Nutritional assessment of Australian canola meals. II. Evaluation of the influence of the canola oil extraction method on the protein value of canola meals fed to the red seabream (Pagrus auratus, Paulin)

Abstract

This study examined the biological value of expeller- and solvent-extracted canola meals when included in the diets of juvenile red seabream. Notably, the test and reference diets in this study were prepared to be protein (300 g kg−1 DM) and energy (16.5 MJ kg−1 DM) limiting. Test diets were prepared, in which canola meal provided either 20%, 40% or 60% of the total dietary digestible protein. To minimize the influence of compensatory feed intake, all diets were pair-fed to the fish on restricted basis. Positive and negative controls were also included as treatments in the study to demonstrate that the diets were protein limiting and also to demonstrate the relative value of the highest inclusion levels of each test ingredient. The canola meals, either expeller- or solvent-extracted, were found to be nutritionally useful in diets for red seabream. Both ingredients were of similar value to that of the soybean meal when included on an equivalent digestible protein basis. No significant differences in weight gain, survival, FCR, N retention, energy retention or the apparent biological value of the N content were observed among any of the groups receiving the test or reference diets. A few significant differences were observed among some of the test and reference diets with regard to the apparent biological value of their energy content, although no consistent pattern was evident. The positive control treatment supported significantly superior growth and food utilization by the fish relative to all other treatments. The negative control treatment resulted in significantly poorer growth and food utilization by the fish relative to all other treatments. On a relative basis, there were no declines in fish performance between the highest inclusion levels of the expeller- and solvent-extracted canola meals or the soybean meal. Hence, the fish in this study obtained equivalent nutritional value from these ingredients, on a digestible basis, to that of the fishmeal in the reference diet.