaCon should be examined to evaluate the extent to which treated females continue to exhibit sexual behavior, which is important for maintaining natural social interactions. A study is needed to assess the efficacy and safety of potential agents for chemical vasectomy before it is used in free-ranging stallions during gathers. In light of the extensive research that has been conducted with liquid PZP, the likeli- hood that PZP-22 or SpayVac will produce new or unexpected effects, other than an ex- tended duration of action, is small, and this should reduce the scope of research that would be needed. Furthermore, given the decades of research on the earlier liquid formulation of PZP and its successful application in numerous free-ranging horse herds, liquid PZP can be used in many herd areas now. It might be applied not only in herds that are amenable to darting but during gathers for horses that are turned back onto the range. Even without a booster in the months just after a gather, any later inoculation will serve as a booster and initiate a period of infertility (J.W. Turner, University of Toledo, personal communication, August 2012). Thus, liquid PZP could serve as an interim fertility-control method until one of the other longer-acting methods is available. REFERENCES ACC&D (Alliance for Contraception in Cats & Dogs). 2012. Esterisol™ (“Zinc Neutering”). Product Profile and Position Paper. Available online at http://www.acc-d.org/ACCD%20docs/PPPP-Esterilsol.pdf/. Accessed November 14, 2012. Adams, T.E. and B.M. Adams. 1990. Reproductive function and feedlot performance of beef heifers actively i ­ mmunized against GnRH. Journal of Animal Science 68:2793-2802. Asa, C.S. 1986. Sexual behavior of mares. Veterinary Clinics of North America: Equine Practice 2:519-534. Asa, C.S. 1999. Male reproductive success in free-ranging feral horses. Behavioral Ecology and Sociobiology 47:89-93. Asa, C.S. 2005. Assessing efficacy and reversibility. Pp. 53-65 in Wildlife Contraception: Issues, Methods and Appli­ ation, C.S. Asa and I.J. Porton, eds. Baltimore, MD: Johns Hopkins University Press. c Asa, C.S. 2010. Reproductive physiology. Pp. 411-428 in Wild Mammals in Captivity: Principles and Techniques for Zoo Management, 2nd edition. D.G. Kleiman, K.V. Thompson, and C.K. Baer, eds. Chicago: University of Chicago Press. Asa, C.S., D.A. Goldfoot, M.C. Garcia, and O.J. Ginther. 1980a. Dexamethasone suppression of sexual behavior in ovariectomized mares. Hormones and Behavior 14:55-64. Asa, C.S., D.A. Goldfoot, M.C. Garcia, and O.J. Ginther. 1980b. Sexual behavior in ovariectomized and seasonally anovulatory mares. Hormones and Behavior 14:46-54. Asa, C.S., D.A. Goldfoot, M.C. Garcia, and O.J. Ginther. 1984. The effect of estradiol and progesterone on the sexual behavior of ovariectomized mares. Physiology & Behavior 33:681-686. Asa, C.S., I. Porton, A.M. Baker, and E.D. Plotka. 1996. Contraception as a management tool for controlling surplus animals. Pp. 451-467 in Wild Mammals in Captivity: Principles and Techniques, D.G. Kleiman, M.E. Allen, K.V. Thompson, and S. Lumpkin, eds. Chicago: University of Chicago Press. Asa, C.S. and I.J. Porton. 2010. Contraception as a management tool for controlling surplus animals. Pp. 469-482 in Wild Mammals in Captivity: Principles and Techniques for Zoo Management, 2nd edition. D.G. Kleiman, K.V. Thompson, and C.K. Baer, eds. Chicago: University of Chicago Press. Barber, M.R. and R.A. Fayrer-Hosken. 2000. Evaluation of somatic and reproductive immunotoxic effects of the porcine zona pellucida vaccination. Journal of Experimental Zoology Part A: Comparative and Experimental Biology 286:641-646. Bartell, J.A. 2011. Porcine Zona Pellucida Immuncontraception Vaccine for Horses. M.S. thesis. Oregon State University.

OCR for page 93
136 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Bartholow, J.M. 2004. Economic Analysis of Alternative Fertility Control and Associated Management Techniques for Three BLM Wild Horse Herds. Reston, VA: U.S. Geological Survey. Becker, C.D. and J.R. Ginsberg. 1990. Mother-infant behaviour of wild Grevy’s zebra: Adaptations for survival in semi-desert East Africa. Animal Behaviour 40:1111-1118. Berger, J. 1977. Organizational systems and dominance in feral horses in the Grand Canyon. Behavioral Ecology and Sociobiology 2:131-146. Berger, J. 1986. Wild Horses of the Great Basin: Social Competition and Population Size. Chicago: University of Chicago Press. BLM (Bureau of Land Management). 2003, revised 2005. Strategic Research Plan: Wild Horse and Burro Manage- ment. Fort Collins, CO: U.S. Department of the Interior. Blodgett, G.P. 2011. Normal field castration. Pp. 1557-1561 in Equine Reproduction, A.O. McKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Oxford: Wiley-Blackwell. Botha, A.E., M.L. Schulman, H.J. Bertschinger, A.J. Guthrie, C.H. Annandale, and S.B. Hughes. 2008. The use of a GnRH vaccine to suppress mare ovarian activity in a large group of mares under field conditions. Wildlife Research 35:548-554. Boyle, M.S., J. Skidmore, J. Zhang, and J.E. Cox. 1991. The effects of continuous treatment of stallions with high levels of a potent GnRH analogue. Journal of Reproduction and Fertility Supplement 44:169-182. Brinsko, S.P., E.L. Squires, B.W. Pickett, and T.M. Nett. 1998. Gonadal and pituitary responsiveness of stallions is not down-regulated by prolonged pulsatile administration of GnRH. Journal of Androlology 19:100-109. Brown, R.G., W.D. Bowen, J.D. Eddington, W.C. Kimmins, M. Mezei, J.L. Parson, and B. Pohajdak. 1997. Temporal trends in antibody production in captive grey, harp and hooded seals to a single administration immuno­ contraceptive vaccine. Journal of Reproductive Immunology 35:53-64. Cameron, E.Z., T.H. Setsaas, and W.L. Linklater. 2009. Social bonds between unrelated females increase reproduc- tive success in feral horses. Proceedings of the National Academy of Sciences of the United States of America 106:13850-13853. Carnevale, E.M. and O.J. Ginther. 1992. Relationships of age to uterine function and reproductive efficiency in mares. Theriogenology 37:1101-1115. Caswell, H. 2001. Matrix Population Models, 2nd edition. Sunderland, MA: Sinauer Associates. Chandra, R.K. 1996. Nutrition, immunity and infection: From basic knowledge of dietary manipulation of im- mune responses to practical application of ameliorating suffering and improving survival. Proceedings of the National Academy of Sciences of the United States of America 93:14304-14307. Chandra, R.K. and S.A.D. Amorin. 1992. Lipids and immunoregulation. Nutritional Research 12:S137-S145. Chapel, H.M. and P.J. August. 1976. Report of nine cases of accidental injury to man with Freund’s complete adjuvant. Clinical and Experimental Immunology 24:538-541. Chi, I. 1993. What we have learned from recent IUD studies: A researcher’s perspective. Contraception 48:81-108. Cooper, D.W. and E. Larsen. 2006. Immunocontraception of mammalian wildlife: Ecological and immunogenetic issues. Reproduction 132:821-828. Curtis, P.D., R.L. Pooler, M.E. Richmond, L.A. Miller, G.F. Mattfeld, and F.W. Quimby. 2002. Comparative effects of GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines for controlling reproduction in white-tailed deer (Odocoileus virginianus). Reproduction Supplement 60:131-141. Daels, P.F. and J.P. Hughes. 1995. Fertility control using intrauterine devices: An alternative for population control in wild horses. Theriogenology 44:629-639. Demas, G.E., D.L. Drazen, and R.J. Nelson. 2003. Reductions in total body fat decrease humoral immunity. Pro- ceedings of the Royal Society of London Series B 270:905-911. Eagle, T.C., E.D. Plotka, D.B. Siniff, and J.R. Tester. 1992. Efficacy of chemical contraception in feral mares. Wildlife Society Bulletin 20:211-216. Eagle, T.C., C.S. Asa, R.A. Garrott, and D.B. Siniff. 1993. Efficacy of dominant male contraception to reduce repro- duction in feral horses. Wildlife Society Bulletin 21:116-121. Eisemann, J.D., K.A. Fagerstone, and J.R. O’Hare. 2006. Wildlife contraceptives: A regulatory hot potato. Pp. 63-66 in Proceedings of the 22nd Vertebrate Pest Conference, R.M. Tim and J.M. O’Brien, eds. Davis: University of California. Elhay, M., A. Newbold, A. Britton, P. Turley, K. Dowsett, and J. Walker. 2007. Suppression of behavioural and physiological oestrus in the mare by vaccination against GnRH. Australian Veterinary Journal 85:39-45. Esho, J.O. and A.S. Cass. 1978. Recanalization rate following methods of vasectomy using interposition of fascial sheath of vas deferens. Journal of Urology 120:178-179. Fagerstone, K.A., R.M. Bullard, and C.A. Ramcy. 1990. Politics and economics of maintaining pesticide registra- tions. Vertebrate Pest Conference 14:8-11.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 137 Falconer, D.S. 1965. The inheritance of liability to certain diseases, estimated from the incidence among relatives. Annals of Human Genetics 29:51-76. Feist, J.D. and D.R. McCullough. 1975. Reproduction in feral horses. Journal of Reproduction and Fertility Supple- ment 23:13-18. Fielding, D. 1988. Reproductive characteristics of the jenny donkey—Equus asinus: A review. Tropical Animal Health and Production 20:161-166. Fitzgerald, B.P., K.D. Peterson, and P.J. Silvia. 1993. Effect of constant administration of a gonadotropin-releasing hormone agonist on reproductive activity in mares: Preliminary evidence on suppression of ovulation during the breeding season. American Journal of Veterinary Research 54:1746-1751. Fraker, M.A. 2012. SpayVac® for Wild Horses: A Lost-Lasting, Single-Dose pZP Contraceptive Vaccine. Webinar Presentation to the Bureau of Land Management and Members of the National Academy of Sciences’ Com- mittee to Review the Bureau of Land Management Wild Horse and Burro Management Program, May 3. Fraker, M.A., R.G. Brown, G.E. Gaunt, J.A. Kerr, and B. Pohajdak. 2002. Long-lasting single-dose immunocontra- ception of feral fallow deer in British Columbia. Journal of Wildlife Management 66:1141-1147. Fraker, M.A. and R.B. Brown. 2011. Efficacy of SpayVac® is excellent: A comment on Gray et al. (2010). Wildlife Research 38:537-538. Frenette, M.D., M.P. Dooley, and M.H. Pineda. 1986. Effect of flushing the vasa deferentia at the time of vasectomy on the rate of clearance of spermatozoa from the ejaculates of dogs and cats. American Journal of Veterinary Research 47:463-470. Garrott, R.A. and D.B. Siniff. ������������������������������������������������������������������������������������ 1992. Limitations of male-oriented contraception for controlling feral horse popula- tions. Journal of Wildlife Management 56:456-464. Gass, G.H., D. Coats, and N. Graham. 1964. Carcinogenic dose-response curve to oral diethylstilbestrol. Journal of the National Cancer Institute 33:971-977. Ginsberg, J.R. 1989. The ecology of female behaviour and male mating success in the Grevy’s zebra. Symposium of the Zoological Society of London 61:89-110. Ginther, O.J. 1979. Reproductive Biology of the Mare: Basic and Applied Aspects. Cross Plains, WI: EquiServices. Ginther, O.J., S.T. Scraba, and D.R. Bergfelt. 1987. Reproductive seasonality of the jenny. Theriogenology 27:587-592. Gionfriddo, J.P., J.D. Eisemann, K.J. Sullivan, R.S. Healey, and L.A. Miller. 2006. Field test of GonaCon™ im- munocontraceptive vaccine in free-ranging female white-tailed deer. Pp. 78-81 in Proceedings of the 22nd Vertebrate Pest Conference, R.M. Timm and J.M. O’Brien, eds. Davis: University of California. Gionfriddo, J.P., J.D. Eisemann, K.J. Sullivan, R.S. Healey, L.A. Miller, K.A. Fagerstone, R.M. Engeman, and C.A. Yoder. 2009. Field test of a single-injection gonadotrophin-releasing hormone immunocontraceptive vaccine in female white-tailed deer. Wildlife Research 36:177-184. Gionfriddo, J.P., A.J. DeNicola, L.A. Miller, and K.A. Fagerstone. 2011a. Efficacy of GnRH immunocontraception of wild white-tailed deer in New Jersey. Wildlife Society Bulletin 35:142-148. Gionfriddo, J.P., A.J. DeNicola, L.A. Miller, and K.A. Fagerstone. 2011b. Health effects of GnRH immuno­ contraception of wild white-tailed deer in New Jersey. Wildlife Society Bulletin 35:149-160. Goodloe, R.B. 1991. Immunocontraception, Genetic Management, and Demography of Feral Horses on Four Eastern U.S. Barrier Islands. Ph.D. dissertation. University of Georgia. Gotelli, N. 2001. A Primer of Ecology, 3rd edition. Sunderland, MA: Sinauer Associates. Gray, M.E. 2009. The Influence of Reproduction and Fertility Manipulation on the Social Behavior of Feral Horses (Equus caballus). Ph.D. dissertation. University of Nevada, Reno. Gray, M.E., D.S. Thain, E.Z. Cameron, and L.A. Miller. 2010. Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations. Wildlife Research 37:475-481. Gray, M.E., D.S. Thain, E.Z. Cameron, and L.A. Miller. 2011. Corrigendum to: Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations. Wildlife Research 38:260. Guillaume, D., G. Duchamp, J. Salazar-Ortiz, and P. Nagy. 2002. Nutrition influences the winter ovarian inactivity in mares. Theriogenology 58:593-597. Hageleit, M., A. Daxenberger, W.D. Kraetzl, A. Kettler, and H.H.D. Meyer. 2000. Dose-dependent effects of m ­ elengestrol acetate (MGA) on plasma levels of estradiol, progesterone and luteinizing hormone in cycling heifers and influence on oestrogen residues in edible tissues. Acta Pathologica Microbiologica and Immuno- logica Scandinavica 108:847-854. Henry, M., S.M. McDonnell, L.D. Lodi, and E.L. Gastal. 1991. Pasture mating behaviour of donkeys (Equus asinus) at natural and induced oestrus. Journal of Reproduction and Fertility Supplement 44:77-86. Hobbs, N.T., D.C. Bowden, and D.L. Baker. 2000. Effects of fertility control on populations of ungulates: General, stage-structured models. Journal of Wildlife Management 64:473-491. Holtan, D.W., E.L. Squires, D.R. Lapin, and O.J. Ginther. 1979. Effect of ovariectomy on pregnancy in mares. J ­ ournal of Reproduction and Fertility Supplement 27:457-463.

OCR for page 93
138 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Homsy, J., W.J.W. Morrow, and J.A. Levy. 1986. Nutrition and autoimmunity: A review. Clinical Experimental Immunology 65:473-488. Hooper, R.N., T.S. Taylor, D.D. Varner, and T.L. Blanchard. 1993. Effects of bilateral ovariectomy via colpotomy in mares: 23 cases (1984-1990). Journal of the American Veterinary Medical Association 203:1043-1046. Houston, A.I., J.M. McNamara, Z. Barta, and K.C. Klasing. 2007. The effect of energy reserves and food availability on optimal immune defence. Proceedings of the Royal Society of London Series B 274:2835-2842. Imboden, I., F. Janett, D. Burger, M.A. Crowe, M. Hassig, and R. Thun. 2006. Influence of immunization against GnRH on reproductive cyclicity and estrous behavior in the mare. Theriogenology 66:1866-1875. Janett, F., R. Stump, D. Burger, and R. Thun. 2009. Suppression of testicular function and sexual behavior by vac- cination against GnRH (Equity™) in the adult stallion. Animal Reproduction Science 115:88-102. Jensen, H. 2000. Social Structure and Activity Patterns among Selected Pryor Mountain Wild Horses. Report to the Billings Field Office, Bureau of Land Management. Johnson, C., S. McMeen, and D. Thompson. 2002. Effects of multiple GnRH analogue (deslorelin acetate) implants on cyclic mares. Theriogenology 58:469-471. Junaidi, A., P.E. Williamson, J.M. Cummins, G.B. Martin, M.A. Blackberry, and T.E. Trigg. 2003. Use of a new drug delivery formulation of the gonadotrophin-releasing hormone analogue Deslorelin for reversible long-term contraception in male dogs. Reproduction, Fertility and Development 15:317-322. Junaidi, A., P.E. Williamson, G.B. Martin, M.A. Blackberry, J.M. Cummins, and T.E. Trigg. 2009. Dose-response studies for pituitary and testicular function in male dogs treated with the GnRH superagonist, deslorelin. Reproduction in Domestic Animals 44:725-734. Killian, G., L.A. Miller, N.L. Diehl, J. Rhyan, and D. Thain. 2004. Evaluation of three contraceptive approaches for population control of wild horses. Pp. 263-268 in Proceedings of the 21st Vertebrate Pest Conference, R.M. Timm and W.P. Gorenzel, eds. Davis: University of California. Killian, G., D. Wagner, and L. Miller. 2005. Observations on the use of the GnRH vaccine Gonacon™ in male white-tailed deer (Odocoileus virginianus). Pp. 256-263 in Proceedings of the 11th Wildlife Damage Manage- ment Conference, D.L. Nolte and K.A. Fagerstone, eds. Fort Collins, CO: National Wildlife Research Center. Killian, G., L. Miller, J. Rhyan, and H. Doten. 2006. Immunocontraception of Florida feral swine with a single-dose GnRH vaccine. American Journal of Reproductive Immunology 55:378-384. Killian, G., D. Thain, N.K. Diehl, J. Rhyan, and L. Miller. 2008a. Four-year contraception rates of mares treated with single-injection porcine zona pellucida and GnRH vaccines and intrauterine devices. Wildlife Research 35:531-539. Killian, G., D. Wagner, K. Fagerstone, and L. Miller. 2008b. Long-term efficacy and reproductive behavior associ- ated with Gonacon™ use in white-tailed deer (Odocoileus virginianus). Pp. 240-243 in Proceedings of the 23rd Vertebrate Pest Conference, R.M. Timm and M.B. Madon, eds. Davis: University of California. Killian, G., T.J. Kreeger, J. Rhyan, K. Fagerstone, and L. Miller. 2009. Observations on the use of Gonacon™ in captive female elk (Cervus elaphus). Journal of Wildlife Diseases 45:184-188. Kirkpatrick, J.F. and A. Turner. 2002. Reversibility of action and safety during pregnancy of immunization against porcine zona pellucida in wild mares (Equus caballus). Reproduction Supplement 60:197-202. Kirkpatrick, J.F. and A. Turner. 2003. Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses. Journal of Applied Animal Welfare Science 6:301-308. Kirkpatrick, J.F. and A. Turner. 2007. Immunocontraception and increased longevity in equids. Zoo Biology 26:237-244. Kirkpatrick, J.F. and A. Turner. 2008. Achieving population goals in a long-lived wildlife species (Equus caballus) with contraception. Wildlife Research 35:513-519. Kirkpatrick, J.F., I.K.M. Liu, and J.W. Turner, Jr. 1990. Remotely-delivered immunocontraception in feral horses. Wildlife Society Bulletin 18:326-330. Kirkpatrick, J.F., I.M. Liu, J.W. Turner, Jr., and M. Bernoco. 1991. Antigen recognition in feral mares previously immunized with porcine zona pellucida. Journal of Reproduction and Fertility Supplement 44:321-325. Kirkpatrick, J.F., I.M.K. Liu, J.W. Turner, Jr., R. Naugle, and R. Keiper. 1992. Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function in feral horses (Equus caballus). Journal of Reproduc- tion and Fertility 94:437-444. Kirkpatrick, J.F., R. Naugle, I.K.M. Liu, M. Bernoco, and J.W. Turner, Jr. 1995. Effects of seven consecutive years of porcine zona pellucida contraception on ovarian function in feral mares. Biology of Reproduction Mono- graphs 1:411-418. Kirkpatrick, J.F., R.O. Lyda, and K.M. Frank. 2011. Contraceptive vaccines for wildlife: A review. American Journal of Reproductive Immunology 66:40-50. Klingel, H. 1975. Social organization and reproduction in equids. Journal of Reproduction and Fertility Supple- ment 23:7-11.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 139 Lauderdale, J.W., L.S. Goyings, L.F. Krzeminski, and R.G. Zimbelman. 1977. Studies of a progestogen (MGA) as related to residues and human consumption. Journal of Toxicology and Environmental Health 3:5-33. Liehr, J.G. 2001. Genotoxicity of the steroidal oestrogens oestrone and oestradiol: Possible mechanism of uterine and mammary cancer development. Human Reproduction Update 7:273-281. Linklater, W.L., E.Z. Cameron, E.O. Minot, and K.J. Stafford. 1999. Stallion harassment and the mating system of horses. Animal Behavior 58:295-306. Liu, I.K.M., M. Bernoco, and M. Feldman. 1989. Contraception in mares heteroimmunized with pig zona ­pellucidae. Journal of Reproduction and Fertility 85:19-28. Liu, I.K.M., J.W. Turner, Jr., E.M.G. Van Leeuwen, D.R. Flanagan, J.L. Hedrick, K. Murata, V.M. Lane, and M.P. Morales-Levy. 2005. Persistence of anti-zonae pellucidae antibodies following a single inoculation of porcine zonae pellucidae in the domestic equine. Reproduction 129:181-190. Locke, S.L., M.W. Cook, L.A. Harveson, D.S. Davis, R.R. Lopez, N.J. Silvy, and M.A. Fraker. 2007. Effectiveness of Spayvac® for reducing white-tailed deer fertility. Journal of Wildlife Diseases 43:726-730. Ludwig, C., P.O. Desmoulins, M.A. Driancourt, S. Goericke-Pesch, and B. Hoffmann. 2009. Reversible down­ regulation of endocrine and germinative testicular function (hormonal castration) in the dog with the GnRH- agonist azagly-nafarelin as a removable implant “Gonazon”; a preclinical trial. Theriogenology 71:1037-1045. Lyda, R.O., J.R. Hall, and J.F. Kirkpatrick. 2005. A comparison of Freund’s Complete and Freund’s Modified Adjuvants used with a contraceptive vaccine in wild horses (Equus caballus). Journal of Zoo and Wildlife Medicine 36:610-616. Madosky, J., D. Rubenstein, J. Howard, and S. Stuska. 2010. The effect of immunocontraception on harem fidelity in a feral horse (Equus caballus) population. Applied Animal Behaviour Science 128:50-56. Madosky, J., J. Howard, D. Rubenstein, and S. Stuska. In review. Synchrony of time budgets, social interactions, and harem stability in a feral horse population. Malmgren, L., O. Andresen, and A.M. Dalin. 2001. Effect of GnRH immunisation on hormonal levels, sexual behaviour, semen quality and testicular morphology in mature stallions. Equine Veterinary Journal 33:75-83. Massei, G., D.P. Cowan, J. Coats, F. Gladwell, J.E. Lane, and L.A. Miller. 2008. Effect of the GnRH vaccine GonaCon on the fertility, physiology and behaviour of wild boar. Wildlife Research 35:540-547. May, R.M. and D.I. Rubenstein. 1985. Reproductive strategies. Pp. 1-23 in Reproduction in Mammals, C.R. Austin and R.V. Short, eds. Cambridge, UK: Cambridge University Press. McCue, P.M. and R.A. Ferris. 2011. The abnormal estrous cycle. Pp. 1754-1768 in Equine Reproduction, 2nd edition. A.O. McKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Hoboken, NJ: Wiley-Blackwell. McCue, P.M. and A.O. McKinnon. 2011. Ovarian abnormalities. Pp. 2123-2136 in Equine Reproduction, 2nd edi- tion. A.O. McKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Hoboken, NJ: Wiley-Blackwell. Miller, L.A., B.E. Johns, and G.J. Killian. 2000. Immunocontraception of white-tailed deer with GnRH vaccine. American Journal of Reproductive Immunology 44:266-274. Miller, L.A., J.C. Rhyan, and M. Drew. 2004. Contraception of bison by GnRH vaccine: A possible means of decreas- ing transmission of brucellosis in bison. Journal of Wildlife Diseases 40:725-730. Miller, L.A., J.P. Gionfriddo, J.C. Rhyan, K.A. Fagerstone, D.C. Wagner, and G.J. Killian. 2008. GnRH immuno­ contraception of male and female white-tailed deer fawns. Human-Wildlife Conflicts 2:93-101. Miller, L.A., K.A. Fagerstone, D.C. Wagner, and G.J. Killian. 2009. Factors contributing to the success of a single- shot, multiyear PZP immunocontraceptive vaccine for white-tailed deer. Human-Wildlife Conflicts 3:103-115. Mitchell, D. and W.R. Allen. 1975. Observations on reproductive performance in the yearling mare. Journal of Reproduction and Fertility Supplement 23:531-536. Montovan, S.M., P.F. Daels, J. Rivier, J.P. Hughes, G.H. Stabenfeldt, and B.L. Lasley. 1990. The effect of a potent GnRH agonist on gonadal and sexual activity in the horse. Theriogenology 33:1305-1321. Moss, W.M. 1992. A comparison of open-ended versus closed-end vasectomies: A report on 6220 cases. Contracep- tion 46:521-525. Munson, L., J.E. Bauman, C.S. Asa, W. Jochle, and T.E. Trigg. 2001. Efficacy of the GnRH analogue deslorelin for suppression of oestrus cycle in cats. Journal of Reproduction and Fertility Supplement 57:269-273. Murthy, V., A.R. Norman, Y. Barbachano, C.C. Parker, and D.P. Dearnaley. 2007. Long-term effects of a short course of neoadjuvant luteinizing hormone-releasing hormone analogue and radical radiotherapy on the hormonal profile in patients with localized prostate cancer. British Journal of Urology International 99:1380-1382. Naden, J., E.L. Squires, and T.M. Nett. 1990. Effect of maternal treatment with altrenogest on age at puberty, hor- mone concentrations, pituitary response to exogenous GnRH, oestrous cycle characteristics and fertility of fillies. Journal of Reproduction and Fertility 88:185-195. Nejat, R.J., H.H. Rashid, E. Bagiella, A.E. Katz, and M.C. Benson. 2000. A prospective analysis of time to nor- malization of serum testosterone after withdrawal of androgen deprivation therapy. Journal of Urology 164:1891-1894.

OCR for page 93
140 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Nelson, K.J. 1978. On the Question of Male-Limited Population Growth in Feral Horses (Equus caballus). M.S. thesis. New Mexico State University, Las Cruces. Neuhauser, S., F. Palm, F. Ambuehl, and C. Aurich. 2008. Effects of altrenogest treatment of mares in late preg- nancy on parturition and on neonatal viability of their foals. Experimental and Clinical Endocrinology and Diabetes 116:423-428. Nipken, C. and K.H. Wrobel. 1997. A quantitative morphological study of age-related changes in the donkey testis in the period between puberty and senium. Andrologia 29:149-161. Nishikawa, Y. 1959. Studies on reproduction in horses. Tokyo: Japan Racing Association. Nobelius, A.M. 1992. Gestagens in the Mare: An Appraisal of the Effects of Gestagenic Steroids on Suppression of Oestrus in Mares. M.S. thesis. Monash University, Australia. NRC (National Research Council). 1980. Wild and Free-Roaming Horses and Burros: Current Knowledge and Recommended Research. Phase I Final Report. Washington, DC: National Academy Press. NRC (National Research Council). 1991. Wild Horse Populations: Field Studies in Genetics and Fertility. Washing- ton, DC: National Academy Press. Nuñez, C.M.V., J.S. Adelman, C. Mason, and D.I. Rubenstein. 2009. Immunocontraception decreased group ­fidelity in a feral horse population during the non-breeding season. Applied Animal Behavior Science 117:74-83. Nuñez, C.M.V., J.S. Adelman, and D.I. Rubenstein. 2010. Immunocontraception in wild horses (Equus caballus) extends reproductive cycling beyond the normal breeding season. PLoS One 5:e13635. O’Brien, P.A., R. Kulier, F.M. Helmerhorst, M. Usher-Patel, and C. d’Arcangues. 2008. Copper-containing, framed intrauterine devices for contraception: A systematic review of randomized controlled trials. Contraception 77:318-327. Oli, M.K. and F.S. Dobson. 2003. The relative importance of life-history variables to population growth rate in mammals: Cole’s prediction revisited. American Naturalist 161:422-440. Padmanabhan, W. and A. McNeilly. 2001. Is there an FSH-releasing factor? Reproduction 121:21-30. Pech, R., G.M. Hood, J. McIlroy, and G. Saunders. 1997. Can foxes be controlled by reducing their fertility? Repro- duction, Fertility and Development 9:41-50. Pelahach, L.M., H.E., Greaves, M.B. Porter, A. Desvousges, and D.C. Sharp. 2002. The role of estrogen and proges- terone in the induction and dissipation of uterine edema in mares. Theriogenology 58:441-444. Perry, K.R., W.M. Arjo, K.S. Bynum, and L.A. Miller. 2006. GnRH single-injection immunocontraception in black- tailed deer. Pp. 72-77 in Proceedings of the 22nd Vertebrate Pest Conference, R.M. Timm and J.M. O’Brien, eds. Davis: University of California. Pickett, B.W., L.C. Faulkner, and J.L. Voss. 1975. Effect of season on some characteristics of stallion semen. Journal of Reproduction and Fertility Supplement 23:25-28. Pineda, M.H. and M.P. Dooley. 1984. Surgical and chemical vasectomy in the cat. American Journal of Veterinary Research 45:291-300. Pineda, M.H., T.J. Reimers, L.C. Faulkner, M.C. Hopwood, and G.E. Seidel, Jr. 1977. Azoospermia in dogs induced by injection of sclerosing agents into the caudae of the epididymides. American Journal of Veterinary Re- search 38:831-838. Pinto, C.R.F. 2011. Progestagens and progesterone. Pp. 1811-1819 in Equine Reproduction, 2nd edition. A.O. M ­ cKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Oxford: Wiley-Blackwell. Plosker, G.L. and R.N. Brogden. 1994. Leuprorelin. A review of its pharmacology and therapeutic use in prostatic cancer, endometriosis and other sex hormone-related disorders. Drugs 48:930-967. Plotka, E.D. and U.S. Seal. 1989. Fertility control in female white-tailed deer. Journal of Wildlife Diseases 25:643-646. Plotka, E.D., T.C. Eagle, D.N. Vevea, A.L. Koller, D.B. Siniff, J.R. Tester, and U.S. Seal. 1988. Effects of hormone implants on estrus and ovulation in feral mares. Journal of Wildlife Diseases 24:507-514. Plotka, E.D., D.N. Vevea, T.C. Eagle, J.R. Tester, and D.B. Siniff. 1992. Hormonal contraception of feral mares with Silastic rods. Journal of Wildlife Diseases 28:255-262. Pollock, J.I. 1980. Behavioral ecology and body condition changes in New Forest ponies. Royal Society for the Prevention of Cruelty to Animals Scientific Publication 6. 113 pp. Porter, M. and D. Sharp. 2002. Gonadotropin-releasing hormone receptor trafficking may explain the relative resistance to pituitary desensitization in mares. Theriogenology 58:523-526. Porton, I.J. and K. DeMatteo. 2005. Contraception in non-human primates. Pp. 119-148 in Wildlife Contraception: Issues, Methods, and Applications, C.S. Asa and I.J. Porton, eds. Baltimore, MD: Johns Hopkins University Press. Powell, D.M. 1999. Preliminary evaluation of porcine zona pellucida (PZP) immunocontraception for behavioral effects. Journal of Applied Animal Welfare Science 2:321. Powell, D.M. 2000. Evaluation of Effects of Contraceptive Population Control on Behavior and the Role of Social Dominance in Female Feral Horses, Equus caballus. Ph.D. dissertation. University of Maryland, College Park.

OCR for page 93
METHODS AND EFFECTS OF FERTILITY MANAGEMENT 141 Powell, D.M. and S.L. Montfort. 2001. Assessment: Effects of porcine zona pellucida immunocontraception on estrous cyclicity in feral horses. Journal of Applied Animal Welfare Science 4:271-284. Powers, J.G., D.L. Baker, T.L. Davis, M.M. Conner, A.H. Lothridge, and T.M. Nett. 2011. Effects of gonadotropin- releasing hormone immunization on reproductive function and behavior in captive female Rocky Mountain elk (Cervus elaphus nelsoni). Biology of Reproduction 85:1152-1160. Pugh, D. 2002. Donkey reproduction. Pp. 113-114 in the 48th Annual Convention Proceedings of the American Association of Equine Practitioners. Lexington, KY: AAEP. Ransom, J.I. 2012. Population Ecology of Feral Horses in an Era of Fertility Control Management. Ph.D. disserta- tion. Colorado State University, Fort Collins. Ransom, J.I., B.S. Cade, and N.T. Hobbs. 2010. Influences of immunocontraception on time budgets, social behav- ior, and body condition in feral horses. Applied Animal Behavior Science 124:51-60. Ransom, J.I., J.E. Roelle, B.S. Cade, L. Coates-Markle, and A.J. Kane. 2011. Foaling rates in feral horses treated with the immunocontraceptive porcine zona pellucida. Wildlife Society Bulletin 35:343-352. Rivera, R. and K. Best. 2002. Current opinion: Consensus statement on intrauterine contraception. Contraception 65:385-388. Rodgerson, D.H. and D.A. Loesch. 2011. Ovariectomy. Pp. 2564-2573 in Equine Reproduction, 2nd edition. A.O. McKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Oxford: Wiley-Blackwell. Roelle, J.E. and J.I. Ransom. 2009. Injection-site reactions in wild horses (Equus caballus) receiving an immuno­ contraceptive vaccine. U.S. Geological Survey Scientific Investigations Report 2009-5038. Fort Collins, CO: U.S. Geological Survey. Roser, J.F. and J.P. Hughes. 1991. Prolonged pulsatile administration of gonadotropin-releasing hormone (GnRH) to fertile stallions. Journal of Reproduction and Fertility Supplement 44:155-168. Rubenstein, D.I. 1981. Behavioural ecology of island feral horses. Equine Veterinary Journal 13:27-34. Rubenstein, D.I. 1986. Ecology and sociality in horses and zebras. Pp. 282-302 in Ecological Aspects of Social Evolu- tion, D.I. Rubenstein and L.W. Wrangham, eds. Princeton, NJ: Princeton University Press. Rubenstein, D.I. 1994. The ecology of female social behaviour in horses, zebras and asses. Pp. 13-28 in Animal Societies, Individuals, Interactions, and Organization, P.J. Jarman and A. Rossiter, eds. Kyoto, Japan: Kyoto University Press. Rubenstein, D.I. and C.M. Nuñez. 2009. Sociality and reproductive skew in horses and zebras. Pp. 196-226 in Re- productive Skew in Vertebrates: Proximate and Ultimate Causes, R. Hager and C.B. Jones, eds. Cambridge, UK: Cambridge University Press. Rutberg, A.T. 1990. Intergroup transfer in Assateague pony mares. Animal Behaviour 40:945-952. Rutberg, A.T. and R.E. Naugle. 2008. Population-level effects of immunocontraception in white-tailed deer (Odocoileus virginianus). Wildlife Research 35:494-501. Samper, J.C. 1997. Ultrasonographic appearance and the pattern of uterine edema to time ovulation in mares. Pp. 189-191 in the 43rd Annual Convention Proceedings of the American Association of Equine Practitioners. Lexington, KY: AAEP. Santen, R. 1998. Biological basis of the carcinogenic effects of estrogen. Obstetrical and Gynecological Survey 53:10S-18S. Sharp, D.C. and O.J. Ginther. 1975. Stimulation of follicular activity and estrous behavior in anestrous mares with light and temperature. Journal of Animal Science 41:1368-1372. Sieme, H., M.H.T. Troedsson, S. Weinrich, and E. Klug. 2004. Influence of exogenous GnRH on sexual behavior and frozen/thawed semen viability in stallions during the non-breeding season. Theriogenology 61:159-171. Silber, S.J. 1989. Pregnancy after vasovasostomy for vasectomy reversal: A study of factors affecting long-term return of fertility in 282 patients followed for 10 years. Human Reproduction 4:318-322. Singer, F.J. and K.A. Schoenecker, compilers. 2000. Managers’ Summary—Ecological Studies of the Pryor Moun- tain Wild Horse Range, 1992-1997. Fort Collins, CO: U.S. Geological Survey. Sivin, I. 1993. Another look at the Dalkon Shield: Meta analysis underscores its problems. Contraception 48:1-12. Squires, E.L. 2011. Gonadotropin releasing hormones. Pp. 1820-1824 in Equine Reproduction, 2nd edition. A.O. McKinnon, E.L. Squires, W.E. Vaala, and D.D. Varner, eds. Oxford: Wiley-Blackwell. Stahl, J.T. and M.K. Oli. 2006. Relative importance of avian life-history variables to population growth rate. Eco- logical Modelling 198:183-194. Stahlbaum, C.C. and K.A. Houpt. 1989. The role of the flehmen response in the behavioral repertoire of the stallion. Physiology and Behavior 45:1207-1214. Stearns, S.C. 1992. The Evolution of Life Histories. Oxford: Oxford University Press. Stevens, E.F. 1990. Instability of harems of feral horses in relation to season and presence of subordinate stallions. Behaviour 112:149-161.

OCR for page 93
142 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Storer, W.A., D.L. Thompson, R.M. Gilley, and P.J. Burns. 2009. Evaluation of injectable sustained release progestin formulations for suppression of estrus and ovulation in mares. Journal of Equine Veterinary Science 29:33-36. Stout, T.A.E. and B. Colenbrander. 2004. Suppressing reproductive activity in horses using GnRH vaccines, a ­ ntagonists or agonists. Animal Reproduction Science 82-83:633-643. Stuska, S. 2012. Shackleford Banks Horse Herd Update. September 25. Beaufort, NC: Foundation for Shackleford Horses. Tankeyoon, M., N. Dusitsin, S. Chalapati, S. Koetsawang, S. Saibiang, M. Sas, J.J. Gellen, O. Ayeni, R. Gray, A. Pinol, and L. Zegers. 1984. Effects of hormonal contraceptives on milk volume and infant growth: WHO Special Programme of Research and Development and Research Training in Human Reproduction. Contraception 30:505-522. Thompson, D.L. 2000. Immunization against GnRH in male species (comparative aspects). Animal Reproduction Science 60:459-469. Tomasgard, G. and E. Benjaminsen. 1975. Plasma progesterone in mares showing estrus during pregnancy. Nordisk Veterinærmedicin 27:570-574. Toydemir, T.S.F., M.R. Kılıçarslan, and V. Olgaç. 2012. Effects of the GnRH analogue deslorelin implants on repro- duction in female domestic cats. Theriogenology 77:662-674. Turkstra, J., F. Van Der Meer, J. Knaap, P. Rottier, K. Teerds, B. Colenbrander, and R. Meloen. 2005. Effects of GnRH immunization in sexually mature pony stallions. Animal Reproduction Science 86:247-259. Turner, A. and J.F. Kirkpatrick. 2002. Effects of immunocontraception on population, longevity and body condition in wild mares (Equus caballus). Reproduction Supplement 60:187-195. Turner, J.W., Jr. and J.F. Kirkpatrick. 1982. Androgens, behavior and fertility control in feral stallions. Journal of Reproduction and Fertility Supplement 32:79-87. Turner, J.W., Jr., I.K.M. Liu, and J.F. Kirkpatrick. 1996. Remotely delivered immuno-contraception in free-roaming feral burros (Equus asinus). Journal of Reproduction and Fertility 107:31-35. Turner, J.W., Jr., I.K.M. Liu, A.T. Rutberg, and J.F. Kirkpatrick. 1997. Immunocontraception limits foal production in free-roaming feral horses in Nevada. Journal of Wildlife Management 61:873-880. Turner, J.W., Jr., I.K.M. Liu, D.R. Flanagan, A.T. Rutberg, and J.F. Kirkpatrick. 2001. Immunocontraception in feral horses: One inoculation provides one year of infertility. Journal of Wildlife Management 65:235-241. Turner, J.W., Jr., I.K.M. Liu, D.R. Flanagan, A.T. Rutberg, and J.F. Kirkpatrick. 2007. Immunocontraception in wild horses: One inoculation provides two years of infertility. Journal of Wildlife Management 71:662-667. Turner, J.W., A.T. Rutberg, R.E. Naugle, M.A. Kaur, D.R. Flanagan, H.J. Bertschinger, and I.K.M. Liu. 2008. Controlled-release components of PZP contraceptive vaccine extend duration of infertility. Wildlife Research 35:555-562. Vandeplassche, G.M., J.A. Wesson, and O.J. Ginther. 1981. Behavioral, follicular and gonadotropin changes during the estrous cycle in donkeys. Theriogenology 16:239-249. Vanderwall, D.K. 2008. Early embryonic loss in the mare. Journal of Equine Veterinary Science 28:691-702. Vanderwall, D.K., G.L. Woods, D.A. Freeman, J.A. Weber, R.W. Rock, and D.F. Tester. 1993. Ovarian follicles, ovula- tions, and progesterone concentrations in aged versus young mares. Theriogenology 40:21-32. Yurewicz, E.C., A.G. Sacco, and M.G. Subramanian. 1983. Isolation and preliminary characterization of a purified pig zona antigen (PPZA) from porcine oocytes. Biology of Reproduction 29:511-523. Zeng, W., S. Ghosh, Y.F. Lau, L.E. Brown, and D.C. Jackson. 2002. Highly immunogenic and totally synthetic lipopeptides as self-adjuvanting immunocontraceptive vaccines. Journal of Immunology 169:4905-4912.