Animal (Sep 2024)
Effects of brewery by-products on growth performance, bioconversion efficiency, nutritional profile, and microbiota and mycobiota of black soldier fly larvae
Abstract
Brewery by-products are recognised as suitable rearing substrates for Hermetia illucens, better known as black soldier fly (BSF) but information about the impact of different ratios of brewer’s spent grains (BSG) and brewer’s spent yeast (BSY) are still scarce. This study evaluated the effects of BSG-BSY-based diets on BSF larval growth, survival, bioconversion efficiency, nutritional profile, and microbiota and mycobiota. A total of 3 000 6-day-old BSF larvae were allotted to five dietary treatments (six replicate boxes/diet, 100 larvae/box): (i) BSY2.5 (25 g/kg of BSY+975 g/kg of BSG), (ii) BSY5 (50 g/kg of BSY+950 g/kg of BSG), (iii) BSY7.5 (75 g/kg of BSY+925 g/kg of BSG), (iv) BSY10 (100 g/kg of BSY+900 g/kg of BSG), and (v) control (Gainesville diet). Larval weight and substrate pH were recorded every 4 days. At the end of the trial (5% of prepupae), bioconversion efficiency corrected for residue (BER), reduction rate (RR), and waste reduction index (WRI) were calculated, and the larval proximate composition, microbiota and mycobiota characterised. At 10 and 14 days of age, BSY7.5 and BSY10 larvae displayed higher weight than BSY2.5 and BSY5 (P 0.05). The BSY10 larvae displayed lower ether extract content than the other BSG-BSY-based diets (P > 0.001). The use of BSG-BSY-based diets did not influence the alpha diversity of larval microbiota and mycobiota (P > 0.05), but a specific microbial signature was identified per each dietary treatment (Porphyromonadaceae [BSY5], Sphingomonas [BSY7.5], Bacillus [BSY10] and Ruminococcus and Myroides [BSG-BSY-based diets]; P < 0.05). Co-occurrence and co-exclusion analysis also showed that Saccharomyces cerevisiae and Pichia excluded and favoured, respectively, the presence of Streptomyces and Fluviicola, while Clavispora lusitaniae was associated with Myroides (P < 0.05). In conclusion, BSG-BSY-based diets are suitable for rearing HI in terms of larval performance, nutritional profile, and microbiota and mycobiota, with 7.5 and 10% of BSY inclusion levels being able to improve larval growth and bioconversion efficiency.
