An experiment was conducted to determine if glucose infusion could alter hypothalamic, pituitary or ovarian function in the postpartum (PP) beef cow. Twenty-six cows were assigned randomly at parturition to one of three infusion treatments. Controls (CON, n = 8) received 0.9% NaCl from days 26 to 32 PP. Glucose-infused animals (GLU, n = 8) received glucose at a constant rate of 4 mg min−1 kg−0.75 from days 26 to 32 PP, while glucose-spiked cows (SPIKE, n = 10) received glucose at rates up to 8 mg min−1 kg−0.75 for 48 h (days 26 and 27 PP), then received 0.9% NaCl as in CON. On day 32 PP 25 μg of gonadotrophin-releasing hormone (GnRH) was injected intravenously and blood samples were taken at 15- to 30-min intervals to evaluate pituitary release of luteinizing hormone (LH). During the entire infusion period, GLU had lower (P < 0.05) daily free fatty acid concentrations than either SPIKE or CON. Plasma concentrations of glucose in cows receiving the SPIKE treatment were elevated (P < 0.05) during the 48-h infusion period when compared to GLU and CON. In addition, glucose concentrations were higher (P < 0.05) in the GLU group than in the CON group during the first 48 h of infusion. For the remaining 4 d of the infusion period, plasma concentrations of glucose were similar between CON and GLU. Plasma insulin values were numerically but not significantly higher in GLU than in CON over the 6-d infusion period. During the 48-h glucose spike treatment insulin levels were elevated (P < 0.05) over preinfusion values and higher (P < 0.05) than both CON and GLU. Glucose infusion did not alter concentrations of plasma LH or the response to exogenous GnRH. The number of cows exhibiting ovarian activity by day 53 PP was similar among treatments. Key words: Beef cattle, glucose, reproduction, energy, luteinizing hormone, metabolism
Effects of Supplementing Excess Amounts of Metabolizable Protein from a Moderately Abundant Rumen Undegradable Source on Ovarian Function of Beef Cows Consuming Low Quality Forage
