Effects of extrusion of rice bran on performance and phosphorous bioavailability in broiler chickens

Rice bran, an important by-product of the rice milling industry, has the potential
to be used as an alternative to grains in the poultry diet 1]. It contains 15???22 % oil, 11???17 % protein, 6???14 % fiber, 10???15 % moisture,
and 8???17 % ash 2]; however, the presence of anti-nutritional factors such as phytic acid 3], trypsin inhibitor and hemagglutinin 4], high fiber content 5], and instability during storage 6] limit its use in poultry nutrition. Pancreatic hypertrophy 7], 8], depressed intestinal amylase activity 8], and reduction in feed consumption 9] and growth 10] have been reported as the side effects of feeding raw rice bran to broilers.

Approximately 90 % of P in rice bran is in the form of phytic acid and phytate chelated
with other elements; phytate not only does reduce P availability, but also decreases
the absorption of elements such as zinc, iron, calcium and magnesium 11]. In addition, it decreases protein digestibility and energy use through inhibition
of the enzymes such as pepsin, trypsin and ?-amylase 12], 13]. Rice bran also contains lipase and peroxide which are released during rice polishing
and cause lipid oxidation 2], 14]. Therefore, it is necessary to stabilize the rice bran by effective pretreatments
to limit the undesirable reactions 2]. The extrusion cooking technology, a thermal/mechanical pretreatment applying heat
treatment in the presence of moisture, is an effective processing method causing physico-chemical
and nutritional modifications of the food constituents, such as permanently denaturing
lipases 15]–17]. Use of extruded rice bran in the diet of broilers, compared with raw and roasted
rice bran, significantly increased fat digestibility which was attributed to lipase
and trypsin inhibitor inactivation 1], 15]. In addition, use of 10, 20 and 30 % extruded rice bran in broiler diets, compared
with raw and roasted rice bran, increased weight gain and feed consumption 6]. Sayre et al. 18] showed that feeding 600 g extruded rice bran/kg feed compared with raw rice bran,
improved broiler weight gain and feed efficiency during the first two weeks of production,
but after the second week, the performance of chicks fed the extruded rice bran was
depressed.

The poultry responses to extrusion processing of rice bran are not conclusive, especially
P availability, and more research is warranted to elucidate the dietary effect of
extruded rice bran on performance and P availability in broiler chicks. Therefore,
the present experiment was conducted to determine the effect of extruded rice bran
on performance and P availability in broiler chicks.