The Use of hCG for Inducing Ovulation in Sheep Estrus Synchronization Impairs Ovulatory Follicle Growth and Fertility

Abstract

Currently, there is an intense effort to find an alternative hormone to eCG to induce ovulation after estrus synchronization treatments in sheep. One of the proposed alternatives is based on the use of hCG, but the results are controversial since fertility rates are commonly affected. The present study aims to evaluate, therefore, the adequacy of hCG in protocols for the synchronization of estrus and ovulation. Ovarian follicle dynamics, occurrence of estrus behavior and subsequent ovulation, quality of corpora lutea, and pregnancy rate after controlled natural mating were assessed in two consecutive trials. The findings indicate that the low fertility rates reported for the protocols based on the administration of hCG for inducing ovulation during estrus synchronization in sheep may be related to a high occurrence of abnormal follicular growth patterns, disturbances, and retardments of ovulation and concomitant formation of follicular cysts in the treated females. These results preclude their practical application to induce ovulation concomitantly to estrous synchronization treatments.

Efficiency of hCG for Inducing Resumption of Ovarian Cyclicity and Synchronized Ovulations during the Seasonal Anestrous in Sheep

“…Such a scenario suggests that exposure to progesterone and active males was able to trigger the resumption of ovulatory response, although only in some of the animals (and in an extended period of time). Moreover, the results observed in the hCG ewes showed a lower synchronized activity when inducing estrus, ovulations and pregnancies as compared to the eCG ewes, the last in agreement with previous studies [ 17 , 24 ]. Hence, in view of these performances, the hCG treatment would not be as useful as the eCG administration when implementing artificial insemination protocols.…”

“…In spite of the lack of synchronized ovulations during the first 72 h after CIDR removal, around 85% of the hCG ewes denoted presence of ovulations on day 10 after progesterone removal, which may indicate the usefulness of hCG for inducing the resumption of the ovulatory activity of anestrous sheep, although in a narrow window of time. Our proposed treatment, based on the administration of hCG at the timing of progesterone removal, simplifies the management of the animals more than previous treatments including the administration of hCG at 24 h after CIDR removal and, therefore, one more handling day [ 17 ]. Therefore, if males remain with females for some days, it can be adopted by practitioners aiming to induce pregnancies in a short period of time.…”

“…The characteristics of hCG, mainly its high similarity to LH and affinity for the same receptors [ 12 , 13 ], favored its use for inducing ovulations when applying protocols for estrus synchronization in sheep [ 14 , 15 ]. Yet, recent studies have evidenced a decrease in fertility due to deleterious effects on the development of ovulatory follicles [ 16 , 17 ]. However, these studies were performed during reproductive season and the differences in the follicle dynamics occurring during the seasonal anestrous [ 18 ], due to the different patterns of release of LH [ 19 ], are currently well known.…”