Enhancing pig growth and gut health with fermented Jatropha curcas cake: Impacts on microbiota, metabolites, and neurotransmitters

Given the escalating global crisis in feed protein availability, Jatropha curcas L. cake has attracted significant interest as a viable alternative protein source in animal feed. This experiment was conducted to investigate the effects of fermented Jatropha curcas L. cake (FJCC) as a protein feed in the diet of pigs. A total of 96 growing pigs with an average weight of 27.60 ± 1.59 kg were divided into three dietary groups with varying FJCC inclusion levels (0, 2.5, and 5%) for a 28 d trial. Results showed that the diet with 5% FJCC (FJCC5) demonstrated significant improvements in average daily gain (p = 0.009), feed-to-gain ratio (p = 0.036), nutrient digestibility, and intestinal morphology. Furthermore, the FJCC5 diet resulted in a decrease in pH values in different gut sections (jejunum p = 0.045, cecum p = 0.001, colon p = 0.012), and favorably altered the profile of short-chain fatty acids (SCFAs) with increased butyric acid content (p = 0.005) and total SCFAs (p = 0.019). Additionally, this diet notably decreased IL-6 levels in the jejunum (p = 0.008) and colon (=0.047), significantly reduced IL-1 levels in the hypothalamus (p < 0.001), and lowered IL-1, IL-6, and IL-10 levels in plasma (p < 0.05). Microbiota and metabolite profile analysis revealed an elevated abundance of beneficial microbes (p < 0.05) and key metabolites such as 4-aminobutyric acid (GABA) (p = 0.003) and serotonin (5-HT) (p = 0.022), linked to neuroactive ligand-receptor interaction. Moreover, FJCC5 significantly boosted circulating neurotransmitter levels of 5-HT (p = 0.006) and GABA (p = 0.002) in plasma and hypothalamus, with corresponding increases in precursor amino acids (p < 0.05). These findings suggest that FJCC, particularly at a 5% inclusion rate, can be an effective substitute for traditional protein sources like soybean meal, offering benefits beyond growth enhancement to gut health and potentially impacting the gut-brain axis. This research underscores FJCC's potential as a valuable component in sustainable animal nutrition strategies.