Effect of supplementing microbial phytase in diets containing graded concentrations of calcium on performance, shell quality and bone mineral parameters in WL layers

An experiment was conducted to study the effect of supplemental phytase in diets containing graded concentrations of calcium (Ca) and non-phytin phosphorus (NPP) on performance of WL layers. Eight diets with four graded concentrations of Ca (35, 37.5, 40 and 42.5 g kg−1) and two concentrations of NPP (3 and 1 g kg−1) were prepared. The low phosphorus diets were supplemented with phytase (500 FYT kg−1). Each diet was fed ad libitum to 8 replicates consisting of 88 laying chickens each from 25 to 72 weeks of age. Data were compiled and analysed in 3 phases (phase 1, 25 to 40 weeks; phase 2, 41 to 56 weeks; phase 3, 56 to 72 weeks of age) and all the 3 phases as the overall period. The interaction between Ca concentration and phytase supplementation significantly influenced egg production (EP), feed intake (phase 1), egg weight (phase 3), egg mass (phase 2 and 3), feed efficiency (FE) and Ca and P concentrations in tibia ash at 44 weeks of age. Feed intake during phases 2 and 3, egg weight during phases 1 and 3, egg mass during phase 1, body weight during phases 1, 2 and overall period, egg shell defects, shell weight, shell percent and bone mineral parameters at 72 weeks of age were not affected by the interaction. EP, EM and FE improved significantly with increase in dietary Ca concentration from 35 to 37.5 g kg−1 in groups fed without phytase and further improvement was not observed at higher concentrations of Ca in diet. While the layer performance in groups fed 35 g Ca with phytase supplementation improved similar to those fed ≥37.5 g Ca kg−1 diet without phytase. The layer performance reduced significantly in groups fed diets supplemented with phytase at higher concentrations of Ca (40 and 42.5 g Ca kg−1) compared to those fed 35 g Ca kg−1 suggesting the inhibitory effect of higher dietary Ca concentrations on utilization of phytase phosphorus. Based on the study, it is concluded that WL layers reared in open sided poultry houses in tropical climate require lower intake of Ca (3.32, 3.80 and 4.00 g bird−1 day−1) when the diets are supplemented with phytase (500 FYT kg−1) compared to those fed without phytase (3.58, 4.14 and 4.30 g bird−1 day−1 during 25–40, 41–56 and 57–72 weeks of age, respectively, during phase 1–3). At higher concentrations of Ca (40 and 42.5 g kg−1), response to supplemental phytase appears to be reduced in terms of performance in layers.