Disappearance of Phosphorus in Phytate from Concentrates In Vitro and from Rations Fed to Lactating Dairy Cows

Abstract

Objectives were to determine concentrations of P in phytate in selected concentrates, disappearance of P in phytate from these concentrates in vitro, and extent of hydrolysis of phytate in vivo. Total P and P in phytate were determined for eight concentrates; 32 to 81% of total P was in phytate. Six concentrates were incubated in vitro to determine the extent of phytate disappearance from solids and its appearance and disappearance from solution. Greater than 90% of P in phytate disappeared from solids between 6 and 8h of incubation in vitro (wheat middlings, rice bran, hominy, soybean meal, and dried distillers grains) or between 12 and 24h (cottonseed meal). Phosphorus in phytate in solution was hydrolyzed by 12h except for cottonseed meal (by 24h). Hydrolysis of the inositol ring to release P in vivo was greater than 99%, based on total fecal collection from 11 cows and the use of Cr as an indigestible marker in excreta, and between 94 to 98% for the same samples when acid detergent lignin was used as an indigestible marker to calculate phytate disappearance. These results further indicate that P in phytate should be considered available to lactating dairy cows when rations to meet their P requirements are being formulated.