DIETARY ZINC AFFECTS SERUM CONCENTRATIONS OF INSULIN AND INSULIN-LIKE GROWTH FACTOR-I IN GROWING LAMBS

Glucose tolerance and concentrations of insulin, somatotropin, insulin-like growth factor-I and cortisol were evaluated in lambs deficient, marginal or adequate in zinc. There were three treatments: 1) deficient (basal diet deficient in zinc; 3.7 mg zinc/kg diet); 2) marginal (basal diet + 5 mg zinc/kg diet); and 3) adequate (basal diet + 40 mg zinc/kg diet). Lambs fed the zinc-deficient diet had lower (P < 0.05) serum insulin concentrations 1 h after feeding compared with those fed the marginal diet, whereas the concentrations in lambs fed the adequate diet were intermediate. Dietary zinc did not affect plasma glucose or serum somatotropin before or after feeding or intravenous glucose administration. A growth hormone-releasing factor analog was given to evaluate concentrations of somatotropin. Serum somatotropin in response to growth hormone-releasing factor analog tended to be higher (P = 0.20) in deficient and marginal lambs when compared with adequate lambs. Serum insulin-like growth factor-I was lower (P < 0.05) in deficient lambs than in marginal or adequate lambs. Cortisol concentrations were not affected (P > 0.05) by zinc status. Severe zinc deficiency altered circulating concentrations of insulin, insulin-like growth factor-I and somatotropin, whereas a marginal deficiency had no effect in growing lambs.