Effects of reproductive status and management on cortisol secretion and fertility of oestrous horse mares

Abstract

Stressful events may contribute to low reproductive efficiency due to glucocorticoid-mediated inhibition of hormone secretion in a variety of species. We therefore investigated effects of stress related to management of mares around artificial insemination on secretion of cortisol and fertility parameters. To avoid further disturbance of mares by frequent blood sampling, faecal cortisol metabolites (fCM) were determined instead (sample collection at 8-h intervals). A total of 50 mares (16 maiden, 17 barren, 12 foaling, 5 teaching mares) were included in the study. Mares were brought to the AI centre in vans or trailers (driving time between 30 min and 5 h). Teaching mares were housed in the clinic and had therefore not to be transported. Mares were inseminated either with fresh/cooled-shipped or frozen semen. Rectal palpations and ultrasound examinations were performed at 24- to 48-h intervals, in animals inseminated with frozen semen at 6-h intervals during the last 48 h before ovulation. In maiden, barren and foaling mares, fCM concentrations in faeces tended to be higher than in teaching mares at all times after arrival at the AI centre. At 24 and 48 h after arrival, fCM concentrations in maiden mares were significantly higher than in teaching mares (24 h: maiden mares 12.3 ± 3.1 ng/g, barren mares 8.5 ± 1.2 ng/g, foaling mares 11.0 ± 2.4 ng/g, teaching mares 3.8 ± 0.6 ng/g, p < 0.05). The time from arrival at the AI centre to detection of ovulation did not differ among the different groups of mares and was 4.5 ± 0.4, 5.0 ± 0.5, 3.8 ± 0.5 and 5.6 ± 0.9 days in maiden, barren, foaling and teaching mares, respectively (n.s.). Pregnancy rates were 53, 53, 55 and 60%, respectively (n.s.). The time from arrival at the AI centre to detection of ovulation was 4.4 ± 0.3 days and 4.9 ± 0.3 days in mares inseminated with fresh/shipped ( n = 39) or frozen semen ( n = 11; n.s.), respectively. The frequency of follicular checks influenced fCM secretion and was statistically significant at 16 h before ovulation (fresh/shipped semen: fCM 6.9 ± 0.7 ng/g faeces, frozen semen: fCM 16.9 ± 5.2 ng/g faeces, p < 0.01). In the mare, gynaecological examinations seem to act as stressors and may increase cortisol secretion. However, this does not negatively influence fertility and in animals familiar with that procedure fCM concentrations are not elevated.