A study on the probable causes of lowered fertility in estrous-synchronized sheep

Abstract

A study was made on the effect of synchronizing estrus in ewes with flurogestone acetate-impregnated pessaries on the reproductive efficiency relative to the stage of the estrous cycle in which synchronization was initiated. Pessaries were inserted in 36 Rairbouillet ewes on either days 2, 9, or 14 of the estrous cycle and remained in place for l4 days. Nineteen untreated ewes served as controls. Two, three or four days after breeding at the synchronized estrus all animals were evaluated on estrous response, ovulation and fertilized ova. Ovaries for hormonal assays were randomly collected from 28 animals; 3 pairs from each experimental group and five pairs from control animals on each of days 2 and 3 post-breeding. In those animals in which progestogen treatment was begun at the late follicular stage the percentage of estrous synchrony was highest, although these animals had the shortest length of estrus. The results of the Influence of the time of synchronization Initiation on fertility of ova indicated that treatment begun at the early luteal stage will cause less ova to be recovered but a higher percentage of fertility. Ewes treated at mid-cycle had the lowest percentage of fertility but the highest percentage of ova recovered. Values of 17β-estradiol, estrone and progesterone at early pregnancy were inconclusive but suggest an overabundance of estrogen which could cause the observed increase in ovum transport in animals synchronized during the early luteal stage.