Feeding and growth stimulation of Penaeus vannamei juveniles: Dose-response to the microbial biomass NovaqProTM in practical diets

Microbial-based ingredients are gaining in popularity due to their nutritional value and functional properties. The microbial biomass Novacq (TM) (CA) and commercially produced NovaqPro (TM) produced in Australia (RA) and Thailand (RT) were assessed at various inclusion rates (2.5-15%) in a basal practical formulation as part of a dose-response study in P. vannamei. The aims were to understand their effect on feed intake and growth performance, their contribution to dietary minerals, their capacity to improve macronutrient retention efficiency, their possible impact on body composition, and ultimately their optimum inclusion rates. Nineteen iso-nitrogenous and isocalorific diets were fed over 42 days to apparent satiation to 78 tanks each containing 15 juvenile P. vannamei (0.69 g). Shrimp performed well with high survival >91% and weight gain achieved on the basal diet (0.21 g d(-1)) improved on all treatments (except 2.5% CA) up to 30% higher for CA and 60% higher for RA and RT. The growth responses were curvilinear and a plateau in growth performance was determined at 8.9 +/- 0.6% and 12.8 +/- 1.2% NovaqPro (TM) inclusion rates for broken-line and quadratic models, respectively. The response plateaued earlier at circa 7.5% inclusion for the original Novacq (TM). FCR (1.33 average) and nutrient retention efficiency (RE average of 33%, 21% and 23% for crude protein, total lipid and gross energy respectively), were largely unaffected by inclusion rates up to 10%. The highest energy retention efficiency was achieved in feeds containing 7% NovaqPro (TM). Feed intake stimulation was the major mode of action of the microbial biomass in this study, with feed intake, from as early as day 5, mirroring the growth trends. The graded inclusions of NovaqPro (TM) in diets also resulted in increases in dietary mineral composition which correlated to culture performance. However, further comparative analyses between the response against CA and RA/RT demonstrated that the supply of biologically relevant macro and micro minerals from the microbial biomass was unlikely on its own to be the primary driver of the dose-response observed. Inclusions between 7% and 9% of NovaqPro (TM) in practical diets to achieve the highest performance and nutritional benefits are recommended.