Utilization of rice bran in diets for domestic fowl and ducklings

Abstract

Rice bran constitutes about 10% of brown rice and is used as an animal feed. There are 40–45 million tonnes of rice bran produced annually, mainly in the Far East and South-east Asia. In these areas hull adulteration can occur, reducing the quality of the bran. This can now be detected by a simple colormetric method. Rancidity is a major problem due to the high oil content of the bran. Rapid hydrolysis of the oil is followed by oxidation with the changes being accelerated in warm, humid conditions. The effects on nutritive value and acceptability are unclear. An analysis of Australian produced rice bran (on a dry matter basis) gives a mean crude protein concentration of 150 g/kg, ether extract of 220 g/kg and neutral detergent fibre of 220 g/kg. The amino acid profile is generally superior to that of cereal grains. Digestibility of the oil is much less in young chickens than in adult birds resulting in a 28–35% lower metabolizable energy (ME) depending on cultivar. Equations for predicting the ME of rice bran for birds at different ages, and chemical components from rice hull content of rice bran are given. Digestibility of amino acids in rice bran is also lower for young chickens than adult birds. Inclusion of rice bran in chicken diets in excess of 20% frequently depresses growth, but higher levels can be tolerated by ducklings. Results with ducklings suggest that the composition of the basal diet to some extent influences the response of birds when rice bran is included in the diet. The inclusion of animal protein elicits an improved performance compared with that of an all-vegetable based diet. Defatted rice bran (DFRB) gives the same performance as full fat bran when equalized for ME. Laying birds can tolerate high levels of rice bran. Although some reports indicate successful inclusion of well above 600 g/kg, a practical upper limit of 450 g/kg seems to be accepted. Defatted rice bran at 250 g/kg diet resulted in leg problems, increased mortality and reduced egg output. Shell grit alleviated the problem. So far, attempts to improve the nutritive value of rice bran through addition of feed enzymes have had limited success. Feed phytase has been successful in releasing phosphorus from phytate in rice bran which is present at up to 50 g/kg dry matter. Improving the nutritional value of rice bran by heat treatment is probably not economical, although extrusion cooking will stabilize the oil before extraction and is used to stabilize rice bran for human food. Feed enzymes may be effective when a suitable combination is found.

Keywords::

• Chickens
• ducklings
• rice bran
• feed enzymes
• chemical analyses
• antigrowth factors
• fat-extracted bran
• byproduct