The use of diets containing high levels of zinc for controlling early growth 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 intake 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). The 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 and 3, respectively). The compensatory growth of the chicks from 3 to 4 wk of age was also evaluated. Feed intake and weight gain were negatively proportional to the levels of dietary Zn supplementation and there were significant (P < 0.02 and P < 0.01, in Experiments 1 and 2, respectively) 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 were calculated, according to the equations obtained in Experiments 1 and 2 to be equivalent to these of 0.58 to 0.65% and 0.78 to 0.87% Zn supplementation, respectively. Relative weight gain and feed efficiency of the chicks from 3 to 4 wk of age, after withdrawal of the growth-depressing factors, were positively related to the degree of growth depression during 1 to 3 wk of age; however, the intensity of recovery from a similar degree of growth depression induced by L-NaCl-D, SFR, or dietary Zn was least in the last mentioned treatment. It is concluded that dietary Zn supplementation can be used as an efficient tool for controlling early growth of young broiler breeder chicks.