Effect of breed and type of lambing on the concentrations of copper and zinc in blood, milk and wool from confined ewes fed a restricted diet.
15 days before lambing and 15, 30, 45 and 60 days after lambing, 23 Suffolk and 24 Rambouillet ewes in Mexico with twin or single lambs were weighed, and the concentrations of copper and zinc in blood, milk and wool samples were determined by spectrophotometry. Ewes were housed and were fed 1.5-2.5 kg oat straw (containing 13.5 p.p.m. copper and 66.5 p.p.m. zinc) and 1 kg concentrates (with 9 p.p.m. copper and 474 p.p.m. zinc) daily during the postpartum period. Body weight 15 days after lambing averaged 83.4 and 71.8 kg respectively for Suffolk and Rambouillet ewes (P<0.001), ewes with twin lambs weighed less than those with single-born lambs (74 vs. 81.1 kg), and there were significant stage of lactation × breed and stage of lactation × type of lambing interactions. Blood copper concentration was significantly affected by breed (0.65 and 0.42 p.p.m. for Suffolk and Rambouillet ewes respectively) and litter size (0.58 and 0.50 p.p.m. for ewes with single and twin lambs respectively). Breed had a significant effect on blood zinc concentration (5.45 and 6.2 p.p.m. for Suffolk and Rambouillet ewes respectively) and zinc content in wool (109.3 and 98.3 p.p.m.). Stage of lactation significantly affected the copper and zinc concentrations in blood, milk and wool. There were highly significant correlations of ewe body weight during lactation with blood copper and zinc concentrations (0.99 and 0.96 respectively).