Browsing by Author "Scott C. Whisnant, Committee Member"

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    The Effect of Supplemental Chromium and Copper Status on Glucose Metabolism, Performance, and Reproduction of Beef Cattle.
    (2005-03-01) Stahlhut, Heather Suzanne; Scott C. Whisnant, Committee Member; Jerry W. Spears, Committee Chair; Matt H. Poore, Committee Member
    A trial was conducted to determine the effect of supplemental chromium and copper status on glucose metabolism, performance, and reproduction of beef cattle. Pregnant Angus (n=83) and Simmental (n=69) cows were blocked by age and breed and randomly assigned to one of two free-choice mineral supplements. Supplements consisted of: 1) control (no supplemental Cr) and 2) 40 mg Cr /kg of mineral (from Cr picolinate). Mineral supplements were formulated to contain all minerals typically supplemented to cattle diets with the exception of Cu. The study began approximately 75 d prepartum, at which point half of the cows in each treatment received a 25 g Cu oxide needle bolus. Over the course the study, cows supplemented with chromium had lower plasma glucose and nonesterified fatty acid concentrations than control cows. Angus had higher plasma glucose concentrations than Simmental cows for the duration of the study. Glucose challenges were conducted pre- and postpartum to determine the effect of chromium supplementation on glucose metabolism in late gestation and early lactation in beef cows. Following a glucose challenge prepartum, plasma glucose and serum insulin concentrations were lower in animals receiving supplemental chromium. In cows receiving a copper bolus, chromium supplementation resulted in higher plasma glucose concentrations following a glucose challenge postpartum; however, no difference in plasma glucose concentrations was observed between treatments in animals that did not receive a copper bolus. Serum insulin was lower at 10 and 20 minutes following glucose infusion in the postpartum challenge in cows receiving supplemental chromium. Area under the curve and glucose clearance rates were not affected by treatment in either the pre- or postpartum glucose challenges. Breed differences were observed in basal plasma glucose as well as plasma glucose, NEFA, and serum insulin following the glucose challenges. Angus had higher plasma glucose concentrations following the postpartum glucose challenge. Serum insulin was higher and plasma NEFA concentrations were lower in Angus cows following glucose infusion during prepartum and postpartum glucose challenges when compared to Simmental cows. Cows receiving supplemental chromium lost less weight throughout the course of the study than control animals, and tended to have higher pregnancy rates than control cows. Over the course of the study as well as the period postpartum, young cows (2 or 3 years of age) receiving supplemental chromium lost less weight than controls. Control cows in replicates 2 (4 and 5 years of age) and 3 had higher plasma NEFA concentrations when compared to cows receiving chromium in the same replicates; indicating greater mobilization of fat stores. Simmental cows lost more weight than Angus over the course of the study and during the postpartum period. Chromium supplementation lowered plasma NEFA concentrations in cows that did not receive a copper bolus, and tended to lower NEFA concentrations in cows supplemented with copper. Chromium supplementation did not affect calf performance, morbidity, and mortality. Simmental calves, male calves, and calves born to older cows (replicates 1 and 2) had higher birth and weaning weights than Angus calves, heifer calves, or calves born to young cows. In conclusion, chromium and copper status altered glucose metabolism in reproducing beef cows. Supplemental chromium decreased the amount of weight lost by cows postpartum, and may increase pregnancy rates in beef cows.