Many researchers consider gut microbiota (trillions of microorganisms) an endogenous organ of its animal host, which confers a vast genetic diversity in providing the host with essential biological functions. Particularly, the gut microbiota regulates not only gut tissue structure but also gut health and gut functionality. This paper first summarized those common bacterial species (dominated by the Firmicutes, Bacteroidota, and Proteobacteria phyla) in swine gut and then briefly discussed their roles in swine nutrition and health, which include roles in nutrient metabolism, pathogen exclusion, and immunity modulation. Secondly, the current knowledge on how dietary nutrients and feed additives affect the gut bacterial composition and nutrient metabolism in pigs was discussed. Finally, how dietary amino acids affect the relative abundances and metabolism of bacteria in the swine gut was reviewed. Tryptophan supplementation promotes the growth of beneficial bacteria and suppresses pathogens, while arginine metabolism affects nitrogen recycling, impacting gut immune response and health. Glutamate and glutamine supplementations elevate the levels of beneficial bacteria and mitigate pathogenic ones. It was concluded that nutritional strategies to manipulate gut microbial ecosystems are useful measures to optimize gut health and gut functions. For example, providing pigs with nutrients that promote the growth of Lactobacillus and Bifidobacterium can lead to better gut health and growth performance, especially when dietary protein is limited. Further research to establish the mechanistic cause-and-effect relationships between amino acids and the dynamics of gut microbiota will allow swine producers to reap the greatest return on their feed investment.

Gut-brain communication via the peripheral neural network is vital for regulating local digestive function and systemic physiology. Gut microbiota, which produces a wide array of neuroactive compounds, is a critical modulator in this bidirectional dialog. Perturbations in the gut microbiota have been implicated in neurological disorders such as depression and stress. Distinct from humans and other monogastric animals, ruminants possess a unique, microbially dense gastrointestinal compartment, the rumen, that facilitates the digestion of fibrous plant materials. These ruminal microbes are likely key contributors to rumen-brain crosstalk. Unlike certain microbe-derived neuroactive compounds produced in the hindgut that are minimally absorbed and primarily excreted in feces, those generated in rumen can reach the small intestine, where they are largely absorbed and affect central nervous system through systemic regulation in addition to the vagal pathway. Notably, emerging evidence suggests that rumen microbiota dysbiosis under stress is associated with abnormal behavior, altered hormonal and neurotransmitter levels. In this review, we introduce the concept of the rumen-microbiome-brain axis by comparing the anatomical structures and microbial characteristics of the intestine and the rumen, emphasizing the neuroactive potential of rumen microbiome and underlying mechanisms. Advances in this frontier hold tremendous promise to reveal a novel dimension of the gut-microbiome-brain axis, providing transformative opportunities to improve ruminant welfare, productivity, and agricultural sustainability.

Menthol, the primary active compound in the widely cultivated peppermint plant (Mentha piperita), is well known for its use in human products such as topical analgesics and cold remedies. Menthol’s cooling sensation and ability to locally modulate pain through interactions with transient receptor potential channels make it a valuable bioactive compound. In recent years, menthol’s antimicrobial, anti-inflammatory, and antioxidative properties have drawn attention in the livestock industry as a natural alternative to synthetic antibiotics in feed additives. This review comprehensively examines the existing literature to assess menthol’s effects on animal growth performance, product quality, immune function, gastrointestinal microbial ecosystems, and metabolism across various livestock species. Notably, menthol shows potential for improving feed efficiency, mitigating chronic inflammation and oxidative stress, inhibiting environmental and gastrointestinal pathogens, and enhancing calcium absorption. However, optimal dosages, treatment durations, synergies with other phytogenic compounds, and regulatory mechanisms require further investigation. Additionally, with increasing global temperatures and growing concerns about animal welfare, menthol’s cooling, methane-reducing, and analgesic properties present promising opportunities for advancing sustainable livestock practices.

Gut microbial dysbiosis is a common cause of calf diarrhea, a major contributor to calf mortality. Additionally, the early gut microbiota in calves is cons

Gossypol is a phenolic compound found in cottonseed. Phenolic compounds are plant secondary metabolites, known to have both, beneficial and negative effects on animals. The present experiment evaluated the beneficial and negative effects of cottonseed on growth, daily weight gain, and parasite infection measured by fecal egg counts, liver function, and ruminal microbiome of growing female meat goats. Forty Boer × Spanish doelings were assigned to 4 groups (n = 10 per group) in a 2 × 2 factorial design consisting of cottonseed supplementation (CS)-NP CS (0.5% body weight-BW in kg) + no parasite infection (NP) CON-NP commercial pellets or control (CON) + no parasite infection (NP); CON-P commercial pellets or control (CON) + Haemonchus contortus artificial infection (P); and CS-P CS supplementation (CS) + H. contortus artificial infection (P). Artificial infection consisted of 4,000 H. contortus infective larvae (L3). The FEC were not affected by diet. The liver function showed a diet by parasite interaction (P = 0.03) for the mean velocity of the hepatic portal vein, which was decreased in CON-P compared with CS-NP indicating a reduction in metabolism. A diet by parasite interaction (P = 0.014) was also observed for the diameter of the hepatic portal vein, which was increased in the CS-P goats compared to all other groups. Liver weights were affected by diet, being decreased in the CS animals vs the CON ones (P = 0.00), as well as the liver weight relative to the animal’s BW (P = 0.01). Diet effect (P = 0.01) was observed for the liver blood flow relative to liver weight. For the rumen microbiome, the number of bacterial species was unaffected by CS but decreased by the parasite challenge (P = 0.03). In conclusion, the supplementation of female meat goats with CS did not affect BW, daily weight gain, parasite infection, and FAMACHA©, but reduced the liver weights, influenced fiber-digesting bacteria in the rumen, and restored lipolytic bacteria in the rumen of goats with parasite challenge.

Semen quality is a key determinant of reproductive performance in breeding boars, and emerging evidence suggests the seminal microbiome may influence sperm function. However, the composition of the seminal plasma microbiome and its relationship to sperm quality remain poorly characterized. This study aimed to investigate the microbial composition of boar seminal plasma and its association with sperm quality. Semen ejaculates collected from Duroc boars were analyzed and classified as Passed (≥70% normal morphology) or Failed (<70% normal morphology). Seminal plasma was isolated by centrifugation and analyzed using 16S/ITS rRNA gene sequencing. The dominant bacterial phyla were Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. The most abundant genera included Porphyromonas, Bacteroides, and Cladosporium. Only the Shannon diversity index was significantly higher in Failed samples for the bacterial microbiome (p = 0.038). Furthermore, correlation analysis showed a negative association between Tenericutes and sperm concentration (r = −0.90; p = 0.014). Linear discriminant analysis identified microbial biomarkers associated with sperm quality, including Rhodococcus, Sphingomonas, Lactobacillus, Streptococcus, and Empedobacter. The increased abundance of these genera in Failed samples suggests disruption of the normal seminal microbial community. In conclusion, boar seminal plasma harbors a distinct bacterial and fungal microbiome that is associated with sperm morphology.