Theses and Dissertations at Montana State University (MSU)
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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.Item The biostimulatory effect of bulls on postpartum follicular wave development in postpartum, anestrous, suckled beef cows(Montana State University - Bozeman, College of Agriculture, 2009) Wilkinson, Jarrod Robert Charles; Chairperson, Graduate Committee: James G. Berardinelli.The objective of this experiment was to determine if bull exposure influences follicular wave dynamics in primiparous, postpartum, anestrous, suckled, beef cows exposed to bulls. In Experiment 1, cows were exposed (continuously 24 h/d), (EB; n = 5) to bulls or not exposed to bulls (NE; n = 5) throughout the experimental period. In Experiment 2, cows were exposed to bulls for either 12 h, (EB12; n = 15), 6 h, (EB6; n =14) or not exposed to bulls (NE; n = 10) from the start to the end of the experimental period. In Experiments 1 and 2, cows were 67 d ± 3.8 (mean ± SE) and 51.5 ± 2.3 d postpartum at the start of the experiment. Follicular characteristics of each cow were examined by transrectal ultrasonography. In Experiment 1, interwave interval for wave 3 was shorter in EB than NE cows. Maximum dominant follicle (MDF) diameter tended to be greater during wave 2 for EB than NE cows, while wave 3 was greater for EB than NE cows. However, MDF diameter for wave 6 was greater for NE than EB cows. In Experiment 2, EB12 cows had fewer follicular waves to the resumption of luteal activity (RLA) than NE cows, while the number of waves to RLA for EB6 cows did not differ from that of EB12 or NE cows. Normalizing follicular waves to the time of RLA for cows within the EB12 and EB6 indicated that those cows at RLA had larger MDF diameters for the wave that produced the ovulatory follicle than cows that did not RLA. These data show the effects of bull exposure in altering follicular growth and developmental patterns, shortening the inter-wave interval and increasing the MDF diameter. Though the mechanism through which bull exposure alters postpartum follicular development is not entirely understood, these data provide new understanding.Item The biostimulatory effect of bulls on the hypothalamic-pituitary-adrenal and ovarian axes and on temporal aspects of resumption of ovarian cycling activity in primiparous, postpartum, anestrous, suckled, beef cows(Montana State University - Bozeman, College of Agriculture, 2008) Tauck, Shaun Austin; 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 the hypothalamic-pituitary-ovarian (HPO) and/or -adrenal (HPA) axes of cows. In Experiment 1, the hypothesis tested was that the biostimulatory effect of bulls is associated with adrenal regulation and/or function in anestrous cows. The biostimulatory effect of bulls was associated with mean concentrations of cortisol in postpartum cows. Experiment 2 was designed to determine if acute (5-h daily) bull exposure alters characteristics of patterns of cortisol and luteinizing hormone (LH) concentrations in postpartum, anestrous cows. Cows exposed acutely to bulls exhibited fewer pulses of cortisol and more frequent pulses of LH than cows exposed to steers. However, it was not known if these changes were related to resumption of ovarian cycling activity in postpartum, anestrous cows. Experiment 3 was designed to test the hypothesis that patterns of cortisol concentrations are altered by continuous, 24-h daily, bull exposure, before and after resumption of ovarian cycling activity in postpartum, anestrous cows. Continuous bull exposure decreased cortisol pulse frequency before cows resumed ovarian cycling activity. Experiment 4 tested the hypothesis that the overall shape of patterns of cortisol and/or LH concentrations may differ between cows exposed acutely to bulls or steers in Experiment 2. Cows exposed acutely to bulls had more uneven patterns of LH concentrations than cows exposed to steers and as patterns of cortisol concentrations became smoother, patterns of LH become more uneven in cows exposed acutely to bulls. In Experiment 5, the hypothesis tested was that interval to resumption of ovarian cycling activity may depend upon duration of daily bull exposure. Cows 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 activity of the HPA axis 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.