A 16-day rearing trial was performed to investigate the influence of two supplemental levels (5% and 10%) of six dietary fat sources (linseed oil, peanut oil, coconut oil, soybean oil, lard oil and fish oil) on the growth, development and nutrient composition of black solider fly larvae. Our results demonstrated that the pre-pupa rate of larvae was linearly influenced by dietary C18:0, C18:3n-3 and C18:2n-6 content (pre-pupa rate = 0.927 × C18:0 content + 0.301 × C18:3n-3 content-0.258 × C18:2n-6 content p < 0.001)), while final body weight was linearly influenced by that of C16:0 (final body weight = 0.758 × C16:0 content, p = 0.004). Larval nutrient composition was significantly affected by dietary fat sources and levels, with crude protein, fat and ash content of larvae varying between 52.0 and 57.5, 15.0 and 23.8, and 5.6 and 7.2% dry matter. A higher level of C12:0 (17.4–28.5%), C14:0 (3.9–8.0%) and C16:1n-9 (1.3–4.3%) was determined in larvae fed the diets containing little of them. In comparison, C16:0, C18:1n-9, C18:2n-6 and C18:3n-3 proportions in larvae were linearly related with those in diets, with the slope of the linear equations varying from 0.39 to 0.60. It can be concluded that sufficient C16:0, C18:0 and C18:3n-3 supply is beneficial for larvae growth. Larvae could produce and retain C12:0, C14:0, and C16:1n-9 in vivo, but C16:0, C18:1n-9, C18:2n-6 and C18:3n-3 could only be partly incorporated from diets and the process may be enhanced by a higher amount of dietary fat. Based on the above observation, an accurately calculated amount of black soldier fly larvae could be formulated into aquafeed as the main source of saturated fatty acids and partial source of mono-unsaturated and poly-unsaturated fatty acids to save fish oil.

Several studies have reported an intricate link between the G protein-coupled receptor 109A (GPR109A) and intestinal health. Upon activation, induced by butyric acid and β-hydroxybutyric acid, GPR109A regulates the expression of tight junction proteins, exerts anti-inflammatory effects, and maintains the integrity of the intestinal barrier. However, its function and the mechanism of action in combating the infection caused by exogenous pathogenic microorganisms remain unclear. This study established an animal model of infection by oral enterotoxigenic Escherichia coli (ETEC) gavage to examine the underlying mechanism(s) and protective effects of GPR109A on the intestinal tract. Experimental GPR109A^–/–and GPR109A^+/+ mice were orally administered with 1 × 10⁹ colony-forming units (CFUs) of ETEC, and changes in body weight were then observed. The colonization and translocation of ETEC in the intestine were detected by the plate counting method. The expression of tight junction proteins and the levels of inflammatory factors and secretory IgA (SIgA) in the intestine were detected by quantitative real-time polymerase chain reaction (q-PCR), western blotting, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry. The results demonstrated that GPR109A^–/–mice were more susceptible to ETEC infection, showing more severe inflammatory reactions and intestinal damage. Moreover, the secretion of IgA in the intestinal tract of GPR109A^+/+ mice was significantly increased after ETEC infection, whereas the IgA levels in GPR109A^–/–mice did not change significantly. We added 5 g/L sodium butyrate to the drinking water of all mice. The GPR109A^+/+ mice were protected against ETEC infection and no effect was observed in GPR109A^–/–mice. Similarly, sodium butyrate increased the SIgA content in the gut of the GPR109A^+/+ mice and no effect was observed in GPR109A^–/–mice. In conclusion, activated GPR109A is effective against the colonization and translocation of ETEC in the gut and maintains the integrity of the intestinal barrier, possibly by promoting the secretion of intestinal IgA.

A high-quality protein substitute, Hermetia illucens (black soldier fly) larvae powder, is rich in protein and often used in animal feed. This study aimed to investigate the feasibility and optimal ratio of replacing fish meal with H. illucens larvae in weaned piglets and to demonstrate the effects on piglets' growth performance, intestinal microflora and immune performance. Forty-eight female weaned piglets were randomly classified into three groups. Each group consisted of eight pens (replicates), with two piglets per pen. Three groups containing different proportions of H. illucens larvae (0, 4, and 8%) were referred to as C, HI4, and HI8. We first designed a 28-day feeding experiment to detect growth performance; after that, the piglets were induced with oral gavage of enterotoxigenic Escherichia coli K88 (ETEC K88) and recording diarrhea on day 29 of the experiment. Samples were taken on the 32nd day to detect the effect of H. illucens larvae on the immune performance of the weaned piglets. H. illucens larvae replacement did not cause any obvious change in the growth performance nether in HI4 nor in HI8 of weaned piglets with 28 d feeding stage. H. illucens larvae could improve the intestinal health of weaned piglets by increasing the content of Lactobacillus and reducing the content of Streptococcus. Compared with C+K88 group, the diarrhea rate was attenuated for the H. illucens supplemented group. The integrity of ileum villi in HI4+K88 and HI8+K88 groups was better than that in C+K88 group, and the villi in C+K88 group were severely damaged. The expression of IL-10, Occludin and Claudin-3 in the intestinal mucosa of the HI4+K88 group and HI8+K88 group were significantly increased (P < 0.05), and the expression of TNF-α was significantly decreased (P < 0.05) compared with the C+K88 group. The results of immunoblotting also validated that the same ETEC K88 treatment of weaned piglets enhanced the expression of tight junction protein in the intestinal mucosa of the H. illucens addition group. ETEC-induced diarrhea will be reduced by the diet of weaned piglets containing H. illucens larvae, ameliorating the immune performance of piglets. Our results indicates that the optimal dosage of H. illucens replacement in weaned piglets is 4%.

Insects have been used as animal feed protein sources in livestock and poultry breeding, and their impact on pork quality needs to be studied. This experiment mainly explores the effect of adding black soldier flies to the feed on the growth performance and meat quality of pigs. All 24 weaned piglets were randomly divided into three groups, one group was given a normal diet as the control group (C), and the other two groups were supplemented with 4% (T1) and 8% (T2) black soldier flies as an alternative protein source, respectively. Pig growth performance and carcass traits were measured at the end of the 113-day experiment. After euthanizing the pigs, we used metabolomics to detect pig dorsal muscle and qPCR to detect gene expression in dorsal muscle and adipose tissue. For the average daily gain and backfat thickness, T2 group was significantly higher than T1 group and C group (p < 0.05). Intramuscular fat content was significantly elevated in the T1 and T2 groups (p < 0.05). The metabolomics results showed that there were significant differences in metabolites among the three groups (p < 0.05). The addition of black soldier flies could increase the content of some free amino acids, and the content of lipid metabolites also changed significantly (p < 0.05). The gene expression of type 1 muscle fibers in the T1 group and the PGC-1α gene expression in the T1 and T2 groups were significantly increased in the dorsal muscle (p < 0.05). The results of the present study showed that adding 4% black soldier fly instead of fish meal in the diet of growing pigs can significantly improve meat quality and supplementation of 8% black soldier flies has beneficial effects on growth performance of pigs.