Effects of time of commencement and duration of protein restriction on egg-type pullets reared in summer and winter

Abstract

A diet containing 10 per cent protein and 11.31 MJ M.E. kg-1 was fed to six groups of eggtype pullets from either day old or four weeks for 8, 12 and 16 weeks in both summer and winter. The same diet was also fed to another group from 8 to 20 weeks of age in both seasons. During the rest of the rearing period of each treatment a diet containing 16 per cent protein was fed to 20 weeks of age. The control group was fed a diet containing 20,16 and 12 per cent protein and 12.1 5 MJ M.E. kg-1 from day old, 6 and 14 weeks of age respectively. In both seasons, feeding the restrictive diet resulted in a reduction in the cost of feeding and in body weight gain to 20 weeks of age; and a delay in maturity compared with the control without adversely affecting egg production traits or increasing food consumption during the laying phase. Pullets fed the restrictive diet from day old ate less food during rearing, matured later and tended to lay smaller eggs throughout the laying period than their counterparts which were restricted from four to eight weeks of age in both experiments. Food consumption was not affected by the duration of restriction in either rearing season. However, feeding costs and body weight of pullets at the end of both rearing seasons were reduced progressively by increasing the duration of restriction. Rate of mortality was not affected by the rearing treatments when the birds were reared in summer, whereas in winter pullets restricted from day old for 12 to 16 weeks had the higher rate of mortality. Mortality during laying was not affected by the rearing treatments in either season. The results of both experiments suggest that for maximum return the optimum age for feeding the low protein diet is from 4 to 20 weeks of age in either season.