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Recent studies associate obesity and insulin resistance in horses with development of abnormal reproductive function and debilitating laminitis. The factors contributing to insulin resistance in obese horses are unknown. However, human studies provide evidence that elevated inflammatory cytokines such as tumor necrosis factor alpha (TNFalpha), IL1, and IL6(More)
The reproductive tracts of nine thoroughbred mares were examined by ultrasound to determine the day of ovulation (day 0). Mares were fitted with intercavernous sinus cannulae on the day before the start of sample collection of pituitary venous effluent rich in oxytocin. Intercavernous sinus blood samples were collected for at least 36 h at 5 min intervals(More)
In a variety of species, short-term feed restriction leads to rapid changes in the reproductive axis and reduces serum levels of leptin. Two experiments were performed to test the hypothesis that a single day of feed restriction in aged and young mares would cause a suppression of the gonadotropins and serum leptin concentrations. The estrous cycles of 12(More)
The effects of dietary energy and recombinant bovine somatotropin (bST) on pattern of LH release, follicular development, and onset of puberty were studied in 40 Angus heifers. At 7 mo of age, heifers were assigned to a 2 x 2 factorial experiment; the main effects were dietary energy (high [HDE]: 14.15 Mcal of ME/d or moderate [MDE]: 10.84 Mcal of ME/d) and(More)
Peripheral clocks receive timing signals from the master mammalian pacemaker in the suprachiasmatic nucleus (SCN) and function to adaptively anticipate daily changes that influence local physiology. Evidence suggests that peripheral immune activation may act as a resetting signal for circadian clocks in peripheral tissues. We wished to investigate whether(More)
Daily determinations of FSH and prolactin in plasma were made for 10-12 weeks after parturition in ewes which lambed either in the middle of (December) or late in (February) the breeding season. Fluctuations in the plasma concentrations of FSH could not be related to the time after parturition or to the occurrence of otherwise of oestrus and ovulation.(More)
A transient increase in serum progesterone concentrations (to 1 ng/ml for 1-2 days) is observed in the majority of ewes before the first estrous cycle of the breeding season. To determine whether such a brief antecedent rise in progesterone ensures initiation of a full-length cycle by the next LH surge, synthetic GnRH was administered for 3 days to 24(More)
The objectives of this study were to compare the timing and mechanisms controlling the onset of anestrus in young and mature mares treated either continuously with melatonin and in those that remained untreated. Changes in body weight, subcutaneous body fat measured to provide an estimate of total body fat, and circulating concentrations of leptin were(More)
In mares, obesity is associated with continuous reproductive activity during the non-breeding season. To investigate the effect of obesity and associated alterations in metabolic parameters on the oestrous cycle, two related studies were conducted. In Experiment 1, obese (body condition score > 7) mares were fed ad libitum or were moderately feed restricted(More)
This study investigated the hypothesis that for a subpopulation of horse mares continuation of estrous cycles during the nonbreeding season may be attributed to continued stimulatory glutamatergic activity on GnRH-secreting neurons. The gonadotropin response to the glutamatergic agonist N-methyl-DL-aspartic acid (NMA) was compared in cycling and anestrous(More)