Effect of a novel bacterial 6-phytase on nutrient digestibility in lactating dairy cows.

Abstract

Undigested P and N are excreted and contribute to the environmental impacts of dairy farming. Degradation of phytate in the rumen has been shown to be high but variable, leading to incomplete phytate-P utilization and resultant antinutritional impacts of phytate along the gastrointestinal tract. We investigated the effect of a novel bacterial 6-phytase (PhyG) on the apparent total-tract digestibility (ATTD) and excretion of DM, phytate-P (PP), P, CP and NDF in lactating dairy cows. Forty-eight lactating Holstein-Friesian cows were assigned to 3 treatments with 16 cows per treatment in a randomized block design. Cows averaged 44.1 kg milk/d, and 124 DIM at the experiment start. Diets were fed ad libitum as a TMR that was formulated to meet nutritional requirements except for P which was fed at 92% of the recommendation. Treatments comprised a control diet (CON) and the control diet supplemented with 2,000 or 5,000 phytase units/kg DM of PhyG. The experiment lasted for 19 d including a 14 d diet adaptation period and a 5 d fecal collection period. Dry matter intake did not differ across treatments. The ATTD of PP in CON was 88.5%, indicating incomplete phytate degradation. The ATTD of ash, P and CP increased linearly, whereas the ATTD of PP and NDF increased both linearly and quadratically with increasing PhyG dose level; with PhyG at 5,000 FTU/kg, the ATTD of PP, P, CP and NDF increased by 9.2, 13.7, 4.1 and 7.5% points above CON, respectively. Fecal excretion of ash, PP, P and NDF were reduced linearly. Supplementation of PhyG also reduced excretion of PP quadratically and CP excretion tended to be reduced linearly. Body weight and milk yield did not differ across treatments, but milk protein yield tended to increase linearly with increasing PhyG dose. The addition of PhyG to the diet of lactating dairy cows improved nutrient utilization and decreased nutrient excretion. It could therefore contribute to reducing the environmental impacts of dairy production.