Digestible phosphorus requirements and efficacy of phytase for terminal-cross barrows and gilts fed sorghum-soybean meal based diets

Abstract

Experiment 1 evaluated sorghum-soybean meal diets containing the NRC (1988) levels of available P (.52,.47,.41% total P from 25 to 50, 50 to 80, and 80 to 118 kg, respectively) and diets containing either 125% (.58,.52, .44% total P) or 75% (.47,.43,.35% total P) of NRC levels for available P. Up to 80 kg, performance was not affected by dietary treatment and P excretions decreased with decreasing dietary P. From 80 to 118 kg, the 75% NRC diet reduced pig performance and increased P excretions due to reduced feed efficiency and low digestibility of P in the all plant P diet. Structural soundness in the live pig, carcass measurements, quality scores of the loineye, and sensory scores of loin chops were not adversely affected by treatment. Decreasing dietary P reduced the amount of connective tissue in the lean as determined by taste panel scores. Experiment 2 evaluated the 100% of NRC diets used in Exp. 1 and the same diets without inorganic P and either 0, 300, or 500 FTU/kg of phytase (NatuphoSTM, BASF Corp.). Pigs were fed from 50 to 118 kg. Removing the inorganic P decreased ADG and lowered bone ash and peak load of metacarpals and metatarsals. Supplementing phytase restored performance and bone traits to levels equal to or exceeding the P supplemented diet. The 300 FTU/kg treatment was almost as effective as the 500 FTU/kg treatment. Quantitative carcass traits, quality scores of the loineye, chemical analyses of the lean, and sensory scores for flavor and tenderness of loin chops were not affected by treatment. Phytase improved digestibility of Ca and P at both the ileum and over the total tract. In Exp. 1, the greatest reductions in P excretions occurred from feeding the 75% NRC treatment to 80 kg and the 100% NRC treatment after 80 kg. Compared to the 125% NRC treatment, P excretions were reduced 18%. Supplementing phytase in Exp. 2 reduced P excretions 61 %. Phytase was more effective at reducing P excretions than lowering dietary P levels.