Estrus, Ovulation and Conception following Synchronization with Progesterone, Prostaglandin F2α and Human Chorionic Gonadotropin in Pony Mares

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Abstract
In experiment 1, 72 pony mares were assigned randomly to an experiment of 3 × 6 factorial design (four mares/group) in which treatments were: controls, no injections (C); progesterone daily, 50 mg IM, days 0 through 18, plus HCG, 2,000 IU SC, 6 days later (P-HCG); prostaglandin F2α, 1.25 mg IM, days 0 and 18 only, plus HCG, 2,000 IU SC, 6 days following the last PGF2α injection (PGF2α-HCG). Treatments were initiated on day 2 of estrus or days 1, 4, 7, 10 or 13 post-ovulation. There was no significant (P>.05) effect of day of cycle on which treatment began or treatment by day interaction on interval from day 18 to ovulation. Thus, data pooled over days indicated interval to ovulation was shorter (P<.05) for both P-HCG (8.5 ± .4 days, mean ± SE) and PGF2α-HCG (8.9 ± .8) treated mares than controls (12.8 ± 1.4). Although there was no difference between means for both treated groups there was greater variance (P<.01) in interval to ovulation following treatment with PGF2α-HCG than P-HCG. Mean size of largest follicle was greater (P2α-HCG (22.7 ± 2.5 mm) treated mares; 11 of 21 P-HCG and six of 23 PGF2α-HCG treated mares ovulated within 2 days following HCG. Four of 21 P-HCG and six of 23 PGF2α-HCG treated mares ovulated before HCG treatment. Initial treatment with PGF2α did not result in return to estrus or ovulation before the second PGF2α injection in three of four and one of four mares which were treated on days 1 and 4 post-ovulation, respectively. Results indicate that better synchronization of ovulation occurred after the P-HCG regime than after the PGF2α-HCG regime. In experiment 2, a combination progesterone -PGF2α-HCG regime was followed by a single breeding (SB) or multiple breedings (MB) to determine pregnancy rate. Sixty pony mares were assigned randomly, without regard to stage of the estrous cycle, to three groups (n= 20). Controls were given no injections while treated mares received progesterone (75 mg, IM) for 10 days in addition to PGF2α (1.25 mg, IM) on day 7 during progesterone treatment, and HCG (2,000 IU, SC) 5 days following progesterone. Controls were bred by artificial insemination with 10 ml fresh whole semen every other day while in estrus. Mares in one treated group (MB) were inseminated every other day during the post-treatment estrus, while another group (SB) was inseminated only once one day after HCG. Pregnancy rate following one estrous cycle was not significantly different among the three groups (controls, 64.7%; MB, 57.8%; SB, 40%). The number of inseminations per estrus and per conception, respectively, were controls, 3.9 and6.0;MB, 3.7 and 6.4; and SB, 1 and 2.5. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.

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