Phosphorus Utilization and Characterization of Excreta From Swine Fed Diets Containing A Variety of Cereal Grains Balanced For Total Phosphorus

Intrinsic phytase in swine feeds may alter phytate utilization and solubility of excreted phosphorus. Therefore, the objective of this experiment was to quantify changes in fecal phosphorus composition from swine fed various cereal grains with a range of phytate concentrations and endogenous phytase activities. Twenty-five crossbred barrows weighing 89.3 + or - 6.8 kg were fed one of five diets based on corn, barley, low phytate barley, high fat-low lignin oat or wheat. Experimental diets were formulated to contain 75% of the test grain and were fed for a seven-day acclimation period followed by a three-day fecal collection. Total tract apparent digestibility coefficients were determined for dry matter, phosphorus and phytate using the indicator method. Fecal phosphorus was characterized using solution state phosphorus nuclear magnetic resonance spectroscopy (31P-NMR). Water soluble phosphorus (WSP) and the ratio of WSP to total phosphorus (WSP:TP) were determined in the feces. Apparent digestibility coefficients for phosphorus and phytate ranged from 0.33 (barley) to 0.45 (low phytate barley) and 0.32 (corn) to 0.79 (oat), respectively. The majority of phosphorus excreted in the feces was in the form of phosphate (> 48% of total phosphorus), and phytate degradation was not related to the endogenous phytase activity in the feeds. There was a positive linear relationship between dietary neutral detergent fiber and apparent total tract phytate digestibility, indicating that higher dietary fiber levels may enhance microbial breakdown of phytate in the hind gut. There was a negative relationship between the fecal WSP:TP and the % of total phosphorus in the form of phytate in the feces. In summary, our results indicate that the majority of the phosphorus in the feces of pigs fed cereal grains is present in the form of phosphate and only small amounts of phytate are contained in the excreta. The exception to this was the corn diet where 45% of the total fecal P was in the form of phytate. This hydrolysis of phytate in the gut did not appear to be related to the content of either phytate or phytase in the grain but was related to dietary fiber concentrations