Effect of phytase superdosing, myo-inositol and available phosphorus concentrations on performance and bone mineralisation in broilers

A total of 2,376 one-day-old Ross broiler chickens were used to investigate the effect of myo-inositol (MYO) and phytase supplementation on performance and bone mineralization variables in broilers fed diets formulated to have varying concentrations of available phosphorus (P). The trial was designed as a 2 × 2 × 3 factorial; with and without phytase superdosing (0 or 1,500 FTU/kg), MYO (0 or 3 g/kg), and dietary P (low, moderate or high). At 21 d, dietary phytase and MYO had no consistent benefit on bone mineralization variables. Bone ash reduced by 4.7% from the medium to low P diet (P < 0.01), with no effect of phytase supplementation. Superdosing improved bone P content by 6% in birds fed the low P diet, signifying an interaction between dietary P concentrations and phytase (P < 0.05). Dietary MYO addition resulted in a numerical reduction in bone ash and a significant reduction in bone strength (P < 0.05). At 42 d, the beneficial effect of phytase superdosing on feed intake and body weight gain was evident in the low P diet. Superdosing reduced feed conversion rate (FCR) at all P levels (P < 0.05), although this effect was more pronounced on the low P diet, suggesting that sufficient P being released from the phytase itself to re-phosphorylate MYO and hence improve FCR. The significant improvement in FCR was greater with superdosing than with MYO alone, and the combination led to no further improvement in FCR compared with superdosing alone, signifying a phytase and MYO interaction (P < 0.05). From these results, it can be estimated that MYO is providing around 30% to 35% of the total response to superdosing.