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Effects of phytase on phosphorus digestibility of rice co-products fed to growing pigs
The objectives of this experiment were to determine the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P, and the effect of microbial phytase on ATTD and STTD of P in full fat rice bran (FFRB), defatted rice bran (DFRB), brown rice, broken rice, and rice mill feed when fed to pigs. Ninety six barrows (initial BW 19.4 ± 1.4 kg) were allotted to 12 diets with 8 replicate pigs per diet in a randomized complete block design. A basal diet based on corn and soybean meal was formulated and 5 diets were formulated by adding each of the 5 rice co-products to the basal diet. Six additional diets that were similar to the initial 6 diets with the exception that 500 units of microbial phytase (Optiphos; Enzyvia, Sheridan, IN) were included were also formulate. The ATTD of P was calculated for each diet using the direct procedure. The STTD of P was calculated for each diet by correcting the ATTD of P for the endogenous P losses. The ATTD and STTD of P in each rice co-product were calculated using the difference procedure. The concentration of P in feces was reduced (P < 0.05) from pigs fed diets containing microbial phytase compared with pigs fed diets without phytase. The total daily P output in feces from pigs fed diets with phytase was also less (P < 0.05) than in feces from pigs fed diets without microbial phytase, except for diets containing broken rice. Among the rice co-products, the greatest (P < 0.05) ATTD and STTD of P were observed for broken rice regardless of inclusion of phytase. The ATTD of P was greater (P < 0.05) for all ingredients except DFRB if microbial phytase was used than if no microbial phytase was used, and the STTD of P in brown rice, FFRB, rice mill feed was also greater (P< 0.05) if microbial phytase was used than if no microbial phytase was used. In conclusion, the STTD of P is greater in broken rice than in all other rice co-products. The STTD of P in brown rice, FFRB, DFRB, and rice mill feed is relatively low due to the high concentration of phytate in these ingredients, but addition of microbial phytase will increase the STTD of P in most rice co-products.
Keywords: phosphorus digestibility, pig, phytase