Effects of rearing regime, a chelating agent and the source of supplemental calcium and protein in the laying diet on egg shell thickness and performance of crossbred layers

Abstract

In a factorial experiment, crossbred pullets reared on a low plane of nutrition, based on a dietary regime of either all-mash or mash plus whole grain, were given laying diets, supplemented with ground limestone and cockle shell grit as alternative calcium supplements, and Australian soybean meal and meat and bone meal as alternative protein supplements, from 18 to 72 weeks of age. From 48 weeks of age the laying diets were fed with or without 600 p.p.m. EDTA. The effects of these treatments on shell quality, egg production, feed conversion and liveweight were examined. Pullets reared on the mash plus whole grain regime wereheavier at housing time, matured earlier, laid eggs with better shells and tended to perform more efficiently than the lighter pullets reared on an all-mash regime. Supplementation of the laying diet with cockle shell grit improved shell quality. This improvement was significant only for the first half of the laying cycle which occurred during the warmer part of the year. Calcium supplements had no effect on other traits studied. inclusion of Australian soybean meal in the laying diet resulted in better shell quality right through the laying year and rate of lay, egg weight and efficiency of feed conversion was significantly better than that of birds given diets based on meat and bone meal. The addition of 600 p.p.m. EDTA to the laying diet at 48 weeks of age had adverse effects on shell quality but egg production was not significantly affected.