Short-chain fatty acids (SCFAs) are metabolites generated by bacterial fermentation of dietary fiber (DF) in the hindgut. SCFAs are mainly composed of acetate, propionate and butyrate. Many studies have shown that SCFAs play a significant role in the regulation of intestinal health in poultry. SCFAs are primarily absorbed from the intestine and used by enterocytes as a key substrate for energy production. SCFAs can also inhibit the invasion and colonization of pathogens by lowering the intestinal pH. Additionally, butyrate inhibits the expression of nitric oxide synthase (NOS), which encodes inducible nitric oxide synthase (iNOS) in intestinal cells via the PPAR-γ pathway. This pathway causes significant reduction of iNOS and nitrate, and inhibits the proliferation of Enterobacteriaceae to maintain overall intestinal homeostasis. SCFAs can enhance the immune response by stimulating cytokine production (e.g. TNF-α, IL-2, IL-6, and IL-10) in the immune cells of the host. Similarly, it has been established that SCFAs promote the differentiation of T cells into T regulatory cells (Tregs) and expansion by binding to receptors, such as Toll-like receptors (TLR) and G protein-coupled receptors (GPRs), on immune cells. SCFAs have been shown to repair intestinal mucosa and alleviate intestinal inflammation by activating GPRs, inhibiting histone deacetylases (HDACs), and downregulating the expression of pro-inflammatory factor genes. Butyrate improves tight-junction-dependent intestinal barrier function by promoting tight junction (TJ) assembly. In recent years, the demand for banning antibiotics has increased in poultry production. Therefore, it is extremely important to maintain the intestinal health and sustainable production of poultry. Taking nutrition strategies is important to regulate SCFA production by supplementing dietary fiber and prebiotics, SCFA-producing bacteria (SPB), and additives in poultry diet. However, excessive SCFAs will lead to the enteritis in poultry production. There may be an optimal level and proportion of SCFAs in poultry intestine, which benefits to gut health of poultry. This review summarizes the biological functions of SCFAs and their role in gut health, as well as nutritional strategies to regulate SCFA production in the poultry gut.

Plant tannins are widely found in plants and can be divided into hydrolyzed tannins and condensed tannins. In recent years, researchers have become more and more interested in using tannin-rich plants and plant extracts in ruminant diets to improve the quality of animal products. Some research results show that plant tannins can effectively improve the quality of meat and milk, and enhance the oxidative stability of the product. In this paper, the classification and extraction sources of plant tannins are reviewed, as well as the biological functions of plant tannins in animals. The antioxidant function of plant tannins is discussed, and the influence of their structure on antioxidation is analyzed. The effects of plant tannins against pathogenic bacteria and the mechanism of action are discussed, and the relationship between antibacterial action and antioxidant action is analyzed. The inhibitory effect of plant tannins on many kinds of pathogenic viruses and their action pathways are discussed, as are the antiparasitic properties of plant tannins. The anti-inflammatory action of tannins and its mechanism are analyzed. The function of plant tannins in antidiarrheal action and its influencing factors are discussed. In addition, the effects of plant tannins as feed additives on animals and the influencing factors are reviewed in this paper to provide a reference for further research.

In this study, 192 female broilers (21 days old) were allocated to four dietary treatments: a control diet [CT], and three experimental diets containing 25 g/kg alfalfa meal [AM25], 50 g/kg alfalfa meal [AM50], and 75 g/kg alfalfa meal [AM75]. Final body weight and average daily feed intake of birds were significantly higher in alfalfa supplemented birds, with a linear response to alfalfa inclusion seen for average daily gain (P < 0.05). Serum triglycerides were comparatively lower in AM50 group than in CT group (P < 0.05). The total weight and gastrointestinal tract indices were higher in AM75 and AM50 and sequentially lower in AM25 and CT (P < 0.05). The AM75 and AM50 treatments resulted in significantly lower pH in the duodenum and caecum than in the CT (P < 0.05). The yield percentage of half-eviscerated AM75 chickens was significantly higher than that of CT (P < 0.05). However, breast muscle percentage was significantly lower in AM75 than in CT (P < 0.05). AM diets resulted in an increased yellowness of the muscles. It was concluded that AM improved the growth performance, development of the intestine, and meat yellowness, and reduced the pH of the intestine and serum triglycerides.

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.

Cotton straw is used as a roughage source in conjunction with maize in draught prone regions in the world for animal production. However, this diet generally contains relatively low rumen degradable protein compared with its supply of fermentable metabolizable energy; therefore leading to a suboptimal animal performance and high methane production. Although urea supplementation is known to improve microbial crude protein (MCP) production and animal production, the recommended levels of urea supplementation range between 1% and 6.7% according to literatures. This in vitro study was conducted as a preliminary investigation to determine the impact of urea supplementation up to 3% (as dry matter in the diet) on rumen fermentation characteristics and protozoa population, on typical maize meal and cotton straw-based diet used for sheep production in XinJiang province, China. MCP production was improved by 64% when urea increased from 0% to 2% in the diet, with no additional benefit observed at 3% urea in the diet. On the other hand, methane production was reduced when urea increased from 0% to 3% in the diet. These results indicated that 2% urea supplemented under the current feeding condition may improve MCP production and reduce methane production. However, further in vivo study is needed to confirm that 2% urea in the diet would not cause adverse effects on animal health.