calcium, nursery pigs, phosphorus, phytase


A total of 720 nursery pigs (PIC 1050 × 280, initially 13.4 ± 0.47 lb) were used in a 42-d growth study to determine the effects of feeding 2 calcium (Ca) and 3 standardized total tract digestible (STTD) phosphorus (P) concentrations on growth performance and bone ash content. Pens of pigs (10 pigs/pen, 12 pens/treatment) were blocked by initial pen weight, and within blocks pens were allotted randomly to 1 of 6 dietary treatments. Dietary treatments were arranged in a 2 × 3 factorial, with 2 levels of Ca (0.58 vs. 1.03%) and 3 levels of STTD P (0.33 and 0.45% without phytase, and 0.45% with 0.12% of the P being released by phytase). Diets were provided in 3 phases, with pigs fed experimental diets during phase 1 (d 0 to 14) and phase 2 (d 14 to 28), followed by a common phase 3 diet from d 28 to 42. For the majority of the feeding periods, Ca × P interactions were observed for growth responses (P<0.05). From d 0 to 28, when diets contained low Ca concentration, pigs fed 0.45% STTD P with phytase had greater (P<0.01) ADG and ADFI compared with those fed 0.45% STTD P without phytase or 0.33% STTD P. When high Ca was fed, ADG and ADFI were similar among pigs fed 0.45% STTD P with or without phytase but were greater than those fed 0.33% STTD P. Feed efficiency was poorer (P<0.01) when low STTD P and high Ca were added to diet compared with other dietary treatments. During phase 3, pigs previously fed 0.33% STTD P had similar ADG, but decreased (P<0.05) ADFI and improved F/G compared with pigs previously fed 0.45% STTD P with or without phytase. However, pigs fed 0.33% STTD P, with high Ca were not able to fully compensate for the negative effects of P deficiency, resulting in decreased (P<0.05) overall ADG and ADFI compared with pigs fed 0.45% STTD P diet with or without phytase. On d 21, 1 median-weight gilt from each pen was euthanized and fibulas were collected for analysis of bone ash content. Pigs fed 0.33% STTD P had decreased (P<0.05) bone ash concentration compared with those fed 0.45% STTD P with or without phytase when high Ca was added to diets, but this P effect was not observed when diets contained low Ca concentration (Ca × P interaction, P = 0.007). In conclusion, excess Ca in diets decreased growth performance and bone ash concentration of nursery pigs when diets were deficient in STTD P. Adding phytase to achieve 0.45% STTD P in diets improved ADG and ADFI of pigs compared with diets containing 0.45% STTD P without phytase, indicating a potential underestimation of the P release from phytase or an increased availability of other nutrients liberated by phytase.


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