The effect of microbial phytase in a pearl millet-soybean meal diet on apparent digestibility and retention of nutrients, serum mineral concentration, and bone mineral density of nursery pigs.

Eighteen gilts (initial BW of 10.9 kg; age 4 wk) were used in a 35-d experiment to study the effects of adding microbial phytase to a pearl millet-soybean meal-based diet on growth, apparent digestibility and retention of nutrients, and bone mineral status. The dietary treatments were arranged in a 2 x 3 factorial with two levels of P (.58%, low-P or .95%, adequate-P) and three levels of microbial phytase (0, 700, or 1,000 units/kg of diet). Phosphorus, Ca, and N balance were determined from d 32 to 35. Blood samples were collected on d 0 and 35 for serum mineral analysis. Global bone mineral content (GBMC) and global bone mineral density (GBMD) were determined on d 0 and 35 using dual-energy x-ray absorptiometry (DXA). A microbial phytase level x P level interaction was observed for final BW, ADG, gain:feed (P < .001), and serum P concentration (P < .003). Phytase supplementation of the low-P diets increased final BW, ADG, gain: feed, and serum inorganic P concentration but did not improve growth or serum inorganic P concentration in pigs fed the adequate-P diets. The addition of microbial phytase to the low-P and adequate-P diets reduced fecal P (P < .01), fecal N (P < .05), increased P absorption and retention (P < .01), and increased N absorption (P < .05). Pigs fed the adequate-P diets absorbed more P (P < .01) but excreted more P (P < .01) in the feces. Phytase tended to increase Ca (P < .07) and N (P < .10) retention, apparent threonine digestibility (P < .06), and serum Zn concentration (P < .09). Phytase increased GBMC and GBMD (P < .04). Phosphorus also increased GBMC and GBMD (P < .007 and P < .002, respectively). These results show that supplemental microbial phytase in pearl millet-soybean meal diets increased P availability, decreased the amount of P excreted in feces, and increased bone mineralization in nursery pigs.