Nutritive value of feed substrate waste from black soldier fly larvae production, and its potential as an aquafeed ingredient

Black soldier fly larvae (BSFL, Hermetia illucens) are an alternative source of protein for aquaculture whereas the feed substrate waste (FSW) from larval production is valueless and has never been evaluated for application in animal feed. The nutritive value and physicochemical properties of FSW from BSFL were here investigated in vitro. Ten-day-old first-instar larvae were cultivated on two feed substrates: laying hen feed (FS I) or a laying hen feed-rice bran blend (1:1 w/w, FS II). FSW samples were collected at day 4.5 (0.5FSW) and day 9 (1FSW) of larval rearing, and compared to the original feed substrate (0FSW). Crude protein increased dependent on FS type, harvesting time (HT), and their interaction. Crude lipid, crude fiber, acid detergent fiber, neutral detergent fiber, crude ash, nitrogen-free extract, and gross energy decreased (P < 0.05). Analysis of the physicochemical properties of FSW by various techniques (scanning electron microscopy, differential scanning colorimetry, X-ray diffractometry, and Fourier transform infrared spectrometry) revealed qualitative and quantitative changes in FSW driven by biological processes of BSFL. The digestibility of protein in FSW was determined by an in vitro protein digestibility (IVPD) test using crude digestive enzyme extracts from Nile tilapia (Oreochromis niloticus) and striped catfish (Pangasianodon hypophthalmus). 1FSW from FS I showed significantly better availability of protein relative to 0.5FSW (P < 0.05), while the IVPD of FSW from FS II was stable (P > 0.05) or reduced (P < 0.05). Findings from this study suggest FSW from BSFL cultivation could be a protein source in aquafeed.