The effectiveness of PGF 2α HCG and GnRH for appointment breeding of mares

Abstract

Eighteen nonlactating mares were given two injections of 10 mg PGF2α, 14 days apart, without regard to stage of estrous cycle. On day 2 of the induced estrus, mares were given either, saline, a single injection of GnRH (4.5 mg) or three injections of GnRH, 1.5 mg every 2 hours. More (P < .05) mares exhibited estrus after the second PGF2α injection (76.5%) than after the first (41.2%). Single or multiple injection(s) of GnRH on day 2 of estrus were ineffective in shortening the duration of estrus. In a second experiment, 54 mares were assigned to a 3 × 3 × 2 factorial experiment. Factors included: hormonal treatments — saline injection on day 0 and 14, PGF2α(10 mg) on day 0 and 14 followed by'HCG (3,300 IU) on day 19 and PGF2α (10 mg) on day 0 and 14 followed by GnRH-A (500μg) on day 19; frequencies of insemination — once only, every other day and daily; and rectal palpation-palpated and nonpalpated. More (P < .005) PGF2α — treated mares exhibited estrus after the second injection than saline-treated control mares (80.6 vs 27.8%). Of those mares responding to the PGF2α treatment, the mean interval from the second injection to estrus was 3.3 days. During the first estrous cycle after treatment, fewer (P < .05) PGF2α -treated mares became pregnant than saline-treated controls. Pregnancy rates after the second and third cycles and overall were similar (P > .05) among groups. After cycle 1, pregnancy rates were similar (P > .10) for mares inseminated at the various frequencies. After three estrous cycles, more (P < .05) mares inseminated every other day and daily became pregnant than those inseminated once only per cycle. Two injections of PGF2α given 14 days apart were effective in inducing estrus in 80.6% of the mares. After such treatment, mares should be presented to a stallion daily, beginning on day 14, to determine sexual behavior and inseminated daily or every other day during estrus.