THE SYNCHRONIZATION OF OESTRUS IN CATTLE WITH PROGESTAGEN-IMPREGNATED INTRAVAGINAL SPONGES

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Abstract
Two experiments were conducted to determine the efficacy for synchronization of estrus and ovulation in cattle of 17 [alpha]-acetoxy-9[alpha]-fluoro-ll[beta]-hydroxyprogesterone (''Cronolone'') administered by daily intramuscular injections or by intravaginal sponge. In Experiment 1, cylindrical sponges were retained in 69.4% of heifers, while in Experiment 2 ''bunched* sponges were retained in 82.8% of cows. Daily intramuscular injection of 2 mg or insertion of intravaginal sponges containing 100 mg, blocked estrus and ovulation in the majority of animals. Within 5 days of termination of treatment in Experiment 1 estrus occurred in 65.0% of heifers after intramuscular treatment and 55.6% after intravaginal treatment, while 53.5% of cows in Experiment 2 were estrous within 7 days of sponge withdrawal. Synchronization of estrus appeared more precise after intravaginal than intramuscular treatment in Experiment 1, but this was not significant. Of the estrous animals, 95% of heifers (Experiment 1) compared with 56.5% of cows (Experiment 2) were estrous 1 1/2 to 2 1/2 days after termination of intravaginal treatment. In Experiment 1, heifers were inseminated late in estrus, resulting in a pregnancy rate 8 weeks after insemination of 53.8% of estrous heifers following intramuscular treatment and 30.0% following intravaginal treatment (difference not significant). In Experiment 2, cows were inseminated 24, 36, 48, 60, 72 or 84 hr. after withdrawal of sponges regardless of the occurrence of estrus. Twelve to 15 weeks after insemination the pregnancy rate was 23.0% for estrous cows and 18.6% for non-estrous cows (difference not significant). There was a significant (P< 0.05) quadratic effect of time of insemination with the highest pregnancy rate in cows inseminated 48 and 60 hr. after withdrawal of sponges (30.6 and 29.2%). Insemination of cows 24 hr. before observation of estrus resulted in a pregnancy rate equal to that obtained from inseminations 0 to 12 hr. after observation of estrus. This is suggestive of early ovulation relative to time of estrus or an abnormal pattern of sperm transport. Whilst ''Cronolone'' impregnated sponges are quite effective in suppression of estrus and ovulation, the occurrence of estrus and the fertility to insemination after treatment are unsatisfactory and not superior to those reported after intramuscular injection or feeding of progestagens.