THE EFFECT OF GROWTH-RATE ON COPPER REQUIREMENTS OF GROWING LAMBS

An experiment was conducted to determine the effects and interactions of dietary energy and Cu on measures of nutritional Cu status in growi ng Lambs. The hypothesis was that dietary Cu requirements are affected by growth rate and caloric intake. In a 2 x 2 factorial design, 16 we anling lambs (ave. BW=22 kg) were assigned to dietary treatments of : 1) Low energy (LE), Low Cu; 2) LE, high. Cu; 3) high energy (HE), low Cu; and 4) NE, high Cu. The low and high Cu diets were formulated to c ontain 8 and 16 ppm; and the low and high energy diets were formulated to contain 2.1 and 2.5 McaL NE/kg, respectively. The diets were fed f or 16 wk and the lambs were slaughtered. Lambs fed the HE diets had hi gher average daily gain (ADG, 152 vs. 59 g/d, P<0.05) anal higher dry matter intake (DMI). Concentrations of Cu in liver were increased (P<0 .05) by high dietary Cu (390 vs 173 mu g/g, DM) but not affected by di etary energy. Concentrations of Cu in kidney and serum were not affect ed by dietary treatments. However, concentrations of Cu in bone were d ecreased and serum ceruloplasmin increased by high dietary energy. lit this trial, no effect of growth rate on the Cu requirement of lambs w as observed. The results indicate the Cu requirement of growing lambs is not affected by caloric intake and growth rate, but an interaction of dietary energy and Cu metabolism was shown for ceruloplasmin (Cp) a nd bone Cu.