Medically Assisted Conception An Agenda for Research (1989) / Chapter Skim
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Responses to Gonadotropins in Domestic Animals
Responses to Gonadotropins in Domestic Animals
Pages 130-154
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From page 130... ...
programs have in common the use of large doses of gonadotropins to "persuade" additional follicles to grow to preovulatory size and to produce fertilizable oocytes that will develop into normal young. It has been known since the 1940's that both pituitary gonadotropins, LH and FSH, interact with the developing preovulatory follicle and are essential to its growth and differentiation (Fevold, 1941; creep et al., 1942; Fraenkel-Conrat et al., 1943~.
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From page 131... ...
Therefore, its effects as a superovulating treatment are probably due to its capacity to mimic the actions of both pituitary gonadotropins. The advantage of PMSG in superovulation of domestic animals is that it can be given as a single injection to produce multiple ovulations several days later.
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From page 132... ...
Normal estrous cycles can vary in length from around 18-26 days and, in contrast to the situation in humans, it is the luteal phase that is the most variable. Therefore, current superovulatory regimens with PMSG or pituitary gonadotropins include the injection of prostaglandin F2a (PGF;a)
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From page 133... ...
(1983) have reported that ovulation rate remained the same over the course of ten superovulations, but the number of fertilized eggs declined.
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From page 134... ...
Variability among gonadotropin preparations, even from the same supplier, may explain part of the variability observed in different superovulation trials. Murphy et al (1984)
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From page 135... ...
Several investigators have concluded that preparations with low ratios of FSH to LH give poorer superovulatory responses. Several investigators have tested this idea by using highly purified FSH and adding known amounts of AH to it in attempts to determine the optimum FSH/LH ratio (Chupin et al., 1987; Donaldson and Ward, 1986; Murphy et al., 1984~.
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From page 136... ...
A number of studies since that time have demonstrated that ewes can be synchronized by treatment with progestagens, and multiple ovulations readily induced by a single injection of PMSG given one day before the end of progestagen treatment or by multiple injections of pituitary extracts (see Wright et al., 1981 for references)
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From page 137... ...
Horses are seasonally polyestrus; their estrous cycles average 21-22 days in length and consist of a period of diestrus for about 15 days following ovulation, followed by an estrous period that averages about 7 days (Ginther, 1979~. The mare is unique among the domestic animals in having an estrous period that is long and variable in length, lasting 2-12 days (Ginther, 1979~.
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From page 138... ...
Treatment with these gonadotropin preparations for 5 to 7 days during the breeding season has also induced multiple ovulations. Treatment with FSHP in two studies resulted in ovulation rates of 1.6 and 1.7 ovulations per mare (Irvine, 1981; Squires et al., 1986)
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From page 139... ...
Finally, many purebred organizations are conservative and stud-book regulations prohibit most artificial techniques for reproduction. However, there is a need to understand better the regulation of follicular development in mares in order to develop better treatments for infertility and because the development of methods for superovulating mares could be of particular benefit in preserving and increasing numbers of individuals in endangered equine species, through transfer of embryos to recipients of similar but non-endangered species.
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From page 140... ...
Although gonadotropin treatments have been used to ensure and time follicular development and ovulation, they have not been used to significantly enhance the already high ovulation rate of pigs. Recommendations For Future Directions In Research It is clear that while superovulation of domestic animals, especially cattle, has produced some spectacular successes, the current techniques have the important limitation of variable and unpredictable response.
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From page 141... ...
~ en we used these techniques to determine the pattern of follicular development through the course of the estrous cycle, the results were surprising in that they showed in all ten heifers examined a regular pattern of waves of follicuiar development that begin about every seven days (Figure 1; Sirois and Fortune, 1988) , with one follicle in each wave growing larger, while the others regress.
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From page 142... ...
It may not be possible in the near future to reliably superovulate all, or even most, individuals in a domestic species. Therefore, it might make more sense to develop subtler approaches to hyper-stimulation - i.e., through better knowledge of critical times for gonadotropin action during follicular development, a protocol might be developed that could reliably produce 5-6 good embryos per treatment.
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From page 143... ...
-For example, one or both ovaries could be removed from a valuable heifer calf and preantral follicles obtained, grown to meiotic competence, and fertilized in vitro. The embryos could then be frozen and transferred to recipients as desired.
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From page 144... ...
First, this field is at a stalemate right now and it is hard to predict where the next big breakthrough might come. Second, it seems desirable to think in terms of different approaches for different types of animals - meiotic maturation and in vitro fertilization of thousands of oocytes from the most valuable cows, better or more reliable techniques for using gonadotropins to superovulate valuable cows, and endocrine or genetic methods for producing twins in less valuable animals.
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From page 145... ...
1944. Survival of multiple pregnancies induced in the ewe following treatment with pituitary gonadotropins.
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From page 146... ...
1974. Induction of ovulation and multiple ovulation in seasonally anovulatory mares with equine pituitary fractions.
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From page 147... ...
1978. Superovulating cows with follicle stimulating hormone and pregnant mare's serum gonadotrophin.
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From page 148... ...
1977. Induction of ovulation and multiple ovulations in seasonally anovulatory and ovulatory mares with an equine pituitary extract.
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From page 149... ...
pp. 119-127 in Follicular Growth and Ovulation Rate in Farm Animals, J
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From page 150... ...
1986. Growth and regression of ovarian follicles during the follicular phase of the oestrous cycle in heifers undergoing spontaneous and PGF -induced luteolysis.
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From page 151... ...
1986. Comparison of equine pituitary extract and follicle stimulating hormone for superovulating mares.
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From page 152... ...
TABLE 1. Superovulation An Cattle: Results fro Too Co crcial Ego Transfer Program: Hasler et al., 1983a Donaldson, 1984b # Animals 984 1,263 Mean Ova/Donor S.9 10.1 <0-70)
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From page 154... ...
T.ne asterisk indicates the last day on - ich the ovulatory follicle was observed and the dashes line shows progesterone concentrations arotmd the the of luteolysis.
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