The effects of human chorionic gonadotrophin on ovulation, length of estrus, and fertility in the mare.

The research explores the effects of human chorionic gonadotrophin (HCG) on aspects of a mare’s reproductive cycle such as ovulation, duration of estrus, and fertility rates. The study also considers variations in these cycles among different mares, with implications for improving breeding efficiency in horses.

Background and Introduction

• The researchers discuss the challenges in stimulating follicular development in mares during their reproductive cycles and particularly during anestrus (a period of sexual inactivity), noting their resistance to most gonadotrophic hormone preparations.
• An exception to this resistance is the usage of gonadotrophic preparations with primarily luteinizing activity, which can change the timing of ovulation in relation to the start of estrus – the cycle in which a female animal is sexually receptive.
• As timing from the start of estrus to ovulation is variable and difficult to predict accurately in mares, this variability contributes greatly to inefficiencies in horse breeding practices.

Ovulation and Estrus

• The report cites several previous studies showing that ovulation is closely linked to the end of estrus, typically occurring 24 to 48 hours prior to cessation of estrus.
• However, the duration of estrus can vary considerably from one mare to another, and there isn’t much evidence of its consistent length within individual mares. This randomness adds difficulties to the prediction of ovulation’s occurrence and the optimal timing of breeding.

Human Chorionic Gonadotrophin (HCG)

• The usage of human chorionic gonadotrophin (HCG) to prompt ovulation at a predictable time during estrus was initially put forward by Russian researchers in the 1930s. This method allows for improved timing of breeding and thus, increases breeding efficiency.
• Compared to other gonadotrophins, HCG has been found to be more reliable for inducing controlled ovulation. However, despite its benefits, this technique is not commonly used in standard breeding operations supervised by veterinarians.

Research Purpose and Preliminary Results

• The researchers aim to explore the potential of using HCG in mares to reduce variability in ovulation and improve breeding practices.
• The preliminary results from their usage of HCG in their lab have yielded partial success and their findings have formed the basis of the partial report within this article.