Effect of chromium supplementation and copper status on performance and reproduction of beef cows

Pregnant Angus (n = 83) and Simmental (n = 69) cows were blocked by age into three age blocks and then randomly assigned by breed within a block to one of two free choice mineral supplements to determine effects of dietary Cr and Cu status on performance and reproduction of beef cows. 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 days prepartum, at which time half of the cows in each treatment received a 25 g Cu oxide needle bolus. Blood was collected from 36 cows on days 0, 28, 58, 97 (approximately 20 days postpartum), 155, 210, and 279, and from 36 calves on days 196 and 279 for plasma Cu determination. Liver biopsies were taken on days 0 and 279 to determine initial and final liver Cu concentrations in cows. Plasma Cu concentrations were affected by Cu bolus × time (P < 0.05), breed × time (P < 0.01), and breed × bolus (P < 0.01) interactions in cows, and by a treatment × time interaction (P < 0.05) in calves. Liver Cu concentrations were affected by breed × time (P < 0.01) and Cu bolus × time (P < 0.05) in cows. Cows receiving a Cu bolus had higher (P < 0.05) plasma Cu on day 97, and higher (P < 0.05) liver Cu on day 279 relative to cows that did not receive a bolus. Simmental cows had lower (P < 0.01) plasma Cu at day 28 and at subsequent sampling days, and lower (P < 0.01) liver Cu on days 0 and 279 than Angus cows. Simmental cows that received a Cu bolus had higher (P < 0.01) plasma Cu concentrations than Simmentals that did not receive supplemental Cu. Supplemental Cr resulted in higher (P < 0.05) plasma Cu concentrations in calves on day 279 versus controls. Overall body weight loss and body weight loss postpartum in cows was affected by breed (P < 0.05) and treatment × block (P < 0.01). Overall and postpartum body weight loss was lower in Angus cows (P < 0.05). Chromium supplementation reduced (P < 0.01) overall and postpartum body weight loss in 2 and 3 years old cows, but not in older cows. Cows supplemented with Cr tended (P < 0.06) to have higher pregnancy rates than controls. Calf birth weights and weaning weights were not affected by Cr or Cu bolus. Results indicate that Cr supplementation may improve fertility and decrease postpartum body weight loss especially in young beef cows.