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 e xperiment to study the effects of adding microbial phytase to a pearl millet-soybean meal-based diet on growth, apparent digestibility and r etention 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 (CT, 700, o r 1,000 units/kg of diet). Phosphorus, Ca, and N balance were determin ed from d 32 to 35. Blood samples were collected on d 0 and 35 for ser um mineral analysis. Global bone mineral content (GBMC) and global bon e mineral density (GBMD) were determined on d 0 and 35 using dual-ener gy xray absorptiometry (DXA). A microbial phytase level x P level inte raction was observed for final BW, ADG, gain:feed (P < .001), and seru m P concentration (P < .003). Phytase supplementation of the low-P die ts increased final BW, ADG, gain: feed, and serum inorganic P concentr ation but did not improve growth or serum inorganic P concentration in pigs fed the adequate-P diets. The addition of microbial phytase to t he 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 di gestibility (P < .06), and serum Zn concentration (P < .09). Phytase i ncreased GBMC and GBMD (P < .04). Phosphorus also increased GBMC and G BMD (P < .007 and P < .002, respectively). These results show that sup plemental microbial phytase in pearl millet-soybean meal diets increas ed availability, decreased the amount of P excreted in feces, and incr eased bone mineralization in nursery pigs.