Rice bran is the brown outer layer of brown rice, which is removed from brown rice to produce white polished rice for human consumption. Rice bran may be full fat, containing 14 to 25% fat, or defatted, which reduces the concentration of fat to less than 5%.

Rice bran has a high concentration of non-starch polysaccharides (NSP), primarily arabinoxylan and cellulose. NSPs decrease nutrient digestibility and thus limit the inclusion of rice bran in weanling pig diets. Recent data from our laboratory indicate that adding exogenous xylanase to diets containing full fat rice bran (FFRB) or defatted rice bran (DFRB) increases the concentrations of digestible and metabolizable energy. The objective of this experiment was to determine the effects of increased inclusion levels of FFRB or DFRB to diets without or with exogenous xylanase on growth performance.

Experimental diet composition

A total of 532 pigs with an average initial body weight of 9.3 kg were allotted to 14 dietary treatments. The basal diet contained corn, soybean meal, and whey powder as well as 1,500 units per kg of microbial phytase. Six diets were formulated by adding 10, 20, or 30 % FFRB or 10, 20, or 30 % DFRB to the basal diet at the expense of corn and soybean meal. Seven additional diets that were identical to the initial seven diets except that they also contained 16,000 units per kg of microbial xylanase were also formulated.

All diets contained approximately 20% crude protein and 1.38% lysine. The concentration of gross energy was 4026 kcal/kg in the basal diet, and ranged from 4168 to 4375 kcal/kg in the diets containing FFRB and 4066 to 4031 kcal/kg in the diets containing DFRB.

Inclusion level of rice bran

Final body weight was not affected by the inclusion level of FFRB or DFRB (Table 1). Average daily feed intake decreased linearly (P < 0.05) as the inclusion rate of FFRB or DFRB increased. This is likely because of physical factors of rice bran, such as increased bulkiness or dustiness. Pigs fed diets containing DFRB had greater (P < 0.05) average daily feed intake than pigs fed diets containing FFRB, likely due to the greater metabolizable energy content of FFRB. The maximum average daily gain in pigs fed diets containing either FFRB or DFRB occurred at an inclusion rate of 10% (quadratic, P < 0.05). The gain:feed ratio was not affected by the inclusion of DFRB. The maximum gain:feed in pigs fed diets containing FFRB occurred at an inclusion rate of 20% (quadratic, P < 0.05). The gain:feed ratio was greater in pigs fed diets containing FFRB than in pigs fed diets containing DFRB.

Addition of microbial xylanase did not affect growth performance of pigs in this experiment.

Key points

• Increased inclusion levels of FFRB and DFRB decreased average daily feed intake.
• Inclusion of 10% FFRB or DFRB maximized average daily gain.
• Inclusion of 20% FFRB maximized gain:feed.
• Pigs fed FFRB had greater average daily gain and gain:feed than pigs fed DFRB.
• Exogenous xylanase had no effect on growth performance when added to diets containing FFRB or DFRB at inclusion levels up to 30%.

Table 1. Growth performance of pigs fed diets containing full fat rice bran (FFRB) or defatted rice bran (DFRB) ¹

¹Data include main effects from pigs fed diets without and with exogenous xylanase.
²L = linear effect of FFRB; Q = quadratic effect of FFRB.
³L = linear effect of FFRB; Q = quadratic effect of DFRB.

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