Composition of fibre in rice coproducts examined

Rice coproducts in pig diets add fat and fibre, but too much fibre can decrease energy absorption and digestibility. A recent study from the University of Illinois characterises the chemical composition of fibre in rice and its coproducts, which could lead to diet interventions for improved digestibility.

“Because of rice fibre’s low fermentability, there’s a high upside potential for increased digestibility if we can find specific enzymes that can help degrade those fibre. For pigs, the most important thing is to be able to get more energy out of each ingredient,” said Dr Hans Stein, Professor in the Department of Animal Sciences and the Division of Nutritional Sciences at the university, and co-author of the study published in Animal Feed Science and Technology.

A former doctoral researcher working with Dr Stein, Dr Gloria Casas, analysed the carbohydrate composition of several ingredients – brown, and broken rice, full-fat rice bran, defatted rice bran, and rice mill feed – in a laboratory in Denmark. She also evaluated the digestibility of each ingredient by simulating the environments of the pig stomach, small intestine, and large intestine, including fermentability by gut microbes.

The ingredients varied widely in starch, cellulose, lignin, and fibre content, among other specific carbohydrate fractions, but for all ingredients, the primary carbohydrates were arabinoxylans.

“Arabinoxylans are relatively complex fibers that consist primarily of two sugars, arabinose and xylose, though there are many others in there, too,” Dr Stein said. “That is true for all the rice coproducts, but the ratio between arabinose and xylose differs among the ingredients. That ratio, to some degree, influences the functionality of the fibers.”

Simulated (in vitro) digestibility was higher in brown and broken rice than for all other coproducts, which Dr Stein and Dr Casas expected, given that full-fat rice bran, defatted bran, and rice mill feed were much higher in insoluble fibres. The results confirm earlier digestibility studies the researchers completed with the same ingredients in pigs.

Dr Stein notes the results don’t just apply to pigs.

“Humans consume rice and rice bran all over the world. Knowing the specific fibre composition of these products will allow us to figure out which gut microbes are affected,” he said. “In humans, one of the major problems in terms of nutrition in our part of the world is that we don’t get enough fibre. If we consume these fibres, how will they affect our gut microbes?”