Rice bran is the main coproduct of the production of white rice for human consumption, and is used in livestock diets around the world. Rice bran can be full fat (FFRB), with 14 to 25% fat, or defatted (DFRB), containing 3 to 5% fat.

The type of fat in the diet affects the quality of fat in the pig, because pigs deposit fatty acids in approximately the same proportions as they exist in the diet. A high consumption of unsaturated fat can inhibit the pig's own synthesis of fat, which tends to be more saturated. The amount of unsaturated fatty acids  in fat can be expressed using the iodine value (IV), where high IVs correspond to more unsaturated fat. Increased IV in pig fat can lead to softer bellies, which are less valuable due to reduced shelf life, increased susceptibility to oxidative damage, and reduced belly sliceability.

Rice bran is high in unsaturated fatty acids, particularly oleic and linoleic acids, but there is a lack of information about how the fat in FFRB affects meat and carcass quality in finishing pigs. There is also a lack of information about how DFRB and FFRB affect growth performance of growing-finishing pigs. Therefore, an experiment was conducted to test the hypothesis that inclusion of up to 30% FFRB or DFRB in diets fed to growing-finishing pigs does not have a negative effect on growth performance, carcass characteristics, fresh meat quality, or fat quality.

Diets

A total of 224 barrows and gilts with an average initial body weight of 28.24 kg were used in this experiment. A three-phase feeding program was used. Grower diets were fed from day 0 to 35, early finisher diets were fed from day 36 to 70, and late finisher diets were fed from day 70 to 105. Seven diets were formulated within each phase: a basal diet containing corn and soybean meal, 3 diets containing corn, soybean meal and 10, 20, or 30% of FFRB and 3 diets containing corn, soybean meal and 10, 20, or 30% DFRB. All diets were formulated to meet or exceed growing pigs' requirements for all nutrients, and to contain equivalent concentrations of crude protein and digestible amino acids.

Growth performance

In all three phases, average daily feed intake (ADFI) was greater (P < 0.05) and the gain:feed ratio (G:F) was less (P < 0.05) in pigs fed DFRB compared with pigs fed FFRB (Table 1). In the grower phase, inclusion of either FFRB or DFRB did not affect ADFI, average daily gain (ADG), or G:F compared with the control diet. In both the early finisher and late finisher phases, ADFI increased (P < 0.05, linear) and G:F decreased (P < 0.05, linear) as DFRB inclusion increased. In the late finisher phase, ADFI also decreased (P < 0.05, linear) as FFRB inclusion increased.

For the overall experimental period, no effect of feeding either FFRB or DFRB on final body weight or ADG was observed. ADFI increased (P < 0.05, linear) and G:F decreased (P < 0.05, linear) as DFRB inclusion increased, whereas the opposite was true when FFRB was included in the diets. Pigs fed diets containing FFRB had lower (P < 0.05) ADFI and greater (P < 0.05) G:F compared with pigs fed DFRB.

Carcass characteristics and loin and fat quality

There were no effects of dietary treatments on any of the carcass characteristics measured (Table 2). Looking at meat quality, marbling score decreased (P < 0.05, linear) as inclusion of FFRB or DFRB increased, and the marbling score was greater (P < 0.05) in pigs fed DFRB than in pigs fed FFRB. Meat from pigs fed DFRB was lighter (greater L*, P < 0.05) than meat from pigs fed FFRB, but no other differences in color of meat were observed. Meat from pigs fed DFRB also had greater (P < 0.05) cooking loss than meat from pigs fed FFRB. Protein percentage increased (P < 0.05, linear) and lipid percentage decreased (P < 0.05, linear) with inclusion of either FFRB or DFRB. No other differences in meat quality were observed with inclusion of FFRB or DFRB.

 Belly length decreased (P < 0.05, linear) with increasing inclusion of FFRB, and decreased at 10% inclusion of DFRB but increased at 20% (P < 0.05, quadratic). The flop distance of bellies from pigs fed diets containing FFRB or DFRB increased until 20% inclusion and then decreased (P < 0.05, quadratic) indicating that belly fat was softer if rice bran was included in the diets. Yellowness, expressed as b*, decreased (P < 0.05, linear) as inclusion of DFRB increased.

The IV of belly fat increased (P < 0.05, linear) as the inclusion rate of FFRB increased in the diet, from 64.58 in pigs fed the basal diet to 77.14 in pigs fed 30% FFRB. This is probably because the FFRB diets contained more fat (up to 8.36% in the 30% FFRB grower diet) than the basal or DFRB diets (3.44 -to– 4.47%), so pigs synthesized less fat. However, feeding up to 30% DFRB  did not affect IV.

Key points

• There was no effect of inclusion of rice bran on final body weight or average daily gain over the growing-finishing period, but feeding FFRB increased G:F whereas feeding DFRB reduced  G:F.
• Inclusion of rice bran did not affect carcass characteristics.
• Feeding rice bran resulted in increased protein and decreased fat in the loin, but there was a reduction in marbling.
• Pigs fed FFRB had softer bellies and greater IV in carcass fat than pigs fed DFRB or a corn-soybean based diet.

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

Table 2. Carcass characteristics in growing pigs fed basal diets or diets containing full fat rice bran (FFRB) or defatted rice bran (DFRB)

Table 3. Meat quality of growing pigs fed basal diets or diets containing full fat rice bran (FFRB) or defatted rice bran (DFRB)

¹National Pork Producers Council (1999).
²National Pork Producers Council (1991).
³L* is a measure of darkness to lightness, a* is a measure of redness, b* = is a measure of yellowness.
⁴WBSF = Warner Bratzler shear force.

Table 4. Fat quality in growing pigs fed basal diets or diets containing full fat rice bran (FFRB) or defatted rice bran (DFRB)

¹Thickness was average of measurements taken at 8 locations from the anterior to posterior, with 4 measurements on each of the dorsal and ventral edges, respectively.

²L* is a measure of darkness to lightness, a* is a measure of redness, b* = is a measure of yellowness.

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