Effects of nutritional cues on the duration of the winter anovulatory phase and on associated hormone levels in adult female Welsh pony horses (Equus caballus)
1 INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
2 CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
3 Université François Rabelais de Tours, F-37041 Tours, France
4 IFCE, F-37380 Nouzilly, France
5 INRA, UMR1198 Biologie du Développement et Reproduction, F-78352 Jouy-en-Josas, France
6 ENVA, F-94704 Maisons Alfort, France
Reproductive Biology and Endocrinology 2011, 9:130 doi:10.1186/1477-7827-9-130Published: 29 September 2011
Mares have an annual reproductive rhythm, with a phase of inactivity in midwinter. The aim of this study was to determine the impact of food restriction on physiological and metabolic hallmarks of this rhythm.
Over three successive years, 3 groups of 10 mares were kept under natural photoperiod. A 'well-fed' group was fed to maintain the mares in good body condition; a 'restricted' group received a diet calculated to keep the mares thin and a 'variable' group was fed during some periods like the 'restricted' group and during some other periods like the 'well-fed' group, with the aim of mimicking the natural seasonal variation of pasture availability, but a few months in advance of this natural rhythm.
Winter ovarian inactivity always occurred and was long in the restricted group. In contrast, in the 'well-fed' group, 40% of mares showed this inactivity, which was shorter than in the other groups. Re-feeding the 'variable' group in autumn and winter did not advance the first ovulation in spring, compared with the 'restricted' group. Measurements of glucose and insulin concentrations in mares from the 'restricted' group during two 24 h periods of blood sampling, revealed no post-prandial peaks. For GH (Growth hormone), IGF-1 and leptin levels, large differences were found between the 'well-fed' group and the other groups. The glucose, insulin, GH and leptin levels but not melatonin level are highly correlated with the duration of ovulatory activity.
The annual rhythm driven by melatonin secretion is only responsible for the timing of the breeding season. The occurrence and length of winter ovarian inactivity is defined by metabolic hormones.