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Item Changes in temporal leptin concentrations and other metabolic factors in primiparous, postpartum, anestrous, suckled beef cows exposed to bulls(Montana State University - Bozeman, College of Agriculture, 2009) Olsen, Jesse Riley; Chairperson, Graduate Committee: James G. Berardinelli.Exposing cows to bulls or excretory products of bulls stimulates resumption of ovarian cycling activity in postpartum, suckled, anestrous cows. This biostimulatory effect may be mediated by pheromones produced by bulls that stimulate physiological changes in metabolic regulation of the hypothalamic-pituitary-ovarian (HPO) axis of cows. In Experiment 1, the hypotheses tested were that concentrations of glucose, NEFA, thyroxine (T4), tri-iodothyronine (T3), and T3:T4 ratios do not differ between cows exposed to bulls or steers. The biostimulatory effect of bulls was associated with lower mean concentrations of NEFA in postpartum cows. Experiment 2 was designed to determine if continuous (24-h daily) bull exposure alters temporal patterns of leptin concentrations in postpartum, anestrous cows. Cows exposed to bulls that resumed cycling activity after the start of the experiment tended to have higher leptin concentrations by the end of the 30-d exposure period than cows not exposed to bulls. However, it was not known if these changes were related to resumption of ovarian cycling activity in postpartum, anestrous cows. Experiment 3 tested the hypothesis that temporal leptin concentrations may depend upon duration of daily bull exposure. Cows had higher daily leptin concentrations and resumed ovarian cycling activity sooner as duration of daily bull exposure increased. In conclusion, as duration of daily bull exposure increases, the biostimulatory effect of bulls alters temporal leptin concentrations and this change may facilitate or support the function of the HPO axis and accelerate resumption of ovarian cycling activity in primiparous, postpartum, suckled, anestrous cows.