Influence of high calcium rearing diets, Christmas Island phosphate and ethylenediamine-tetraacetic acid on the laying performance of White Leghorn × Australorp hens

Abstract

White Leghorn x Australorp pullets were reared on diets with either low (0.91-1.12 per cent) or high (1.45-1.93 per cent) levels of calcium; in the laying phase pullets from each rearing regime were fed diets with either sterilized bone meal or Christmas Island phosphate as sources of supplemental phosphorus. Each of these layer diets was supplemented with 0, 300 or 500 p.p.m. of EDTA. The level of calcium in the rearing diets had no significant effect on liveweight, feed intake or mortality of the pullets during either the rearing or laying phases. High calcium starter and grower diets, however, reduced rate of lay by 2.1 per cent (P < 0.05) and efficiency of feed conversion by 3.7 per cent (P < 0.01). There was also a non-significant tendency to lower shell thickness. The inclusion of 2.5 per cent Christmas Island phosphate in the laying diet, resulting in a daily intake of 46 mg of fluorine per hen, decreased rate of lay by 2.2 per cent (P < 0.05), hen-housed egg production by 11 eggs (P < 0.05) and efficiency of feed conversion by 5.0 per cent (P < 0.01). The addition of 300 p.p.m. EDTA to the laying diet significantly (P < 0.01) improved efficiency of feed conversion by 4.7 per cent. Neither the source of phosphorus nor the dietary level of EDTA had any significant effects on liveweight, egg weight, feed intake, shell quality or mortality.