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OCR for page 215
APPENDIX
CAnimal Genetic Resources: Sperm
fan Parsonson
The importance of using semen in the dissemination of the ge-
netic diversity of domesticated animal species is well recog-
nized. Increases in highly desirable genetic characteristics and
in the productivity of the various animal species have established
artificial breeding (AB) as an efficient and reliable method in animal
husbandry.
Technical progress in the cryopreservation of semen and in mod-
ern handling, storing, and transport systems have made international
trade in animal semen an important segment of the commerce of
many countries. These technical achievements have been a critical
factor in the improvement of livestock worldwide. The portability
and keeping qualities of cryopreserved semen have provided access
to gene pools around the world. As techniques are developed for the
collection, handling, and storage of semen from additional animal
species not widely used at present, further expansion of world ge-
netic resources will occur (Seidel, 1986~.
Authorities responsible for disease control within a country usu-
ally require specific health standards for the donors standing at AB
centers, as well as general standards for the operation of the centers
and for the handling, storage, and quality of the gametes produced
from the centers. International trade requires standards and tests for
Ian Parsonson was assistant chief of the Australian Animal Health Laboratory at the Com-
monwealth Scientific and Industrial Research Organization. He is a member of the Australian
Commonwealth Government Genetic Manipulation Advisory Committee.
215
OCR for page 216
216 / Appendix C
semen, which are set out in protocols by the importing countries.
These protocols and regulations define the standards for the donor
animals, the AB centers, and the bacteriological control of the prod-
uct. Generally, the quality control requirements set high standards
for most AB establishments. The standards include disease control
conditions for entry of animals into centers, for health standards for
animals once in the centers, and for sale of semen from donors at the
AB center.
Standards for the importation of semen from countries in Europe,
North America, and Australasia are comparable; they include tests
for disease agents known to be exotic to the importing country. The
advantage of cryopreserved semen is that it can be held pending verifi-
cation of the accredited health status of the donors before being released
for sale. An additional advantage of holding cryopreserved semen is
that progeny testing can be conducted to evaluate genetic gain or to
detect genetic defects before general release of the semen samples.
Transmission of disease agents in semen or in spermatozoa has
been seen as potentially the most likely method of spread of infec-
tious disease both domestically and internationally. The realization
that cryopreservation, antibiotics, and semen extenders such as milk
and egg yolk citrate also assisted in the preservation of many patho-
gens led to the development of health standards for donors and codes
of practice for AB centers. Adherence to protocols for the health
status of animals in AB centers and use of strict aseptic collection,
handling, and preservation methods can lead to a high-quality, mini-
mally infected product. Artificial breeding also provides a method of
disease control through the use of specific pathogen free semen.
Artificial breeding centers are the basis of national disease con-
trol programs in many countries and are usually a requirement for an
export trade in semen. The Office International des Epizooties (OIE)
has developed recommendations for certification of AB centers on
the basis of sanitary codes for control of disease and standards for
processing semen (Office International des Epizooties, 1986~. Three
disease-free categories regional freedom, herd freedom, and indi-
vidual donor and its gametes freedom from specific diseases-form
the basis for international trade in animal gametes and in particular
semen.
MAJOR SPECIES OF DOMESTIC LIVESTOCK INVOLVED IN
INTERNATIONAL GERMPLASM TRADE
The major species of domestic livestock involved in international
trade in germplasm are cattle, sheep, pigs, goats, horses, and poultry.
OCR for page 217
Appendix C / 217
Species involved at a much reduced level include buffalo, deer, dogs,
and various types of zoological animals. In addition, there is some
trade in insect germplasm (bees), in fish germplasm, and in certain
lines of laboratory animals, usually as frozen embryos. The major
species used in AB programs throughout, however, is cattle (Bos taurus
and Bos indicus), and it is through the production of semen from this
species that the advantages and problems of artificial breeding have
been identified.
When bovine semen was first used for artificial breeding, the
distribution of the semen was restricted to local regions because of
the limited viability of the product and the lack of mobility of the
. .
Inseminators.
^. ~
There was a relationship between the fertility of par-
ticular bulls and the pregnancy rate of cows inseminated with their
semen, and soon, bulls whose nonreturn rates were lower than ex-
pected standards were detected. It also soon became obvious that
certain venereal diseases were being transmitted with the semen. Some
of the diseases, such as brucellosis (Brucella abortus) and trichomoniasis
(Trichomonas foetus), had been identified as causes of reproductive
failure, and attempts were made to diagnose infected bulls. As bo-
vine semen became an article of commerce, quality control standards
became mandatory in many countries. Several other infectious agents
affecting fertility were added to the growing list of pathogens that
might be present in semen, including Campylobacteriosis (Campylobacter
fetus var. venerealis and C. intermedius).
The cryopreservation of extended semen added to the problem in
that correctly frozen semen also preserved the microorganisms that
were present as contaminants. Antibiotics were added to semen ex-
tenders not so much to eradicate the microorganisms present, but
rather to reduce their potential to cause harm. Along with these
steps, research into improved aseptic collection and handling of fresh
semen showed the importance of careful attention to temperature
and temperature gradients for cryopreservation.
ARTIFICIAL BREEDING CENTERS AND DONOR
ANIMAL REQUIREMENTS
The Australian Standing Committee on Agriculture has required
that AB centers comply with Australian standards to be eligible for
registration with the Australian Quarantine Inspection Service for the
export of semen. Bovine semen production centers are licensed un-
der state legislation to produce semen for sale from bulls kept within
the center and judged to be disease free according to minimum stan-
dards set out in the Minimum Health Standards for Stock Standing at
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218 / Appendix C
Licensed or Approved Artificial Breeding Centers in Australia (Australian
Quarantine and Inspection Service, 1988~.
A center is a quarantine area and is under veterinary supervision.
The center must have facilities within the fully health-tested area for
accommodation of stock and for collection of semen from the stock.
It must have a processing laboratory and storage facilities for semen
derived from the stock. Other requirements include providing for
treatment of sick animals, introducing new stock without endanger-
ing those already present, and maintaining the center as a strict quar-
antine area.
Prior to entering the center, cattle are examined for freedom from
infectious disease and, as possible, tested for hereditary defects (for
example, mannosidase tests for Angus cattle and crosses of Angus
extraction) to detect carriers. The health tests require freedom from
brucellosis (Brucella abortus), tuberculosis (Mycobacterium bovis), and
leptospirosis (L. Pomona and L. hardjo). Treatment with dihydrostrepto-
mycin is also required but only after tests have been made for free-
dom from campylobacteriosis and trichomoniasis. Cattle cannot be
derived from a property on which Johnes disease (Mycobacterium
paratuberculosis) has been diagnosed within the previous 5 years. In
addition, they must have negative tests for paratuberculosis. Cattle
must also be free of antibodies to enzootic bovine leukosis, and the
property must have a history of freedom from the disease. All of
these diseases are listed as "B" or "Others" on the OIE disease lists
(discussed below). Once the animals are in the fully health-tested
area of the licensed center, they must undergo annual testing for
freedom from the above-mentioned diseases.
Semen production centers in Australia must comply with the Aus-
tralian and OIE standards to be eligible to export semen. By defini-
tion, a licensed bovine semen production center is licensed under
state legislation to produce semen for sale from bulls kept within the
center and judged to be disease free according to the minimum stan-
dards described by the Australian Quarantine Inspection Service (1988~.
Similar requirements are laid out in regulations governing AB
centers in the United States, Canada, Great Britain, and New Zealand,
and they form part of the OIE standards for artificial breeding. Ad-
ditional disease control tests are required of countries in which the
diseases on the OIE's List A (discussed below) are present. Even for
many of these important disease agents, however, information on
their transmission in semen is minimal. Often, the evidence is ob-
tained during the viremic phase of the disease, when the agent is at
its highest titer in the blood. Evidence of the persistent excretion of
viruses in semen is available only for a few diseases, and it may be
OCR for page 219
Appendix C / 219
an insignificant problem, particularly when health standards and tests
are applied to donors prior to and following semen collection.
Of the diseases listed by the OIE (Hare, 1985), lists A, B. and
Others include a number of agents that have been isolated in semen
from bulls, rams, bucks, and boars. The evidence, however, is often
minimal or restricted in scope, and in some cases confusing reports
on individual agents may be given. For many infectious agents there
is an obvious need for further studies to identify their potential to
transmit disease through the genital route.
Current techniques for artificial breeding provide access to the
cervix and uterus, which is not presented normally in natural mat-
ing. It is the necessity to deliver semen through this route in many
species, or through laparoscopy in some species, that enables the
agents to bypass the immunological and physiological defenses of
the female.
CONTROL OF COLLECTION, HANDLING, PRESERVATION,
AND STORAGE OF SEMEN
Standards have been developed in many countries for donor ani-
mals and the collection and storage of semen. With the advent of
liquid nitrogen cryopreservation and the development of extender
recipes and antibiotic regimes, the quality of preserved semen has
improved. Even with all previous research and continuing improve-
ment in techniques for collection, handling, and storage, semen re-
mains a product contaminated with microorganisms. Further attempts
to reduce the level of contamination have concentrated on the health
of the donor animals, their freedom from specific diseases, and as far
as possible, asepsis during collection and subsequent handling of se-
men. The latter includes ensuring the sterility of extender liquids
and the addition of a suitable antibiotic cover. Because of the need to
remove or control mycoplasmas, the antibiotic cover has now been
changed in many countries and will soon become a standard compo-
nent of semen for international use. In the United States, the use of
penicillin, dihydrostreptomycin, and polymyxin B sulphate has been
replaced in the minimum requirements of the Certified Semen Ser-
vices (CSS) with the new combination of tylosin, gentamicin, linco-
mycin, and spectinomycin (soak, 1986~. The change to the use of
this antibiotic combination has shown that processing procedures,
extender composition, and antibiotic combinations may affect the ef-
ficacy of microbial control or fertility.
The CSS has listed the following requirements (soak, 1986~:
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220 / Appendix C
Extender must be of a type approved by the CSS.
Contact between antibiotics and raw semen must be for less
tin 3 minutes.
· Cooling of semen and nonglycerol fraction of less than 2 hours
to 5°C.
Glycerol cannot be added as an extender component until
after cooling to 5°C.
The new antibiotics and procedures have been accepted in the
United States for intra- and interstate movement of semen for artifi-
cial breeding. International movement of semen will require export-
ing countries to comply with the changes. Many countries outside
the United States are moving to adopt similar changes (Shin, 1986),
and such changes may be adopted as part of the quarantine protocols
for international movement of germplasm.
MAJOR DISEASES OF CONCERN IN ARTIFICIAL BREEDING
List A Agents
The major diseases of concern in the international transfer of ga-
metes for artificial breeding are mostly those caused by viruses. The
JOE's List A Agents are communicable diseases that (1) have the po-
tential for very serious and rapid spread irrespective of borders, (2)
are of serious socioeconomic or public health consequences, and (3)
are of major importance in the international trade of livestock and
livestock products (Gibbs, 1981; Hare, 1985; Odend'hal, 1983; Parez,
1985~. Some of these diseases are described below.
Foot-and-Mouth Disease Virus
The most important virus disease on the OIE's List A is that caused
by the foot-and-mouth disease virus (FMDV) because of its presence
on all continents, except Australia and North America, and because
of the number of animal species affected by FMDV. Cottral et al.
(1968) identified the presence of FMDV in semen of bulls and its
subsequent transmission by artificial insemination. This finding was
confirmed by Sellers et al. (1968), who also showed that bulls ex-
posed by indirect-contact infection had high titers of FMDV in the
semen before the lesions of clinical disease appeared. These findings
precluded the use of semen from FMDV-infected countries for a number
of years. As new testing systems were developed, protocols were
also developed by some countries to allow international movement
OCR for page 221
Appendix C /221
of semen. Acceptance of these protocols has enabled considerable
headway to be made in relation to other disease agents on List A,
such as bluetongue virus (BTV).
Bluetongue Virus
BTV can infect a wide range of ruminant species. During the
past 10 years, research into the excretion of BTNI in bovine and ram
semen has shown that, in the vast majority of cases, BTV is only shed
during the period of viremia, and then at a titer that is considerably
lower than in the blood (Bowen et al., 1983; Breckon et al., 1980;
Parsonson et al., 1981b, 1987a,b). When semen contaminated with
BTV is instilled into the cervix and uterus of susceptible cattle, it
usually causes infection, generally without clinical signs, and it ap-
pears to have little or no effect on subsequent pregnancy (Bowen and
Howard, 1984; Parsonson et al., 1987a,b). However, when cattle were
experimentally infected with insect-passaged (Culicoides variipennis)
BTV serotypes 11 and 17, congenitally deformed calves were pro-
duced (Luedke et al., 1977~. Similar experiments have not produced
infected calves, nor was serological or virological evidence of trans-
placental transfer of BTV found in those studies (Parsonson, 1990;
Parsonson et al., 1987b). In a study in which bovine fetuses were
inoculated in utero with BTV at 125 days gestation, MacLachlan et al.
(1984) showed that the virus did not persist in the fetus at birth.
Thus, fetuses infected in utero are unlikely to be reservoirs for the
virus.
Additional studies on the fetal transmission of BTV seem unnec-
essary in light of the mounting evidence against transmission by this
route. There is need, however, for further studies of the initial repro-
ductive stages in sheep and cattle to ensure that BTlI is not a cause of
reproductive losses in endemic areas. Despite the experimental evi-
dence, Osburn (1986) suggested a need for further studies in dairy
cattle in California.
Rinderpest Virus
Although rinderpest virus can infect a wide range of ruminant
species, there is very little evidence for its spread through artificial
breeding. Scott (1964), however, reported isolation of the virus from
all secretions and excretions of infected animals, and Plowright (1968)
cited Curasson (1921) and lacotot (1931) as finding the virus in vagi-
nal secretions for 5 to 12 weeks after abortion had occurred. Because
rinderpest and peste des petite in ruminants cause obvious disease
OCR for page 222
222 / Appendix C
on a herd basis, it is unlikely that semen or ova for artificial breeding
would be collected from animals in an area where an outbreak has
occurred.
In an extensive series of tables, Scott (1964) has detailed animal
species known to be infected with rinderpest virus. The lists are
important when considering species that are endangered or at risk.
Lumpy Skin Disease (Neethling Virus)
In experimentally infected animals, Weiss (1968) demonstrated
the presence of lumpy skin disease virus (LSDV) in bull semen for 22
days following fever and generalized skin lesions. Weiss, however,
also demonstrated the presence of virus in semen at days 7 and 12 in
bulls undergoing inapparent infections. Almost certainly, virus would
be present in secretions of cows from which embryos were collected
during infection. The similarity between LSDV and capripox has
been noted in several reports, and LSDV has been classified in the
genus Capripoxvirus by Penner (1976~.
Sheep and Goat Pox Virus
These viruses were originally thought to be species specific. However,
Kitching and Taylor (1985), however, have shown a close serological
antigenic relationship, and cross-protection studies have supported that
firlding. As a result, Kitching and Taylor have suggested that the term
capripox be used in the future, irrespective of the species involved.
Because of the similarities between these viruses and LSDV, ex-
cretion in both semen and vaginal discharges are extremely likely
during infection of donors. Because collection of semen or ova would
be unlikely during the occurrence of clinical disease, there should be
little chance of venereal transmission. This group of viruses is ex-
tremely resistant to environmental factors, however, and all precau-
tions to avoid venereal transmission must be taken. A suitable at-
tenuated virus vaccine for capripox, the 0240LT/1 BHK/2 LT/4 strain
of Kenyan sheep and goat pox virus, has been shown to be stable and
safe and to provide substantial protection for at least 1 year (Kitching
et al., 1987~. Semen and embryos could therefore be collected from
donor animals vaccinated against Capripoxvirus.
Rift Valley Fever Virus
Rift Valley fever virus (RVFV) is an arthropod-borne virus that
can also be spread by contamination of the environment and by aero
OCR for page 223
Appendix C / 223
sots. It is a particularly difficult agent to control. Vaccination is
carried out in some areas of the African continent where epizootics
have occurred and in endemic areas where sporadic outbreaks cause
problems to livestock. Although R~FV causes abortions in pregnant
animals of many species, including humans, and although it can be
fatal to neonatal and young animals, there is a paucity of information
on its effect on reproduction. This lack of information may be related
to the severity of the clinical condition and the insignificant role that
reproductive disorders would play in an outbreak of the disease.
However, there is a need to know how to avoid transfer of this agent
in gametes originating in endemic areas of Africa and destined for
international trade. Several wild animal species from Africa are also
susceptible, and any efforts to store gametes to preserve animal ge-
netic resources would have to take cognizance of this fact (Easterday,
1965; Meegan et al., 1979~.
Vesicular Stomatitis Virus
Vesicular stomatitis viruses (Indiana and New Jersey serotypes)
are confined to the Americas. Although some understanding of the
epidemiological behavior of the virus group is available, there are
great gaps in essential knowledge. Virtually no studies have been
carried out on transmission of the virus through the reproductive
tract.
Domestic species of animals affected by these viruses include cattle,
horses, and pigs; humans are also affected. Some wild animal spe-
cies, including deer, are affected. The virus propagates readily in
laboratory animals, such as rabbits, guinea pigs, and mice. A carrier
state for these viruses has not been demonstrated and hence, the
serological tests used by U.S. authorities to introduce zebu cattle from
Brazil (House et al., 1983) were standardized to reject recently in-
fected animals. Perhaps similar tests should be set for semen donors.
This agent is one of the remaining enigmas of veterinary science and
pathogenesis, and epidemiological studies are urgently needed be-
cause animals and gametes from the Americas constitute a large seg-
ment of international trade in livestock germplasm.
Contagious Bovine Pleuropneumonia
Contagious bovine pleuropneumonia (Mycoplasma mycoides subsp.
mycoides) is a disease of cattle present in Africa, Portugal, Spain, oc-
casionally other parts of Europe, Asia minor, some east European
countries, and China.
OCR for page 224
224 / Appendix C
Very little is known of the reproductive disorders caused by this
microorganism. In studies carried out in Australia before the disease
was eradicated in 1968, there was no indication of semen contamina-
tion, nor of intrauterine infection of the fetus (Seddon, 1965~.
Swine Vesicular Disease Virus
Swine vesicular disease virus (SVDV) and (FMDV) have both been
isolated from boar semen. Sows inseminated with SVDV seroconverted
(McVicar and Eisner, 1977), thus demonstrating the potential to transmit
SVDV infection through this route. Although difficulty with mount-
ing was seen in boars affected with FMDV, it may not prevent collec-
tion of semen contaminated with FMDV or SVDV before manifesta-
tion of clinical disease (McVicar, 1984; Thacker et al., 1984~.
African Swine Fever Virus
African swine fever virus (ASFV) has been described as causing a
highly contagious, fatal disease in domestic pigs, but it also can be
manifested as a mild to moderately severe disease, almost indistin-
guishable clinically from hog cholera. The virus is present in Africa,
Italy, Portugal, Sardinia, and Spain. At present, ASFV appears to
have been eradicated from parts of South America and the Carib-
bean. A report that ASPS, present in cryopreserved semen collected
during viremia from an experimentally infected boar, was transmit-
ted to a recipient female and produced infection (Schlafer, 1983) indi-
cates the need to treat semen as a possible source of infection with
this agent.
Hog Cholera Virus
Successful eradication programs in several countries have reduced
the incidence of hog cholera virus (HCV) in herds of pigs. Because
the most serious chronic manifestations of HCV are on reproductive
conditions, including fertility, abortions, teratogenic defects, and neonatal
deaths, control of this disease has widespread benefits (Cheville and
Mengeling, 1969~.
Evidence that a country is free of HCV is required for interna-
tional movement of swine semen. Serological tests and disease con-
trol practices are becoming required conditions for members of the
European Economic Community. Outbreaks of hog cholera are still
occurring in Europe, however, as evidenced by an outbreak in the
United Kingdom (Anonymous, 1986~.
OCR for page 225
Appendix C / 225
Summary
The diseases of greatest concern in the international movement of
semen are those discussed above. Generally, the high pathogenicity
and economic risks resulting from an infection by these agents en-
sure that production of gametes for international trade will be from
countries free of these diseases. Increased risks may be involved and
may be unavoidable, however, to procure access to highly desirable
genetic material. Countries that largely depend on livestock indus-
tries have had to develop protocols to enable collection of semen and
embryos from areas where diseases on the OIE's List A occur. Be-
cause of advances in testing methods for the agents listed and better
disease controls within the countries where the agents are present,
semen and gametes from high-risk areas of Africa and South America
can now be transferred through offshore quarantine facilities to the
United States, Australia, and New Zealand. Such transfers of ga-
metes have increased prospects for international movement of animal
germplasm and also have improved prospects for cryopreservation
and use of rare, potentially desirable genetic materials.
List B Agents
The diseases on the OIE's List B are generally diseases for which
adequate test systems are available in most countries. They are con-
sidered to be of socioeconomic or public health importance within
countries and are significant in the international trade of livestock
and livestock products. Some of these agents are described below.
Bacterial and Protozoal Agents
As stated by Wierzbowski (1984), the methods of testing bulls in
artificial breeding centers for brucellosis, tuberculosis, paratuberculosis,
leptospirosis, and trichomoniasis are well established and effective.
Bartlett (1981) defined the need for uniformity of diagnostic methods
for the diseases listed above as a basis for semen derived from spe-
cific pathogen-free donors, and Wierzbowski (1984) listed the princi-
pal diseases of concern for artificial breeding. With modern diagnos-
tic tests, all the agents listed can be detected readily. For several of
the diseases, either vaccines or reasonably adequate antibiotic treat-
ment methods are available.
For campylobacteriosis, diagnostic tests that can identify carrier
bulls in AB centers are available (Clark, 1985a). A vaccine developed
in Australia can ensure eradication of campylobacteriosis from AB
OCR for page 234
234 / Appendix C
I
The cryopreservation of chicken semen from inbred and special-
.zed strains will be a vital resource for specific pathogen free elite
and grandparent flocks. Storage of semen from these sources will
provide a safeguard in the event of a change in disease status. More
important, however, it will provide a valuable genetic library for the
future. Studies by Sexton (1979), Lake et al. (1981), Lake (1986), and
Bacon et al. (1986) have established the possibilities for long-term
cryopreservation of chicken semen. Established methods for artifi-
cial breeding of poultry will enable storage of inbred and elite lines
of chickens and other birds, including endangered wild species.
ARTIFICIAL BREEDING OF ENDANGERED
AND RARE SPECIES
The numbers of rare and endangered species of animals and birds
are rapidly increasing as humans move into the breeding ranges of
these species. The importance of utilizing all knowledge available
from artificial breeding to attempt the continuation of endangered
species and, where possible, the long-term preservation of their ga-
metes for posterity, is a vital issue for this generation (Durrant et al.,
1986; Mason, 1974~.
The development of animal model systems for embryo technolo-
gies for rare and endangered species of wildlife has generated great
interest among several concerned groups (Wilds et al., 1986~. The
Convention on International Trade in Endangered Species of Wild
Flora and Fauna (U.S. Department of the Interior, 1984) has recog-
nized more than 200 mammalian species as being threatened by ex-
tinction. The accelerated rate of habitat destruction is leaving conser-
vationists very little choice other than managing most wildlife in
captive situations, such as in zoological gardens or parks and wild-
life reservations. Many of the wildlife species that are threatened
require very careful, expert handling and treatment to ensure that the
techniques adopted for their preservation are suitable and not harm-
ful or stressful to their well-being.
Because of the lack of knowledge of the genetic background of
many endangered species, with respect to the size of the genetic base,
any information that is pertinent is urgently required. This also ap-
plies to reproductive technologies, including gamete collection, han-
dling, storage, and treatment. Until the information is available and
organized into developing strategies for propagation of species by
artificial means, there is little chance of using AB as a viable alterna
OCR for page 235
Appendix C / 235
five. Yet, it offers the only major hope for the preservation of many
species.
RECOMMENDATIONS FOR FURTHER RESEARCH
The OIE has set standards for the hygienic collection and han-
dling of fresh and preserved bovine semen in artificial breeding cen-
ters, appendix 5.2.1.1 (1986~. The OIE states that observation of the
standards will result in bovine semen almost free of common bacteria.
In the OIE code for bovine semen (1986) from AB centers accred-
ited for export, the purpose of official sanitary control in semen pro-
duction is to maintain the health of animals at an AB center at a
standard that permits the international distribution of semen free of
specific pathogenic organisms that can be carried in semen and cause
infection in recipient female cattle. In discussing the cryopreservation
of genetic material and the disease risks and controls, Wierzbowski
(1984) pointed out the danger of contaminated single ejaculates being
spread over a long time period. Hare (1985) emphasized the advan-
tages of semen as a disease-control method over animal-to-animal
contact. Collection of semen can be made from donors known to be
free of specific pathogens, and a statistically defined sample of any
individual collection can be tested for freedom from specific microor-
ganisms before insemination. An additional benefit is that the do-
nors can be tested for evidence of previous infection for periods of
time, extending into months if necessary, before their semen is used
in artificial breeding.
Hare (1985) elaborates on the historical development of AB cen-
ters and the development of legislative controls based on country of
origin, herds, and finally individual donors and their semen. Such
controls have become recognized internationally.
Proposals for freedom from specific pathogenic microorganisms
for bovine semen were made originally by Bartlett et al. (1976~. However,
some countries, such as Australia, already had a strict code for the
production of semen free of specific pathogens. Disease-free require-
ments are now being recommended internationally, and the disease
lists generally adopted are based on the OIE's A, B. and Other lists.
It is expected that in a member country, donor animals producing
semen will be free of diseases on List A, the AB herd should also be
free of diseases on List B. and the individual donors should be free of
diseases on the Other list (Office International des Epizooties, 1986~.
Although the OIE has been cited as having an influence on AB,
Wierzbowski (1984) has correctly suggested that the national or state
veterinary authorities should be responsible for the health status of
OCR for page 236
236 / Appendix C
AB centers producing germplasm for international trade. In addi-
tion, the Food and Agriculture Organization of the United Nations
should produce lists of suitable AB centers, with annual updates to
establish standards of quality internationally. Irrespective of the offi-
cial body that undertakes the task, continuous monitoring of the dis-
eases to be excluded and notification of newly recognized pathogenic
microorganisms would be essential to the effectiveness of such stan-
dards. The international trade in germplasm has functioned with
exceptional efficiency, based on the requirements of the importing
countries and the standards for AB centers of the exporting countries.
Only very rarely is transmission of disease in germplasm recognized
as occurring following international transfer (Kupferschmied et al.,
1986~. When such cases do occur in a country in which the disease
has been controlled or eradicated, the consequences for the disease
control authorities of the recipient country can be extremely difficult,
and the country may incur considerable financial costs in reinstitut-
ing freedom from the disease.
Diagnostic tests for many diseases likely to be transmitted by
semen are being improved, and new tests are being developed in
many laboratories engaged in this research around the world. The
problems of searching for agents in semen are manifold, however,
and have been the subject of extensive research. Such methods are
far too costly and often are grossly inefficient when compared with
testing donor animals before and after collection of semen and prior
to release of semen (Kahrs and Littell, 1980; Parez, 1984; Richmond et
al., 1977; Schultz et al., 1982~. For the majority of viral diseases in
domestic animals, there is a concurrent viremia whenever the virus is
excreted in semen, and therefore, it is preferable to test for antibodies
or virus in the blood. The recent development of technologies, such
as the polymerase chain reaction (Erlich, 1989), will enable screening
of semen and embryo samples for evidence of specific pathogens and
should enhance the confidence in international movement of germplasm.
For microorganisms present in the preputial cavity of animals
that are commonly transferred into the semen collection, other than
viral or protozoa! contaminants, the dilution of semen in extenders
tends to lower the probability of infection. In addition, the use of
antibiotics provides a control on the proliferation of bacterial and
fungal contaminants. For the diseases for which vaccination can be
used as a prophylactic measure, such as campylobacteriosis, excre-
tion of immunoglobulins into the preputial cavity enables control of
the infection. Similarly, if vaccines are used to protect against or
control general infections, secreted immunoglobulins will reduce the
possibility of semen contamination. In some tropical environments,
OCR for page 237
Appendix C / 237
the climate and the normal behavior of animals can make it difficult
to control microorganisms, for example, water buffalo and bucks in
India (Gangadhar et al., 1986; Sharma and Deka, 1986~.
In AB centers, there will always be populations of microorgan-
isms, many of which will reside in the preputial sheath and on the
surface of the penis. The aims of the OIE recommendations and the
majority of AB centers are to confine and restrict pathogenic microor-
ganisms. Many of the major bacterial diseases of concern in the first
AB centers, including brucellosis, tuberculosis, leptospirosis, campylo-
bacteriosis, and trichomoniasis, have now been eradicated or are con-
trolled, and are no longer considered problem diseases. New disease
agents have emerged, however, such as mycoplasmas, ureaplasmas,
And Haemophilus spp. In addition, some of the viral diseases not
considered previously are now recognized as potentially spread through
semen. The most important viral disease in this category is BVDV,
and some attempts are now being made to eliminate bulls carrying
this agent from AB centers in Britain (Lucas, 1986~.
Pestiviruses also cause a disease of great importance in sheep
flocks (Border disease), and thus, ram semen should be free of this
group of viruses. Bulls that have been infected in utero with BVDV
and appear clinically normal and test seronegative will frequently
excrete the virus (Littlejohns, 1982~. Although BVDV has been found
in semen (McClurkin et al., 1979), it is very difficult to culture from
semen and could be present as a contaminant. Thus, BVD seronegative
bulls in AB centers could best be checked by attempting to isolate the
virus from blood and by carrying out serological testing to ensure
freedom from BVDV.
Infectious bovine rhinotracheitis virus is known to be a contami-
nant of semen when there is a recrudescence of the disease on the
penis and prepuce of infected bulls (Snowdon, 1964; Studdert et al.,
1964~. Once bulls have exhibited penile infection, the disease can
intermittently recur with shedding of virus. Bulls that are seronegati~re
for IBR virus are the only animals which can reliably be used for the
production of semen for export (Kupferschmied et al., 1986~.
Following intranasal IBR virus vaccination of bulls and testing
large numbers of semen samples in the Cornell semen test (Schultz et
al., 1982), IBRV was not detected in the semen of IBR seropositive
bulls. The authors suggested that there may be a variation in the
excretion sites between vaccinated (intranasal) and naturally infected
bulls.
Because of the detection of bluetongue virus in the semen of bulls
(Bowen et al., 1983; Breckon et al., 1980; Luedke et al., 1975; Parsonson
et al., 1981b), and the possibility of a bull remaining persistently
OCR for page 238
238 / Appendix C
infected and excreting virus intermittently in his semen (Luedke et
al., 1975), many countries have required a seronegative status for
BTV from all donor bulls. At present, this requirement is essential to
ensure semen free of BTV. There are indications, however, that this
requirement may in fact be far too rigid and restrict access to desir-
able germplasm because experimental and field experience has not
verified the "carrier state" for BTN1 (Monke et al., 1986; Parsonson et
al., 1987b).
Bovine leukosis (BL) virus has not been found to be shed in se-
men (Schultz et al., 1982~. Monke (1986) found that seropositive bulls
infected with BLV did not transmit the virus in their semen.
Ideally, bulls at AB centers should be specific pathogen free, par-
ticularly where storing semen for long periods of time is being con-
sidered (Bartlett, 1981~. However, because not all viral diseases pro-
duce a "carrier state" in bulls, serologic evidence to show that there
has not been a rise in antibody titer, but rather that there has been a
fall in antibody titer, may be sufficient to enable collection of semen
from seropositive bulls. With BVD virus, seropositive bulls, or
seronegative bulls from whom virus could not be isolated from the
blood, could be used for the long-term storage of semen. For IBR
virus, seronegative animals are preferable, but, as Schultz et al. (1982)
showed, under some circumstances even these animals could be used.
Obviously, a specific virus free status for the important viral agents,
as is required in many AB centers in Britain (Lucas, 1986) and Austra-
lia, is the ideal status to achieve.
Within the United States, the Certified Semen Services provides a
voluntary code, Minimum Requirements for Health of Bulls Producing
Semen for A.I., for the member organizations of the National Associa-
tion of Animal Breeders to establish standards for herd health and
standards of hygiene for AB establishments (Howard, 1986~. Although
these standards are proposed for bull AB centers, the principles would
be applicable for other species of domestic animals used in artificial
breeding.
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Representative terms from entire chapter:
bovine semen
