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)

Abstract

BackgroundMares 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.MethodsOver 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.ResultsWinter 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.ConclusionsThe 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.

Blood Levels of Selected Metabolic Factors, Cytokines, and Lymphocyte Subpopulations in Arabian and Thoroughbred Horses During the Longest and Shortest Days of the Year

“…Salazar-Ortiz et al [1] reported that the mean glucose concentrations of Welsh pony mares were affected by the season, which was consistent with our results. However, in contrast with the assertion of SalazarOrtiz et al [1], in the present study, the effects of both day length and gender on glucose levels suggest that glucose is an important factor for the metabolic and reproductive activity in the horse as in other species. In addition, our results suggest that elevated glucose level in the short days of the winter months is an important adaptation for winter survival under natural conditions in the horse [28].…”

“…In the adult horse, season and nutrition are two main factors in regulation of annual reproductive activity [1]. When food availability and environmental temperature decrease during winter, physiological adaptations, including changes in reproductive and immune functions, have evolved among animals to cope with this energy restriction.…”

“…It has been reported [5] that a number of mares that have good body condition score show ovulation continuously throughout the year, suggesting that nutrition and nutritional factors such as leptin and insulin interact with season to synchronize the annual reproductive activity. For this purpose, investigation of season-related quantitative characterizations of nutritional factors including glucose, leptin, insulin, and insulin-like growth factor-1 (IGF-1) are important in determining physiological mechanisms underlying nutritional status and reproductive activity [1].…”

Condição corporal e atividade reprodutiva de eguas

“…Algumas destas éguas podem inclusive demonstrar sinais comportamentais de estro, tais como a abertura dos membros posteriores, micção e eversão do clitóris, quando expostas ao garanhão. No entanto, éguas em boa condição corporal mantêm alguma atividade ovariana e a maioria delas apresentam ciclos estrais durante os meses de inverno (Gentry et al, 2002ab;Ferreira-Dias et al, 2005;Vecchi et al, 2010;Salazar-Ortiz et al, 2011).…”

Significant differences in fertility between dairy cows selected for one QTL located on bovine chromosome 3 are not attributable to energy balance, although eating behaviour is affected

“…NEFA and glucose were determined by enzymatic colorimetry on a multiparameter analyser (KONE instruments corporation, Espoo, Finland). Plasma insulin was measured by RIA from 100 ml of undiluted plasma as previously described (Salazar-Ortiz et al, 2011). All samples were analysed in a unique assay and the coefficient of variation for a sample at 1.25 ng/ml was 6%.…”