The composition and abundance of microorganisms in the gastrointestinal tract of cows are complex and extensive, and they play a crucial role in regulating nutrient digestion, absorption, maintaining digestive tract stability, and promoting the production and health of the host. The fermentation carried out by these microorganisms in the gastrointestinal tract is fundamental to the health and productivity of cows. Rumen microorganisms produce the majority of enzymes required to break down feed substrates, such as cellulose, protein, lipids, and other plant materials, through fermentation. This process provides energy metabolism substrates that satisfy approximately 70% of the host’s energy requirements for physiological activities. Gut microorganisms primarily decompose cellulose that is difficult to digest in the rumen, thereby providing heat and energy to the hosts. Additionally, they have an impact on host health and productivity through their role in immune function. Understanding the composition and function of the cow gut microbiota can help regulate dairy cattle breeding traits and improve their health status. As a result, it has become a popular research topic in dairy cattle breeding. This article provides a review of the composition, structure, physiological characteristics, and physiological effects of the cow gut microbiota, serving as a theoretical foundation for future studies that aim to utilize the gut microbiota for dairy cattle breeding or improving production traits. It may also serve as a reference for research on gut microbiota of other ruminants.

This study aimed to evaluate the effectiveness of oral gavage of dextran sodium sulfate (DSS) to establish an enteric inflammation model in broilers. Forty 1-day-old male, yellow-feathered broilers were randomly divided into 2 groups with 5 replicates of 4 birds each for a 42-day trial. The experiment design used 2 groups: (1) the control group (CT), normal broilers fed a basal diet, and (2) the DSS group, DSS-treated broilers fed a basal diet. The DSS group received 1 mL of 2.5% DSS solution once a day by oral gavage from 21 to 29 days of age. The results showed that compared with those in CT, DSS treatment significantly increased histological scores for enteritis and mucosal damage at 29 and 42 days of age (p < 0.01) and the disease activity index (DAI) from 23 to 29 days of age (p < 0.01). DSS-treated broilers showed poor growth performance at 42 days of age, including decreased body weight and average daily gain and an increased feed conversion ratio (p < 0.01). DSS also caused gross lesions and histopathological damage in the jejunum of broilers, such as obvious hemorrhagic spots, loss of villus architecture, epithelial cell disruption, inflammatory cell infiltration, and decreased villus height. These results suggest that oral gavage of DSS is an effective method for inducing mild and non-necrotic enteric inflammation in broilers.

Background: Yak cows produce higher quality milk with higher concentrations of milk fat than dairy cows. Recently, studies have found the yak milk yield and milk fat percentage have decreased significantly over the past decade, highlighting the urgency for yak milk improvement. Therefore, we aimed to analyze how the gut microbiome impacts milk fat synthesis in Zhongdian yak cows. Methods: We collected milk samples from Zhongdian yak cows and analyzed the milk fat percentage, selecting five Zhongdian yak cows with a very high milk fat percentage (>7%, 8.70 ± 1.89%, H group) and five Zhongdian yak cows with a very low milk fat percentage (<5%, 4.12 ± 0.43%, L group), and then obtained gut samples of these ten Zhongdian yak cows through rectal palpation. Gut metagenomics, metabolomics, and conjoint metagenomics and metabolomics analyses were performed on these samples, identifying taxonomic changes, functional changes, and changes in gut microbes-metabolite interactions within the milk fat synthesis-associated Zhongdian yak cows gut microbiome, to identify potential regulatory mechanisms of milk fat at the gut microbiome level in Zhongdian yak cows. Results: The metagenomics analysis revealed Firmicutes and Proteobacteria were significantly more abundant in the gut of the high-milk fat Zhongdian yak cows. These bacteria are involved in the biosynthesis of unsaturated fatty acids and amino acids, leading to greater efficiency in converting energy to milk fat. The metabolomics analysis showed that the elevated gut metabolites in high milk fat percentage Zhongdian yak cows were mainly enriched in lipid and amino acid metabolism. Using a combined metagenomic and metabolomics analysis, positive correlations between Firmicutes (Desulfocucumis, Anaerotignum, Dolosiccus) and myristic acid, and Proteobacteria (Catenovulum, Comamonas, Rubrivivax, Marivita, Succinimouas) and choline were found in the gut of Zhongdian yak cows. These interactions may be the main contributors to methanogen inhibition, producing less methane leading to higher-efficient milk fat production. Conclusions: A study of the gut microbe, gut metabolites, and milk fat percentage of Zhongdian yak cows revealed that the variations in milk fat percentage between yak cows may be caused by the gut microbes and their metabolites, especially Firmicutes-myristic acid and Proteobacteria-choline interactions, which are important to milk fat synthesis. Our study provides new insights into the functional roles of the gut microbiome in producing small molecule metabolites and contributing to milk performance traits in yak cows.

This study investigated the regulatory mechanism of myristic acid on milk fat synthesis in cows. An association between myristic acid and high milk fat content in Zhongdian yaks’ guts was found through combined metagenomic and metabolomic analysis. Bovine mammary epithelial cells (MAC-T) were cultured and treated with various myristic acid concentrations. After 24 h, the protein expression levels of CD36 (membrane glycoprotein CD36), ADFP (adipose differentiation-related protein), and UB (ubiquitin) were analyzed, along with cellular proteasome activity, triglyceride content, lipid droplets, and cell viability. Myristic acid at 200 μM significantly upregulated CD36, ADFP, UB, the content of triglyceride content and lipid droplets, and cell viability, but did not affect proteasome activity. Pathway analysis revealed that myristic acid regulates milk fat synthesis through ubiquitination–lysosome and ubiquitination–proteasome pathways. The study demonstrates myristic acid’s role in regulating triglyceride synthesis in MAC-T cells and its potential application as a feed additive for cattle, benefitting the dairy industry’s milk production efficiency and economic outcomes.

This study aims to investigate the regulatory mechanism of choline (CH) on triglyceride (TG) synthesis in cows, with a specific focus on its potential association with high milk fat percentage in the gut of the Zhongdian yak. By employing combined metagenomics and metabolomics analysis, we establish a correlation between CH and milk fat production in yaks. Bovine mammary epithelial cells (MAC-T) were exposed to varying CH concentrations, and after 24 h, we analyzed the expression levels of key proteins (membrane glycoprotein CD36 (CD36); adipose differentiation-related protein (ADFP); and ubiquintin (UB)), cellular TG content, lipid droplets, and cell vitality. Additionally, we evaluated the genes potentially related to the CH-mediated regulation of TG synthesis using real-time qPCR. CH at 200 μM significantly up-regulated CD36, ADFP, UB, and TG content. Pathway analysis reveals the involvement of the ubiquitination pathway in CH-mediated regulation of TG synthesis. These findings shed light on the role of CH in controlling TG synthesis in MAC-T cells and suggest its potential as a feed additive for cattle, offering possibilities to enhance milk fat production efficiency and economic outcomes in the dairy industry.

Milk fat content is a polygenic commercially important quantitative trait in ruminants. In recent decades, an increasing number of genes involved in milk fat synthesis have been identified through genome-wide association studies and validated using functional assays such as gene knockdown or overexpression. However, functional validation assays have been limited to small number of related genes, yielding insufficient data to fully understand the many different genes and biological processes in milk fat synthesis. To provide a comprehensive evaluation of the genes involved in milk fat synthesis, we performed a meta-analysis of 1, 395 effect sizes from 81 publications, which included 137 genes, spanning 4 ruminant species. In the studies analyzed knockdown/overexpression of candidate genes significantly reduced/increased Target Gene (Protein) and Related Gene (Protein) expression, and these effects were consistent across species. However, the effects of knockdown/overexpression of candidate genes across the different pathways of milk fat synthesis varied between species. Pathways related to milk fat synthesis, SREBP-, PPAR-, JAK-AKT- and the Insulin-pathway exhibited the largest effects on the synthesis of triglyceride, lipid droplet, cholesterol and unsaturated fatty acids, respectively. Key genes in these pathways, SREBPs (SREBP1, SREBF1), PPARs (PPARA, PPARD, PPARG), JAK2, STAT5α and INSIGs (INSIG1 and INSIG2) also have a greater effect on regulating the formation of triglyceride, cholesterol, lipid droplets and unsaturated fatty acids. Overall, our findings indicated that milk fat synthesis is regulated by multiple pathways and many different genes. Further studies are needed to confirm these findings and to understand the mechanisms underlying species- and pathway-specific responses during milk fat synthesis.