Physiological and Clinical Aspects of the Endocrinology of the Estrous Cycle and Pregnancy in Mares

Abstract

The use of advanced reproductive endocrinology can generate important economic benefits for equine breeding farms. Pregnancy in the mare involves considerable endocrine changes, which can be explained in part by the development of different structures such as embryonic vesicles, primary and secondary CL, endometrial cups and development of fetoplacental units. Both the pregnant mare and the fetus adapt to this development with unique mechanisms, such as alterations in the maternal endocrine metabolism and hormonal feedback. Since the ability to produce a viable foal is critical for the broodmare, the maintenance of the gestation implies almost a year of physiological effort. Therefore, the joint knowledge of basic reproductive science and current clinical endocrinology allows veterinarians and breeders to be better positioned to achieve their objectives. This chapter reviews normal and abnormal endocrine patterns during the equine estrual cycle, pregnancy. We also consider hormonal evaluation related to placentitis, abortions, recurrent pregnancy loss, and premature deliveries. Also, several aspects associated with endocrinological control of the reproductive cycle, ovulation, parturition, high-risk mare, and hormone supplementation will be developed.

Comparison of the efficacy of altrenogest versus transdermal progestin patches on estrus synchronization and ovulation in mares

“…According to a previous report by Crabtree [ 18 ], the reproductive cycle of the horse species is endogenously cyclical, controlled by photoperiod, and synchronizes with the spring. In addition, the start of estrus after synchronization was identical in both groups and according to the onset of mare estrus following synchronization by PGF 2α [ 19 ].…”

Fertility restoration of racing mare with persistent corpus luteum

“…The percentage of mares that showed estrous signs on day 2 was 36.36% (4/11), and those on day 3 were 63.63% (7/11), on an average of 2.6±0.5 days post-PGF2α treatment (Table -2). The onset of mare estrus after PGF2α was 2.5 days [20], and ovulation occurred 8.4 days following PGF2α treatment [6].…”

“…The endogenous P4 concentrations of >4.0 ng/mL are considered adequate to maintain pregnancy. Mares with P4 concentrations <4.0 ng/mL were at risk of pregnancy loss [20]. The high P4 concentrations were vital for inhibiting myometrium contraction [30] because the connection between the trophoblast layer of the allantochorion and the endometrium's luminal epithelium was less stable before day 40 of pregnancy [31].…”

Comparative reproduction of the female horse, elephant and rhinoceros: implications for advancing assisted reproductive technologies

“…3 ). While extensive literature is available for the mare (as reviewed by Satué & Gardon 2020 ), only relatively recently did we understand the reproductive physiology of the elephant (as reviewed by Hildebrandt et al 2011 ) and rhinoceros (as reviewed by Roth 2006 , Stoops et al 2016 ) in more detail. The most relevant aspects are summarised in Table 2 and briefly described here.…”