Strategies to improve the nutritive value of rice bran in poultry diets. IV. Effects of addition of fish meal and a microbial phytase to duckling diets on bird performance and amino acid digestibility

1. Ducklings were given diets with vegetable protein (VP) and 0 or 600 g ri ce bran/kg; fish meal (60 g/kg) and a phytase (+, -) were added to the diet s (VP + AP). An additional 40 g soyabean meal/kg was added to the diet with rice bran (VP++). Amino acid digestibility and mineral retention were meas ured in the lower ileum of ducklings killed at 23 d of age. Acid insoluble ash was used as an inert marker. Trypsin and amylase activities were also m easured and weights of the pancreas and small intestine recorded at slaught er. 2. Addition of soyabean meal (VP++) to the diet with rice bran improved gro wth rate and food intake compared to the diet without (VP) and gave the sam e food intake and growth rate as the comparable basal diet (VP) without ric e bran. Fish meal improved growth rate on the diets without rice bran and i mproved food intake on this diet (VP + AP). Rice bran depressed growth rate and food conversion ratio (FCR); protein source affected growth rate, food intake and FCR; phytase increased food intake only. There were several int eractions. 3. Determined total amino acid composition of the diets appeared to meet th e essential amino acid requirements of ducklings. Rice bran depressed the i leal digestibility of virtually all amino acids and phytase had no direct e ffect, although there were interactions. Fish meal addition to diets with r ice bran improved the apparent digestibility of several essential amino aci ds as well as that of dry matter and crude protein. 4. Ileal retention of some minerals and tibia ash content were reduced by r ice bran. Fish meal and phytase inclusion increased P retention and ash in tibia. 5. Higher intestinal trypsin activity and increased pancreas size were seen in ducklings on diets with rice bran compared to those without. Intestinal amylase activity was reduced in ducklings given rice bran, probably becaus e of its low starch content. 6. The stimulating effect of fish meal on duckling performance was probably caused in part by the improvement in the digestibility of some amino acids . The addition of small amounts of minerals in fish meal may have increased mineral retention. Phytase Save benefits anticipated from our previous wor k, but also improved lysine and threonine digestibility in diets containing vegetable protein only.