Phytate phosphorus intake and disappearance in the gastrointestinal tract of high producing dairy cows.

Thirty Holstein cows were fed diets of 50% grain and 50% corn silage (dry matter basis) through the first 18 wk of lactation. Grain mixes were supplemented with inorganic calcium sources (aragonite, calcite flour, or albacar) to provide .6 or .9% dietary calcium (dry matter basis). Phytate phosphorus intake averaged 38.3 and 42.6 g/d in digestion trials conducted during wk 4 and 10 of lactation, respectively. Even though large quantities of feed and significant amounts of grain were consumed, 98% of dietary phytate phosphorus was hydrolyzed to inorganic phosphorus. Neither calcium source nor calcium quantity affected the hydrolysis of phytate phosphorus.