Effect of phytase level in a low phosphorus diet on performance and bone development in weaner pigs and the subsequent effect on finisher pig bone development

Abstract

Two experiments (Exp. 1 and Exp. 2) were conducted to investigate the effects of phytase inclusion levels in a low-P weaner pig (from 7.8 to 33 kg) diet and weaner pig nutrition on the finisher pig offered an adequate P diet from 33 to 100 kg. In Exp. 1, which was designed to examine growth performance and bone mineral status, 96 pigs [initial body weight (BW), 7.8 kg; 2 pigs/pen] were allocated to one of four dietary treatments: (T1) basal diet [2.2 g available P (aP)/kg]; (T2) basal diet and 500 phytase units (FTU)/kg; (T3) basal diet and 1000 FTU/kg; and (T4) basal diet and 1500 FTU/kg with 12 pens per treatment. Bones were collected from 12 randomly selected pigs per treatment (one pig/pen) at the end of the study (33 kg BW). The remaining 48 pigs were then offered a diet containing adequate Ca and P until slaughter (100 kg BW). There was a linear improvement in weaner pig feed conversion ratio (FCR; P < 0.01) as the level of phytase inclusion increased. There were linear increases in bone ash ( P < 0.01), bone Ca ( P < 0.01) and bone P ( P < 0.05) concentrations at 33 kg BW as the level of phytase inclusion increased. Offering weaner pig diets with increasing levels of phytase resulted in the finished pig (100 kg BW) showing quadratic ( P < 0.001) responses in bone ash, bone Ca and bone P concentrations with a maximum response obtained at 1000 FTU/kg. In Exp. 2, 16 entire male pigs (18.9 kg BW) were offered identical diets to those offered to the weaner pigs in Exp. 1 (n = 4) to determine coefficients of total tract apparent digestibility and P, Ca and N utilization. There was a linear increase in P ( P < 0.01) and Ca digestibility ( P < 0.05) as the level of phytase inclusion increased. Overall, increasing phytase supplementation in a low-P diet (2.2 g aP/kg) improved FCR and bone mineralization at the weaner stage (33 kg). In addition, phytase supplementation with 1000 FTU/kg in a weaner diet yielded maximum response in bone mineralization at 100 kg BW despite the fact that pigs were offered an adequate Ca and P diet from 33 to 100 kg BW.