Influence of dietary electrolyte balance and microbial phytase on growth performance, nutrient utilization, and excreta quality of broiler chickens.

The possible interaction between dietary electrolyte balance (DEB=Na+K-Cl, mEq/kg of diet) and microbial phytase on the performance and nutrient utilization of broiler starters and litter quality was examined in this study. A 4 x 2 factorial arrangement of treatments was used with 4 levels of DEB (150, 225, 300, and 375 mEq/kg of diet) and 2 levels of phytase (0 and 500 phytase units/kg of diet). Experimental diets were based on corn, soybean meal, and canola meal and were formulated to contain a nonphytate P level of 3 g/kg. The DEB levels were altered by the use of sodium bicarbonate and ammonium chloride. Each diet was offered to 6 replicates of 8 birds each from d 1 to 21. Increasing the DEB values from 150 to 300 mEq/kg had no effect (P>0.05) on the weight gains and feed per gain, but the gains were lowered (P<0.05) and the feed per gain was increased (P<0.05) at 375 mEq/kg. Feed intake was unaffected (P>0.05) by DEB levels. Supplemental phytase improved (P<0.05) the weight gains and feed intake at all DEB levels. Feed per gain was lowered (P<0.05) by phytase addition, but a tendency for a DEB x phytate interaction (P=0.06) was also observed, indicating that the responses to phytase may be affected by DEB level. The responses in feed per gain were greater at the lowest DEB level, and phytase addition had no effect on feed per gain at the highest DEB level. Dietary electrolyte balance levels had no effect on the AME(n) and ileal N digestibility to 300 mEq/kg, but lowered (P<0.05) both criteria at 375 mEq/kg. Phytase addition improved (P<0.05) the AME(n) and ileal N digestibility. The improvements in AME(n) with 500 U/kg of phytase addition in 150, 225, and 275 mEq/kg DEB were 53, 60, and 38 kcal/kg of DM, respectively. The main effect of DEB was significant (P<0.05) only for the ileal availability of Na and Cl, whereas added phytase influenced (P<0.05) the ileal availability of Ca, P, Na, K, and Cl. The effects of DEB were significant (P<0.05) for apparent ileal digestibility of all amino acids, except Ala (P=0.09), Arg, Met, and cystine. In general, the digestibilities of amino acids were unaffected when the DEB level was increased from 150 to 225 mEq/kg of diet, but decreased at the 300 and 375 mEq/kg levels. Phytase addition improved (P<0.06 to 0.05) ileal digestibility of all amino acids, except Met and Tyr. Increasing DEB had adverse effects on excreta scores and DM content. Phytase addition, however, had no effect on excreta quality. The overall results of the present study suggest that variability in phytase responses in nutrient utilization may be explained, in part, by differences in dietary electrolyte levels.