Master of Science (MS)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Twelve neonatal Holstein bull calves (38.52 ± 5.87 kg) were fed milk replacer at a fixed or varied meal time to determine the effects on metabolic hormone secretion, average daily intake, growth, and energy metabolism. Body weights were measured every two weeks from birth to 8 weeks. Rumen fluid was collected every two weeks from week 2 through 8. Serial blood collections were conducted every two weeks from week 2 through 8. Blood was collected, beginning at 0530, at 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 150 minutes. Plasma was analyzed for ghrelin, leptin, growth hormone (GH), and insulin-like growth factor-1 (IGF-1). Treatment did not affect body weight or average daily intake. Mean plasma ghrelin, leptin, GH, and IGF-1 concentrations were not affected by treatment. A treatment by week interaction was observed for plasma ghrelin concentrations. Plasma ghrelin concentrations were higher at weeks 2 and 4 in control calves. Plasma ghrelin concentrations decreased in all calves as they aged. A treatment by time interaction was observed for IGF-1, and a treatment by week by time interaction was observed for growth hormone and IGF-1. Growth hormone decreased as calves aged, while IGF-1 increased. There was no treatment effect or interactions of treatment and week on butyrate and propionate concentrations. However, both butyrate and propionate increased with age. Treatment and week effects were present for acetate, as well as a treatment by week interaction. Calves in the control group had a higher percentage of acetate. Acetate concentration increased in all calves as they aged. At weeks 4 and 8, intravenous glucose tolerance tests were performed to assess glucose clearance. A treatment effect was observed for glucose half life (T1/2), glucose clearance rate (k), and insulin. Glucose half- life was higher for calves in the control group, while the clearance rate was lower for the control group. Peak insulin concentrations were higher for calves in the treatment group. It is concluded that feeding time does not affect overall growth and feed intake, but does have an affect on the some of the regulatory mechanisms that control them.



Document Availability at the Time of Submission

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Committee Chair

Williams, Cathleen