Haemorrhage into the dominant follicle during the reproductive season is a subtle but definitive cause of infertility in the mare population. This condition however can be of high relevance for an individual in which its incidence is abnormally high. Little is known about the nature and factors affecting the incidence of haemorrhagic anovulatory follicles (HAFs) in the mare. The objectives of the study were to define and characterize the ultrasonographic development and incidence of HAFs and to investigate possible risk factors influencing its occurrence. Detailed reproductive and ultrasound records of seven mares studied during their entire reproductive lives (>10 years and 612 oestrous cycles) were analysed retrospectively and computed into a statistical mixed model. Of all animal studied, two mares were found to have an unusually high incidence of HAFs of approximately 25%. Time of season and use of induction treatments (Cloprostenol) were found to influence its incidence. It appears that early-enhanced stimulatory effect of LH on an ovary with the presence of small and immature follicles might increase the risk of ovulatory failure of those follicles later in the cycle. Mares during the months of highest follicular activity (May to August) and after treatment with hormones to induce oestrus and ovulation are at greater risk to develop HAFs. The potential relevance of this study is two folds: clinical relevance for the practitioner to better understand this condition and so improve reproductive management of mares with abnormally high incidence; and to provide useful insights for researchers willing to further investigate the nature of this phenomenon.

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Follicular diameter is used as a guiding tool to predict ovulation in the mare. However, the great range in preovulatory follicular diameter makes prediction of optimal breeding time based on follicular diameter unreliable. Uterine edema pattern is also useful to determine the best time to breed, since intensity of edema tends to dissipate as ovulation approaches, however, not every mare follows this pattern. The aims of this study were to assess the repeatability of preovulatory follicular diameter and uterine edema pattern in two consecutive spontaneous cycles and to determine how induction treatments (hCG, PGF(2)alpha and GnRH analogues) influence them. Fifty-three mares were followed during two consecutive cycles and scanned three times a day from 2 to 3 days before ovulation. During the first cycle, mares had a spontaneous ovulation and in the consecutive cycle mares received either: (a) no hormonal treatment; (b) 1500 IU hCG; (c) 125-250 microg Cloprostenol or (d) 2.1 mg Deslorelin implant. Mares ovulated consistently from similar follicular diameters in two consecutive spontaneous cycles (r=0.89; P<0.000). All three induction treatments had a significant effect on reducing the preovulatory follicular diameter (P<0.005). Mares showed fair correlation in uterine edema patterns in both consecutive non-induced cycles (r=0.71; P<0.005). In conclusion mares in consecutive cycles ovulated from consistent follicular diameters. Follicular diameters recorded from previous ovulations can be relied on to predict the optimal breeding time in successive cycles especially in mares that ovulate from unusually small follicles.

Prostaglandin F(2α) and its analogues (PGF) are widely used in equine reproductive practice. The interval from PGF treatment to ovulation (ITO) varies greatly with a range from 2 to 16 days. Clinical observation suggests that mares mated and ovulated soon after PGF treatment may have poor fertility. Reproductive records of 329 cyclic Thoroughbred mares were analysed retrospectively. The following parameters were analysed: (i) use of cloprostenol; (ii) ITO and (iii) number of ovulations per cycle. According to these parameters, mares were classified into four groups. (i) mares with spontaneous ovulations, n = 57; (ii) mares induced with cloprostenol and ITO = 4-7 days, n = 77; (iii) ITO = 8-10 days, n = 89 and (iv) ITO = ≥ 11 days, n = 106. Differences in pregnancy (PR) and multiple ovulation (MO) rates among groups were tested using chi-squared test. PR rates for groups 1-4 were: 73.7%, 46.7%, 64% and 71.7% respectively (p < 0.05). Groups 1 and 2 had lower (p < 0.05) MO rate (24.6% and 20.8%) than groups 3 and 4 (40.4% and 44.3%). It appears that ovulation soon after PGF-induced luteolysis is detrimental to PR rates. It was found highly significant that in cloprostenol-treated mares, the MO rate was enhanced without subsequent increase in multiple pregnancies.