Effect of phytase supplementation on rumen fermentation characteristics and phosphorus balance in lactating dairy cows

This study aimed to evaluate the effects of exogenous phytase on rumen fermentation characteristics, the phosphorus (P)-flow at the duodenum and the P-balance in lactating dairy cows. For this purpose ruminal and duodenally fistulated cows were assigned to one of three dietary treatments: high P (HP) diet (n=7) provided a total of 45 g/d of P, archived by a supplementation of dicalcium phosphate to the diet; low P (LP) diet (n=5) provided 34 g/d of P without supplementation; LP+phytase (LP+PHY) diet (n=5) provided 34 g/d of P supplemented with an exogenous phytase. Dry matter intake and milk yield were recorded daily. In the first week of a sampling period Pbalance was determined. Samples of ruminal fluid were taken and duodenal chyme was collected in the second sampling week. Ruminal pH and the concentration of volatile fatty acids were not different between the treatments. The HP-group shows a higher P-flow at the duodenum than other groups. No differences in apparent total tract P-digestibility were found between the treatments. The P-balance in the HP-group (2.6 g/d) was higher compared to the LP (-3.2 g/d) and LP+PHY (-3.0 g/d) group. Overall, phytase supplementation had no effect on P-digestibility in lactating dairy cows.