Several co-products from rice processing can be used as animal feed. Brown rice is the whole rice grain that is left after the hull layer has been removed, leaving the germ, starchy endosperm, and bran. Rice bran is the outer brown layer of brown rice, which is removed to produce white rice. It is high in fiber, and also contains about 15% crude protein and 14 to 20% fat. Rice bran can be fed as full fat rice bran or defatted rice bran. Broken rice, or brewer's rice, consists of white rice grains that have been damaged in processing. It is high in starch and contains little fat, fiber, or protein (Table 1).

Non–starch polysaccharides (NSPs), primarily arabinoxylan and cellulose, comprise 20 to 25% of defatted rice bran. NSPs reduce nutrient absorption and energy digestibility. Addition of exogenous xylanase to wheat co-products, which also have high concentration of NSPs, may improve digestibility of energy, but there is limited information about the effects of adding exogenous xylanases to rice co-products. Therefore, an experiment was conducted to determine the effect on concentrations of digestible energy (DE) and metabolizable energy (ME) of adding exogenous xylanase to diets containing full fat rice bran (FFRB), defatted rice bran (DFRB), brown rice, or broken rice.

Materials and methods

A total of 80 weanling barrows with an average initial body weight of 13.6 kg were fed one of ten diets. The basal diet was based on corn and soybean meal. Four experimental diets were formulated by including FFRB, DFRB, brown rice, or broken rice in the diets at 50%, while adjusting the corn and soybean meal so that the ratio remained constant. Corn, soybean meal, and rice co-products were the only sources of energy in the diets. Five additional diets that were identical to the initial five diets with the exception that they also contained 16,000 units of xylanase were also formulated.

Feces and urine were collected and analyzed to determine digestibility of gross energy and concentrations of DE and ME in the diets. The difference procedure was used to calculate energy digestibility in ingredients.

Adding xylanase increases DE and ME of rice bran

In the diets that did not contain xylanase, DE and ME were greatest (P < 0.05) in brown rice and in broken rice (Table 2). FFRB contained less DE and ME than broken rice on a dry matter basis, but DE and ME was not different from values in brown rice. DFRB contained less DE and ME than all other ingredients.

Adding xylanase to the diets did not result in an increase in DE or ME in brown rice or broken rice. However, addition of xylanase increased DE and ME in FFRB, resulting in DE and ME concentrations equal to or greater than in brown rice and broken rice. Adding xylanase increased the DE of DFRB on an as-fed basis, and the ME of DFRB on a dry matter basis, but DFRB still had the least DE and ME of all ingredients.

Key points

• Addition of microbial xylanase to diets containing full fat and defatted rice bran, which contain relatively high concentrations of NSPs, increased DE and ME. Addition of xylanase to diets containing brown rice or broken rice  did not increase DE and ME.
• Brown rice and broken rice had the greatest concentrations of DE and ME in the diets without added xylanase. When microbial xylanase was added to the diets, DE and ME in full fat rice bran were the same as or greater than in brown rice and broken rice.
• DFRB contained less DE and ME than brown rice and broken rice even if xylanase was included in the diets.

Table 1. Analyzed nutrient composition of brown rice, broken rice, full fat rice bran (FFRB) and defatted rice bran (DFRB)

Table 2. Concentration of DE and ME in brown rice, broken rice, full fat rice bran (FFRB), and defatted rice bran (DFRB) without or with xylanase

^a-eMeans within a column lacking a common superscript letter are different (P < 0.05).

This report is based on unpublished research by Gloria Casas and Hans H. Stein.