Effects of prebiotics on nutrient digestibility of a soybean-meal-based diet by red drum Sciaenops ocellatus (Linnaeus)

The present study examined the effects of four prebiotic compounds on nutrient and energy digestibility of soybean-meal-based diets by red drum (Sciaenops ocellatus). The experimental diets contained 40% crude protein of which approximately half was provided by soybean meal with the remainder from menhaden fish meal. The four prebiotics GroBiotic (R)-A (a mixture of partially autolysed brewers yeast, dairy ingredient components and dried fermentation products), mannanoligosaccharide (MOS), galacto-oligosaccharide (GOS) and inulin were individually added to the basal diet at 1% by weight. A diet with all its protein provided by menhaden fish meal was also included as a control. This control diet had the highest apparent digestibility coefficient (ADC) values - 87% for protein, 87% for lipid, 78% for organic matter and 83% for energy. The basal soybean-meal-based diet supplemented with GroBiotic (R)-A, GOS and MOS had significantly (P < 0.05) increased protein (82%, 82%, 82% respectively) and organic matter ADC values (69%, 64%, 66% respectively), compared with the basal diet (69% for protein and 49% for organic matter). However, the lipid ADC values were significantly decreased for fish fed with the diets supplemented with inulin, GOS and MOS (63%, 61%, 61% respectively) compared with the basal diet (77%) but not for those fed GroBiotic (R)-A (82%). Energy ADC values were also increased in fish fed with the GroBiotic-A (R), GOS and MOS diets (73%, 70%, 72%), compared with the basal diet (57%); however, fish fed with the inulin diet had an energy ADC value (54%) similar to that of fish fed with the basal diet. Thus, the present study is the first to demonstrate that nutrient and energy digestibility of soybean-meal-based diets by red drum can be enhanced with prebiotic supplementation.