Interpretive Summary: Effects of microbial phytase on standardized total tract digestibility of phosphorus in hybrid rye, barley, wheat, corn, and sorghum fed to growing pigs.
By: Anne Wallace
Hybrid rye is a high yield grain with a lower risk of ergot spoilage, used in various consumer food products but poorly studied as pig feed. In this study published in the July 2019 issue of Translational Animal Science, the digestibility of Phosphorus (P) in hybrid rye as compared to barley, wheat, corn, and sorghum was evaluated to characterize its usefulness in pig feed.
The authors hypothesized that for hybrid rye, apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P would be greater than in other cereal grains. They noted hybrid rye having high intrinsic phytase activity. Because P is bound to phytic acid in cereal grains, its digestibility is poor unless unbound. It was also hypothesized that STTD and ATTD would increase with microbial phytase, an enzyme that releases P from phytic acid.
A total of 112 barrows were evaluated in this study. Three varieties of hybrid rye and one of barley, wheat, corn, and sorghum were used as the primary P source of 7 different diets. Fourteen unique diets were comprised with the addition of seven identical diets with microbial phytase. Pigs were housed in metabolism crates for 14 days and fecal samples collected to analyze digestibility.
Diets with added microbial phytase had higher ATTD and STTD as expected. One hybrid rye variety had increased ATTD and STTD of P compared to wheat and sorghum. In the diets without microbial phytase, all hybrid rye varieties had greater STTD of P than sorghum and corn, one variety had greater STTD of P than wheat, and there was no difference from barley. The authors attributed this finding to the increased intrinsic phytase activity of hybrid rye.
To conclude, the addition of microbial phytase to hybrid rye, barley, wheat, corn, and sorghum feed increased the ATTD and STTD of P in this study. The STTP of P without microbial phytase was also found to be greater in hybrid rye compared to other grains. Therefore, supporting its known higher intrinsic phytase activity. Overall, hybrid rye may have usefulness in pigfeed due to its increased intrinsic phytase activity and total P when compared to some other cereal grains, such as sorghum and corn. More studies on the effects that heat, and intrinsic versus added phytase have on the digestibility of P in hybrid rye compared to other cereal grains may be warranted.
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