Effects of particle size and phytase supplementation on apparent and standardized total tract digestibility of phosphorus in hybrid rye fed to growing pigs

Finely ground particle size and an increasing level of microbial phytase supplementation could improve phosphorus digestibility in hybrid rye fed to growing pigs. An experiment was conducted to investigate the effects of particle size (PS) and levels of phytase supplementation on the apparent (ATTD) and standardized (STTD) total tract digestibility of P in hybrid rye fed to growing pigs. Thirty-six growing barrows (23.6 +/- 1.5 kg initial BW) were individually housed in metabolism crates and randomly allotted to one of six dietary treatments to give six replicates per treatment. The six dietary treatments were arranged in a 2 x 3 factorial with main effects of PS and phytase supplementation levels (0, 500, or 2,500 FTU/kg). Hybrid rye was ground using a hammermill mounted with 4.0- and 3.2-mm screens to obtain material with coarse and fine PS, respectively. Pigs were fed experimental diets for 11 d, including 5 d for adaptation and 6 d for total collection of feces. All data were analyzed using the MIXED procedure of SAS with PS, phytase, and their interaction as fixed effects. Orthogonal polynomial contrasts were used to test linear and quadratic effects of phytase level in both coarse and fine hybrid rye diets. The ATTD and STTD of P were greater (P < 0.05) in diets with fine than in those with coarse hybrid rye. Increasing levels of phytase supplementation linearly (P < 0.01) and quadratically (P < 0.01) improved the ATTD and STTD of P in hybrid rye diets. There were no interaction effects between PS and phytase supplementation on the ATTD and STTD of P in hybrid rye diets. In conclusion, PS reduction improved the digestibility of P in hybrid rye, and supplementing increasing levels of phytase improved P digestibility in linear and quadratic manner in growing pigs fed hybrid rye diets. Lay Summary Cereal grains such as corn, wheat, and barley are widely used as an energy source in swine diets. However, due to their recent soaring prices, it is necessary to use alternative feedstuffs for swine. New commercial hybrid rye with improved ergot resistance and higher yield has been developed. This hybrid rye contains similar energy content as barley and sorghum, making it a promising ingredient for pigs. Phosphorus is an essential nutrient in swine diets for bone growth and cellular functions. However, most phosphorus in hybrid rye is bound to phytic acid, which is not digested well by pigs. The excessive phosphorus in swine manure may runoff and cause environmental problems such as eutrophication. Increasing phosphorus digestibility can decrease its excretion in pigs. Therefore, in the current study, we formulated six diets including fine or coarse hybrid rye particle size supplemented with three levels of phytase to determine the effects of particle size and phytase supplementation on phosphorus digestibility in hybrid rye. Our results showed that fine particle size and supplementing increasing levels of phytase could improve the phosphorus digestibility in growing pigs fed hybrid rye diets.