Guanidinoacetic acid supplementation improves intestinal morphology, mucosal barrier function of broilers subjected to chronic heat stress

The current study is designed to investigate dietary guanidinoacetic acid (GAA) supplementation on the growth performance, intestinal histomorphology, and jejunum mucosal barrier function of broilers that are subjected to chronic heat stress (HS). A total of 192 male broilers (28-d old) were randomly allocated to four groups. A chronic HS model (at a temperature of 32 °C and 50%-60% relative humidity for 24 h daily) was applied in the experiment. Normal control (NC, ad libitum feeding, 22 °C), HS group (HS, ad libitum feeding, 32 °C), pair-fed group (PF, received food equivalent to that consumed by the HS group on the previous day, 22 °C), guanidinoacetic acid group (HG, ad libitum feeding, supplementing the basal diet with 0.6 g/kg GAA, 32 °C). The experiment lasted from 28 to 35 and 28 to 42 d of age of broilers. Our results showed that broilers subjected to HS had lower average daily feed intake and average daily gain (P < 0.05), higher feed-to-gain ratio and relative length of the small intestine (P < 0.05), as well as lower relative weight and weight per unit length of the small intestine (P < 0.05). HS damaged the small intestinal histomorphology by decreasing the small intestinal VH and the VH/CD (P < 0.05). Compared with the HS group, supplementation with 0.6 g/kg GAA increased jejunal VH and VH/CD (P < 0.05), but decreased relative weight and relative length of the small intestine (P < 0.05). Moreover, in comparison with NC, HS elevated intestinal permeability (D-Lactic acid concentration and diamine oxidase activity) and mRNA expression levels of interleukin-1β, interleukin-6, and tumor necrosis factor-α (P < 0.05), reduced jejunal mucus thickness, number of goblet cells, IgA + cell density, and mucin2 mRNA expression level of broilers (P < 0.05). Compared with the HS group, dietary GAA elevated jejunal mucus thickness, goblet cell number and IgA+ cell density (P < 0.05), and up-regulated jejunal mRNA expression of interleukin-1β and tumor necrosis factor-α (P < 0.05). In conclusion, HS impaired growth performance, and the intestinal mucosal barrier function of broilers. Dietary supplementation with 0.6 g/kg GAA alleviated HS-induced histomorphology changes of small intestine and jejunal mucosal barrier dysfunction.With the global warming getting worse, heat stress (HS) has been a serious problem faced by poultry industry. As one of the main target organs, the intestine is easily affected by HS. Broilers are particularly sensitive to hot temperatures, and HS occurs when temperatures rise above the optimum (16–26 °C). Moreover, ambient humidity below 40% and above 80% also affects broilers adversely. HS can impair intestinal morphology and function of the intestinal barrier. The intestinal mucosal barrier not only plays key roles in nutrient digestion and absorption but also serves as the innate defense barrier fending off noxious substances within the intestinal luminal environment. Therefore, protecting intestinal mucosal barrier from HS is important to animal health. Nutrient regulation is an economical and effective method to alleviate HS of intensively-farmed broiler chickens. The results of current study demonstrated that chronic HS impaired the growth performance and intestinal mucosal barrier function of broilers, while dietary supplementation with 0.6 g/kg guanidinoacetic acid improved intestinal histomorphology and alleviated intestinal barrier dysfunction of broilers subjected to chronic HS, which is beneficial for improving health of broilers.