THE USE OF DIETS CONTAINING HIGH-LEVELS OF ZINC FOR CONTROLLING EARLYGROWTH IN FEMALE BROILER CHICKS

A study was carried out with White Rock female chicks to evaluate the possibility of using dietary Zn supplied as ZnO, to control feed intak e and weight gain during the period of 1 to 3 wk of age. The levels of supplemental Zn tested were 0, 0.25, 0.50, and 1.0% (Experiment 1); 0 , 0.65, 0.75, and 0.85% (Experiment 2); 0.7 and 0.8% (Experiment 3). T he effect of Zn supplementation was compared with that of a low sodium chloride diet (L-NaCl-D) and of severe feed restriction (SFR), which was calculated to supply energy only for maintenance (Experiments 1 an d 3, respectively). The compensatory growth of the chicks from 3 to 4 wk of age was also evaluated. Feed intake and weight gain were negativ ely proportional to the levels of dietary Zn supplementation and there were significant (P < 0.02 and P < 0.01, in Experiments 1 and 2, resp ectively) negative correlations between supplemental dietary Zn levels and relative weight gains (values observed in the unsupplemented diet = 100%). The effects of L-NaCl-D and SFR on decreasing weight gain we re calculated, according to the equations obtained in Experiments 1 an d 2 to be equivalent to these of 0.58 to 0.65% and 0.78 to 0.87% Zn su pplementation, respectively. Relative weight gain and feed efficiency of the chicks from 3 to 4 wk of age, after withdrawal of the growth-de pressing factors, were positively related to the degree of growth depr ession during 1 to 3 wk of age; however, the intensity of recovery fro m a similar degree of growth depression induced by L-NaCl-D, SFR, or d ietary Zn was least in the last mentioned treatment. It is concluded t hat dietary Zn supplementation can be used as an efficient tool for co ntrolling early growth of young broiler breeder chicks.