Exogenous Phytase Plus Cellulase and Phosphorus Excretion in Lactating Dairy Cows

The objectives were to assess the effects of exogenous phytase plus cellulase on P excretion in lactating cows. The effects of an exogenous phytase plus cellulase mixture and dietary P content on P partitioning and excretion were evaluated in nine early lactation cows (mean = 27 d in milk); six of the cows were ruminally cannulated. Cows were assigned to treatments in replicated (three) 3 × 3 Latin squares, and each cow received each treatment sequentially in three, 21-d periods. Diets were 45% forage (all corn silage) and included supplemental P (high P; 0.47%), no supplemental P (low P; 0.32%), or no supplemental P with exogenous phytase (low P-enzyme; 0.32%). Total collection of milk, urine, and feces was conducted on d 19 to 21 of each period. There were no effects of dietary P or exogenous phytase plus cellulase on DMI, milk yield, or milk composition. Excretion of feces was unaffected by diet, but urine excretion was less by cows fed the low P diets than by cows fed the high P diets (16.5 vs 21.3 kg/d). Compared with cows fed high P diets, cows fed the low P diets had reduced P intake (68.1 vs 103.9 g/d), reduced fecal (34.4 vs 51.3 g/d) and urinary P excretion (2.8 vs 9.2 g/d), and lesser P balance (-8.0 vs. 4.4 g/d). The addition of exogenous phytase plus cellulase did not affect P intake, milk P, fecal P, or urinary P excretion, but apparent P digestibility tended to be greater in cows fed diets supplemented with the enzyme formulations (50.1% vs 40.5% for low P-enzyme and low P, respectively).