Zinc Requirement of the Growing Lamb Fed a Purified Diet

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Abstract
The objective of this experiment was to quantitate the zinc requirement of growing lambs fed a purified diet. Twenty-four lambs averaging 14.8 kg were allotted to 4 treatment groups. The groups were assigned to 1) basal; 2) basal + 15 mg Zn/kg; 3) basal + 30 mg Zn/kg; and 4) basal + 45 mg Zn/kg of diet. The basal diet, which contained 3 mg Zn/kg and 0.72% Ca, was a purified diet based on egg white protein. The experiment was conducted for 11 weeks. By the end of the third week, deficiency symptoms were noted in the animals receiving the basal diet. The deficiency symptoms included reduced gains, feed consumption and feed efficiency, listlessness, loose wool, depraved appetite (especially for wool), scabby lesions and general dermatitis. At the end of 11 weeks, the average daily gain, feed consumption and feed per kilogram of gain were, respectively, in kilograms: 1) 0.11, 0.76, 7.00; 2) 0.23, 1.04, 4.51; 3) 0.25, 1.17, 4.57; and 4) 0.25, 1.11, 4.39. A significant (P < 0.01) quadratic regression due to zinc level was found among treatment means for gains, feed per kilogram of gain, serum proteins and serum Zn levels. Blood carbonic anhydrase increased linearly with increasing levels of dietary Zn (P < 0.01). Blood glucose and rumen fluid pH and volatile fatty acids were not significantly affected by treatments. Eighteen parts per million of Zn appeared to correct histological changes and low tissue Zn induced by the 3-ppm Zn diet but did not support maximal growth.