Reduced concentrations of limestone and monocalcium phosphate in diets without or with microbial phytase did not influence gastric pH, fecal score, or growth performance, but reduced bone ash and serum albumin in weanling pigs

An experiment was conducted to test the hypothesis that reducing limestone and monocalcium phosphate in diets for weanling pigs by lowering the concentration of Ca and P or by including microbial phytase in the diet will reduce stomach pH and fecal score and will improve growth performance of pigs. A total of 160 weanling pigs (5.75 ± 1.04 kg) were allotted to four corn-soybean meal-based diets in a completely randomized design with five pigs per pen. Diets for phase 1 (d 1 to 15) were formulated using a 2 × 2 factorial design with 2 concentrations of Ca and P (adequate or deficient levels of total Ca and digestible P) and 2 inclusion levels of phytase (0 or 2,000 units/kg feed). Phytase was assumed to release 0.16% total Ca and 0.11% digestible P. Common diets were fed in phases 2 (d 16 to 21) and 3 (d 22 to 35). Fecal scores were recorded in phase 1 and on d 15, gastric pH was measured and a blood sample and the right femur were collected from one pig per pen. Growth performance data were recorded within each phase. Results indicated that in phase 1, at deficient dietary Ca and P, pigs fed the diet with phytase had greater (P < 0.05) average daily gain (ADG) and gain to feed (G:F) compared with pigs fed the diet without phytase, but in diets with adequate levels of Ca and P, no effect of phytase inclusion was observed (interaction, P < 0.05). Without phytase, pigs fed the diet with deficient Ca and P had reduced (P < 0.05) G:F compared with pigs fed the diet with adequate Ca and P, but if phytase was included, there was no effect of Ca and P on G:F (interaction, P < 0.05). For phases 2 and 3, and from d 1 to 35, no differences among dietary treatments were observed for ADG or G:F. Bone ash was greater (P < 0.05) in pigs fed diets with adequate Ca and P than in pigs fed diets with deficient Ca and P, but no effect of phytase inclusion was observed on bone ash. Concentrations of Ca and P did not affect stomach pH or fecal score, but pigs fed diets with phytase tended (P < 0.10) to have reduced stomach pH and fecal score compared with pigs fed diets without phytase. Pigs fed diets with adequate Ca and P had greater (P < 0.05) albumin in serum than pigs fed the Ca- and P-deficient diets. In conclusion, phytase inclusion in phase 1 diets may reduce diarrhea, but lowering Ca and P does not reduce stomach pH or fecal score and decreases bone ash, although growth performance during the entire weanling period is not affected.