Abstract:

The indicator method, 0.5% or 1.0% chromic oxide, and the dissection technique of collecting feces, were used to evaluate the digestibility of protein by Oreochromis niloticus. High and low protein feedstuffs were evaluated for true and apparent digestibility coefficients in isocaloric diets formulated to contain 30% and 15% protein, respectively. The stomach and subsequent segments of the intestine were analyzed for their protein and chromic oxide content.
Results indicated that animal and plant proteins were highly available to O. niloticus. The true digestibility coefficients of tested feedstuffs were: corn gluten meal 97%; soybean meal 93%; fish meal 92%; shrimp 87%; rice bran 93%; azolla 75%; and copra meal 56%. The nonprotein diet showed that the anterior intestine was the major site of metabolic nitrogen excretion. The major site for nitrogen absorption in the intestine varied with different feedstuffs. The similar true digestibility coefficients of casein in the 15% and 30% protein diets indicated that true protein digestion was independent of dietary protein level.
The effects of fat, carbohydrate and energy levels on protein digestibility were determined in a 2 x 2 factorial experiment using two levels of energy (2,800 kcal•kg-1 and 3,800 kcal•kg^-1) and two levels of fat (6% and 12%), at 30% protein. Increase in fat level from 6% to 12% had no effect on protein digestibility at 2,800 kcal•kg^-1 energy level. High energy diets giving protein:energy ratios below 83 mg• kcal ^-1 yielded significantly (P ≤ 0.05) lower protein digestibility. The results suggest that dietary fat up to 12% provides energy of O. niloticus to spare protein as an energy source without negatively affecting protein digestibility.

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Date 1989/06/01

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