Industrial insect production to feed livestock is a more sustainable and less land occupying protein ingredient that may be cost effective in the future. Besides, it can be reared on organic waste, thus reducing the potential environmental load of waste streams. Prepupae of the black soldier fly (BSF), with a high value protein can potentially be incorporated in feed for monogastric animals. The BSF are also rich in fat, and 60% of it is lauric acid (C12:0) which is known for its antimicrobial effects on Gram positive bacteria. For this study, in vitro and in vivo approaches were performed. First, the effects of BSF fat on the gut microbiota were assessed in vitro by simulating piglet digestion in the upper small intestine. Different levels of BSF fat (0.12, 0.29, 0.58, and 0.87 g C12:0/100 mL) were added to an incubation medium that contained: synthetic diet, a phosphate buffer (pH 5) and a microbial inoculum from one donor piglet. It was incubated at 37 °C for 4 h. Using selective media, coliforms, D-streptococci, lactobacilli and total anaerobic bacteria were counted at the end of the incubations. Second, weaned piglets (6.18 ± 0.56 kg of BW; 21 d of age) allotted to 4 dietary treatments (7 replicates and 2 piglets/pen) were provided diets (15 d) including full-fat (4 and 8%) and defatted (5.4%) BSF prepupae and compared to a control diet (with soybean as protein and fat source). The gut microbiota, parameters for gut health, performance and digestibility of the diet were investigated.
In vitro, the 0.58 g C12:0/100 mL prepupal fat, suppressed growth of lactobacilli, although, the most substantial antibacterial effects were against D-streptococci. At the highest inclusion level (equivalent to 0.87 g C12:0/100 mL), around 2 log fold reductions of D-streptococci were observed. In vivo, only 0.5 log fold reductions were observed for D-streptococci in the gut of piglets fed BSF containing diets. Evidence of differences was not observed for daily gain, feed intake and feed to gain ratio among treatments. Similarly, the apparent fecal digestibility of the control feed did not differ significantly to that of the insect-containing feed (protein digestibility between 77 and 78%). Differently, the ileal protein digestibility of the 8% full-fat BSF diet (67.4%) was lower than that of the control (69.7%), whereas the values for the 4% full-fat and the defatted BSF diets were higher (73.3%).
In conclusion, this trial demonstrated that a substantial amount of soybean products can be replaced by BSF without adverse effects on performance. Nonetheless, future research should further focus on exploring the added value of whole BSF prepupae compared to conventional protein sources. Also, the optimization of the insect rearing systems needs to be addressed given the current price of BSF prepupae, which is substantially higher than soybean.
Spranghers, T., Michiels, J., Vrancx, J., Ovyn, A., Eeckhout, M., De Clercq, P., and De Smet, S. (2018). Gut antimicrobial effects and nutritional value of black soldier fly (Hermetia illucens L.) prepupae for weaned piglets. Animal Feed Science and Technology, 235, 33-42. https://doi.org/10.1016/j.anifeedsci.2017.08.012