Rice is the third most widely grown cereal grain worldwide with over 700 million tons produced per year. Co-products from the processing of rice for human consumption are an abundant feed source for livestock. Research conducted at the University of Illinois is helping producers make the most of these ingredients.
Rice co-products include rice hulls, rice bran, broken rice and rice mill feed. Rice hulls primarily consist of lignin and ash and have no nutritional value. Rice bran is the outer part of the grain after the hulls have been removed. The bran is removed from brown rice to make polished white rice and makes up 8 to 10% of the weight of paddy rice. It can be fed as full fat rice bran or defatted rice bran.
Broken rice consists of kernels of polished rice that have been broken during the milling process. Rice mill feed is a combination of rice hulls, rice bran and rice polishings.
"Most of the phosphorus in rice co-products is hard for pigs to digest because it's bound to phytate," explains Hans H. Stein, a U of I professor of animal sciences. "About 84 to 88% of the phytate is in the bran layer so rice bran is a good source of phosphorus if we can get it into a form that pigs can absorb."
Microbial phytase, an enzyme produced by specially engineered microbes such as bacteria or yeast, breaks the bonds holding phosphorus to phytate. Microbial phytase has been used for years to improve phosphorus digestibility in U.S. swine diets based largely on corn and soybean meal. Stein, along with Ph. D. student Gloria Casas, set out to test its effects on the digestibility of phosphorus in rice co-products fed to pigs.
First, they fed a group of growing pigs diets containing rice co-products with no added phytase. The standardized total tract digestibility of phosphorus was greatest in broken rice at 75.6%. The digestibility of phosphorus in FFRB, rice mill feed, brown rice and DFRB ranged from 26.4 to 33.1%.
Adding phytase greatly improved phosphorus digestibility in some of the rice co-products. When phytase was added to the diets, the digestibility of phosphorus increased to 64.5% in brown rice, 41.3% in FFRB, and 46.7% in rice mill feed. The digestibility of phosphorus in broken rice and DFRB was not increased by the addition of phytase.
"Broken rice contains no bran so it has less phytate-bound phosphorus, but also much less phosphorus overall than co-products with bran," Stein says. "Using microbial phytase in combination with brown rice, rice mill feed or full fat rice bran makes these ingredients valuable sources of phosphorus in diets for growing pigs."
He adds that with the use of microbial phytase, producers can also decrease the amount of phosphorus excreted by pigs. "So this not only reduces the cost of adding supplemental phosphorus to the diets, but it also has benefits for the environment."
The paper, "Effects of microbial phytase on the apparent and standardized total tract digestibility of phosphorus in rice co-products fed to growing pigs" was published in a recent edition of the Journal of Animal Sciences. The full text is available online.