Effects of Microbial Phytase Supplementation and Soaking of Barley-Soybean Meal on Availability of Plant Phosphorus for Growing Pigs

The efficacy of phytase supplement, 1200 U/kg, produced by Aspergillus niger on phytin phosphorus (P) availability was assayed in a 6 × 6 Latin square designed digestibility and balance trial with growing pigs at live weight 35–88 kg. The pigs were fed on barley-soybean meal diets without inorganic P either soaked for 3 h or without soaking. The P content of the control diet with added inorganic P was 6.5 g and that of unsupplemented diets 3.7 g/kg. The calcium content was 8.0 g/kg in all diets, and in the composition of other nutrients, the diets were equal. Soaking of the meal had no effect on digestibility of any nutrient. The digestibility of ash in a diet supplemented with phytase was improved (P<0.001). There were no differences in any organic constituent digestibility between the treatments. No effect on nitrogen utilization was found as a result of phytase addition or soaking. The addition of microbial phytase improved (P<0.001) the apparent absorption of P to 0.64 as compared to the unsupplemented 0.45. The retained P, on average 4.9 g/d in diets with supplementary phytase, was significantly higher (P<0.001) than that without, 3.7 g/d. In pigs fed a diet with additional inorganic P, the retention of P was 5.5 g/d. P retention in terms of daily amount of intake was greater (P<0.001) in diets with added phytase than without (0.58 vs. 0.44). From the diet with inorganic P supplementation a significantly lower value, 0.38 (P<0.001) was achieved than from the unsupplemented diets. Calcium digestibility and retention tended to be higher in phytase-treated diets. Owing to its effect on phytate P availability in a barley-soybean meal diet, phytase treatment of feedstuffs allows a greater proportion of the pig's P requirement to be met by P of plant origin and results in reduced losses of dietary P in faeces and urine.