EFFECT ON GROWTH AMD APPARENT DIGESTIBILITY OF DIETS VARYING IN GRAIN SOURCE AND PROTEIN LEVEL INMacrobrachium rosenbergii

ABSTRACT Two studies each consisting of a growth and digestibility trial were carried out to evaluate the nutritive merit of four cereal grains (corn, milo, wheat and barley) in diets formulated forMacrobrachium rosenbergii. In the first growth trial four isonitrogenous, isolipidic and isocaloric (gross energy) diets differing in their grain source were fed to prawns with an initial mean weight of 7.3±0.1 g. After 12 weeks the barley based diet produced greater growth than the wheat based diet. No significant differences in feed conversion ratios, protein efficiency ratios, or feed consumption were observed. The same diets containing 1% chromic oxide were fed to larger animals (40–50 g) to determine apparent digestibility of protein and energy. Apparent digestibility of dietary energy ranged from 76.8% to 79.1% for the four diets tested and was significantly lowest in the wheat diet. Apparent digestibility of protein ranged from 84.1% to 88.9% and did not vary significantly among diets. In the second growth trial prawns with an initial mean weight of 4.1±O. l g were fed six isolipidic, isocaloric diets varying in protein level (20%, 30% or 40%) and grain source (wheat or barley). Growth at 12 weeks was significantly different among treatments. The wheat and barley 30% and 40% protein diets supported greater growth than the 20% protein wheat diet. The 40% protein wheat diet and 30% protein barley diet supported greater growth than the 30% protein wheat diet. Higher feed consumption was observed with the higher protein diets. No differences between feed and protein conversion ratios were observed among diets. In the second digestibility trial, apparent digestible protein was not significantly different among treatments, however, digestible energy was significantly different among treatments. It appears from the results that feed consumption and apparent digestible energy contributed to the growth response observed in the two growth trials. At the 30% dietary protein level, barley appears to have been more efficiently utilized than wheat, effectively reducing the level of required dietary protein.