Abstract

R i c e bran has received increased attention as a feedstuff for swine and as a source of oil for human consumption. Depending on milling conditions and hull contamination, bran from California rice contains 15 to 20 percent oil, 30 to 40 percent digestible carbohydrate, and 12 to 14 percent protein, although levels of up to 18 percent protein have been reported. Rice bran is also an excellent source of vitamins and minerals. Two problems may be encountered, however, when feeding rice bran to swine: (1) It contains high levels of phytic acid; levels of 5 percent or more have been reported. (2) Milling activates an enzyme system that rapidly degrades the oil to free fatty acids and glycerol. The adverse effects of dietary phytic acid have long been recognized. Although cereal grains are high in phosphorus, 60 to 80 percent of that is present as phytic acid phosphorus, only 25 percent of which, on average, is available to the pig. A larger problem associated with feeding diets containing high levels of phytic acid is its capacity to irreversibly bind trace elements such as zinc and iron. Previous research from this laboratory demonstrated that when wheat-soybean oil meal diets containing 40 percent raw rice bran were fed to growing pigs, some animals developed parakeratosis, a typical zinc deficiency symptom, characterized by a scaly type of dermatitis. Enzymatic degradation of rice bran oil begins immediately, when activated by milling. Although the rate of hydrolysis varies with temperature and other factors, approximately 30 percent of the oil is degraded to free fatty acids during a week of storage under tropical conditions. The increased concentration of free fatty acids has two disadvantages: (1) It dramatically lowers the yield of edible oil, if the oil is to be extracted for human consumption. (2) It is likely to decrease palatability if the bran is fed to livestock, and ultimately may lower feed intake. Research has shown that the enzymes responsible for degrading rice bran oil can be destroyed by heat, allowing the bran to be stored for several months. A bran stabilization process has recently been developed by the Western Regional Research Center, US. Department of Agriculture, in which rice bran is heated for about 3 seconds to 130°C in an extrusion cooker then held at about 100°C for 3 minutes before cooling. This treatment permanently inactivates the lipolytic enzyme system in the milled bran and prevents any increase in free fatty acid content of the oil. Although rice bran is widely used as a livestock feed in tropical regions, its full feeding value is often not realized because of deterioration during storage and incorrect ration formulation. Raw rice bran is used to replace a portion of the dietary grain, although the degree of replacement possible has not been well defined owing to inconsistent results. In some cases, 30 percent raw rice bran improved pig performance, while other research demonstrated that 20 percent rice bran diets decreased feed efficiency. More recently, researchers in Florida reported that up to 30 percent raw rice bran in a maize-soybean oil meal diet did not affect weight gain in swine, but higher levels decreased weight gain and feed efficiency. In research conducted at the University of Hawaii, 40 percent raw bran in corn-soy diets did not adversely affect growth or feed efficiency of growing-finishing pigs, but higher levels of bran reduced growth. They also reported that the apparent digestibility of both dietary protein and energy components decreased as dietary levels of raw rice bran increased. These results were all obtained with diets supplemented with raw rice bran produced at some previous unreported time. Furthermore, there was no indication of the type of storage or any estimation of the amount of bran oil that might have undergone hydrolysis, although in some cases it was stated that the bran had been produced outside the state. Rice bran thus treated would be likely to have higher levels of free fatty acids than stabilized bran. Some limited information exists on the feed value of stabilized rice bran for growing swine. Feeding trials in Spain with growing-finishing pigs compared a control ration composed mainly of sorghum, corn, and soybean meal and an experimental ration that substituted 20 percent stabilized rice bran for part of the corn and sorghum. Stabilized rice bran at that level did not significantly affect growth or feed efficiency. It should be noted that the stabilized bran fed had been in storage two to three months. At the University of California, Davis, a pilot study compared raw and stabilized bran at 20 and 40 percent levels in cornsoy rations for effects on growth and feed efficiency of swine. Five purebred Duroc barrows were assigned to each of five dietary treatments for a 92-day growth study. The control diet was ti corn-soy ration supplemented with 20 percent fatfree stabilized rice bran (table 1). Although statistical analysis indicated no differences in the measured parameters (as a consequence of the small number of animals), pigs fed the 40 percent stabilized bran diet had the lowest weight gain among treatment groups but better feed efficiency than pigs fed a similar level of raw rice bran. The modern crossbred pig would probably grow faster and utilize feed more efficiently than did pigs in any of the aforementioned research.

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