Effect of high dietary zinc concentration and length of zinc feeding on feed intake and tissue zinc concentration in sheep

Two experiments were conducted to study the effect of high dietary Zn concentration and length of Zn feeding on feed intake and tissue Zn concentration in sheep. In Experiment 1, 24 whethers were fed a basal diet containing 41 mg kg−1 Zn dry matter (DM) basis and supplemented with 0, 500, 1000, 1500, 2000, or 2500 mg kg−1 Zn as reagent grade ZnSO4 · 7H2O for 10 days and voluntary feed intake was measured daily. There was no difference in average feed intake among treatment groups. Intake of feed decreased between Day 2 and Day 5 for sheep given most diets, but recovered thereafter. In Experiment 2, 27 wethers were supplemented with 700, 1400, or 2100 mg kg−1 Zn added to the basal diet containing 30 mg kg−1 Zn (DM basis) for either 10, 20, or 30 days, in a 3 × 3 factorial arrangment of treatments. Three additional sheep were killed at the start of the experiment to serve as controls for tissue Zn concentration. Feed intake did not differ among treatments. There was no difference in bone, heart, or muscle Zn due to dietary treatment or time. Liver and kidney Zn increased with increasing dietary Zn and length of feeding period. Spleen Zn also increased with dietary Zn. The best fits to a linear model were found for liver and kidney Zn concentration at 20 days. These tissues appear to be the most sensitive for future Zn bioavailability studies with ruminants.