Abstract: 【Objective】Effect of heat stress on dairy goat production performance and rumen epithelial cell morphology were studied in order to provide a rational and experimental basis for animals in hot environments to maintain normal physiological function and to explore methods of resistance to heat stress. 【Method】 The animal modes were estabished when temperature and humidity index ＞72 (THI＞72) of early, medium and evening for a week. The effect of heat stress on rumen fermentation pattern, digestion and metabolism of nutritive materials, performance, morphology and structure of rumen epithelial cell were studied with mid- and late-lactation dairy goats by animal nutrition methods in this project. 【Result】 The results showed that THI of test sheep was between 72 and 87 during the tests, and in the mild and high heat stress, which showed dairy goat in continuous heat stress state during the whole experiment period. Heat stress significantly increased rectal temperature and respiration rate (P＜0.01), significantly reduced DM, CP, OM, NDF and ADF digestibility (P＜0.01), dry matter intake and milk yield of dairy goats (P＜0.01 ), and significantly reduced dairy goat milk protein and milk fat content (P＜0.05), but the effect on lactose content was not significant (P＞0.05). Heat stress significantly decreased pH value, NH3-N concentration and TVFAs concentration (P＜0.05) at each time point in a day. Compared with the control group, rumen fluid of dairy goat was found gruel shape and strongly sour flavor, and the rumen mucosa nipples showed a wide range of necrotic and fall off when in heat stress for 30 days, and the situations of mucosa papillary necrosis and fall off were more serious when in heat stress for 45 days. This showed that heat stress caused a certain degree injury to the animal rumen mucosa. In the heat stress for 30 days and 45 days, the length and width of rumen dorsal sac and ventral sacs villus were shorter than that of control group (P＜0.05), and with the prolonged heat stress, the length and width of rumen dorsal sac and ventral sac villus were shortened more short (P＜0.05). 【Conclusion】Heat stress can significantly improve rectal temperature and respiration rate, significantly reduce dietary nutrient digestibility, rumen fermentation parameters, dry matter intake, milk quality and performance of the dairy goat. Heat stress can damage morphology of rumen epithelial cell, make the mucosal villi atrophy, shed and even necrosis, which increase permeability of the rumen epithelial cell.

Key words: heat stress , dairy goats , production performance , rumen epithelial cell , morphology