The influence of calcium and phosphorus in prelayer diets and their interaction with sodium chloride and potassium sulfate in layer diets on egg production and shell quality in crossbred layers

Abstract

In a 43x2 factorial experiment, 576 White Leghorn x Australorp pullets attaining 50% egg production at about 180 days of age were given from 22 to 26 weeks of age pre-layer diets with 10.4 or 25.8 g kg-1 calcium and 6.2 or 10.9 g kg-1 phosphorus. From 26 to 74 weeks of age these pullets were given layer diets with three levels (0, 1.5 and 7.0 g kg-1) of added sodium chloride and two levels (0 and 6.0 g kg-1) of added potassium sulfate. The calcium content of the pre-layer diet had no significant effect on feed intake, bodyweight gain or tibia-ash content between 22 and 26 weeks of age, or on egg production, egg weight, feed conversion efficiency and mortality in the subsequent laying phase. The higher level (25.8 g kg-1) of calcium improved (P<0.05) the shell quality of the first eggs laid and prevented a decline in shell quality due to excess sodium chloride (7.0 g kg-1) in the layer diet. A phosphorus level of 10.9 g kg-1 of the pre-layer diet reduced (P<0.05) feed intake, and in the subsequent laying phase both hen-housed egg production and efficiency of feed conversion were reduced (P<0.05). The adverse effect on feed conversion efficiency was alleviated by adding potassium sulfate to the diet. The level of phosphorus in the pre-layer diet had no significant effect on tibia-ash content or egg shell quality. The dietary level of sodium chloride had no significant effect on egg weight, feed intake and bodyweight gain. The inclusion of sodium chloride at a level of 7.0 g kg-1 diet tended to depress rate of lay by 2.0% and during the first half of the laying cycle, increased mortality by 12.5% (P<0.05) and reduced egg shell weight and thickness (P<0.05) in birds given pre-layer diets with a low calcium content. A daily intake of 137 to 139 mg of sodium per bird was not adequate for maintenance of egg production and efficiency of feed conversion in crossbred layers. The sodium requirement of a crossbred layer given a diet containing meat and bone meal is about 160 mg/day. The adverse effects due to either a low intake of sodium or a high level of sodium chloride in the diet were alleviated by the inclusion of 6.0 g kg-1 potassium sulfate in the diet. The inclusion of potassium sulfate (6.0 g kg-1) in the layer diet increased rate of lay by 2.1% (P<0.05).