Estrus in horses refers to the recurring reproductive cycle in mares during which they exhibit signs of sexual receptivity and fertility. This phase is part of the larger estrous cycle, which includes several stages: estrus, metestrus, diestrus, and proestrus. During estrus, mares experience physiological changes, such as follicular development and ovulation, which are regulated by hormonal fluctuations, primarily involving estrogen and luteinizing hormone. Behavioral changes, including increased vocalization, restlessness, and receptivity to stallions, are also observed. This page compiles peer-reviewed research studies and scholarly articles that explore the physiology, endocrinology, and behavioral aspects of estrus in horses, as well as its implications for breeding management and equine reproductive health.
Vallejo-Soto P, Dorado J, Herrera-García R, Álvarez-Delgado C, Gómez-Laguna J, Santiago Á, Manrique M, González Ariza A, León Jurado JM....Assisted reproductive techniques are often extrapolated from horses to donkeys, despite poorer fertility outcomes in jennies. This issue has been attributed to unknown uterine species-specific differences. This study compared, through histomorphometry, the endometrium of jennies and mares. Endometrial biopsies (N = 12) were taken from reproductively sound jennies (n = 6) and mares (n = 6) in estrus. Histomorphometric analysis evaluated luminal (LE, µm) and glandular epithelium height (GE, µm), glandular lumen diameter (LD, µm), glandular area (GA, µm), the number of glands (#G), and glandu...
Cui B, Liu Y, Wu X, Li X.The objective of this study was to evaluate the effects of exogenous GnRH administration at the beginning of estrus synchronisation in mares during the spring transitional period. Estrus was synchronised using a progesterone releasing intravaginal device (PRID). The PRID was left in the vagina for 10 days, followed by an injection of 0.4 mg of cloprostenol at PRID removal. The GnRH group (n = 32) was subjected to intramuscular administration of 100 μg of the GnRH agonist triptorelin at PRID insertion, while the control group (n = 32) received 1 mL of sterile physiological sali...
Donato GG, Necchi D, Gionechetti F, Ala U, Nebbia P, Robino P, Stella MC, Vandaele H, Pallavicini A, Nervo T.In the past, bacteria detected in the mare's uterus were generally interpreted as a sign of endometritis, since the uterus was considered a sterile environment. This assumption has been challenged by the introduction of culture-independent molecular techniques, particularly 16S rRNA amplicon sequencing, which have demonstrated that healthy mares harbor an endometrial microbiota. The aim of this study was to characterize the endometrial microbiota of healthy mares and to determine whether microbial composition differs between estrus and diestrus. Endometrial samples were collected from eleven h...
Cuervo-Arango J.The objective of this study was to compare the fertility of diestrous mares with a follicle ≥ 30 mm in diameter treated with prostaglandin F2α (PGF) (PGF group) or left untreated for 7 days (SP group). Standardbred mares (n = 46) were assigned randomly to the SP (n = 23) and PGF groups (n = 23) when they were identified with a corpus luteum (CL) of unknown age and a follicle ≥ 30 mm in diameter (Day 0). The most frequent outcome in the PGF group was estrus and ovulation of the dominant follicle (74 %), while the outcomes of the SP mares 7 days after Day 0 were more variable: estrus and fo...
Sala-Ayala L, Cuervo-Arango J, Martínez Boví R.Endometrial edema is an ultrasonographic sign of estrus in mares and is positively associated with fertility. This study aimed to evaluate the influence of follicular size, systemic progesterone (P4), and exogenous estradiol benzoate (EB) on the onset and duration of endometrial edema. In Experiment 1, anestrus (n = 4) and diestrus mares (n = 4) received 4 mg of EB intramuscularly; edema scores and plasma P4 were monitored over four days. In a complementary group (n = 5), mares were monitored until ovulation, then administered 4 mg of EB and examined every 12 h for 48 h. In Experimen...
