Abstract: 【Objective】 This study aimed to investigate the effects of curcumin (CUR) on growth performance,apparent digestibility of nutrients and serum biochemical indexes of breeding cattle under heat stress condition,and to explore the appropriate curcumin supplementation level in beef cattle diets under heat stress condition. 【Method】 Thirty-two healthy Yanbian Yellow breeding cattle,weighing 286.36 kg±3.95 kg,were randomly divided into four groups,with eight replicates in each group and one cow in each replicate.The curcumin supplemental levels for each group were set at 0,100,200 and 300 mg/kg DM diet respectively，named as control group,100 CUR,200 CUR,and 300 CUR groups.The prefeeding period was 7 days and the test period was 30 days.During the experiment,the temperature and relative humidity of the cowshed were measured at different time points every day,and the temperature and humidity index (THI) was calculated.During experimental period, THI≥72,the experimental cattle were considered to be in a state of heat stress.On the morning of the 31st day,the experimental cattle were weighed and their body size was assessed.Blood was drawn from the jugular vein to test serum biochemical indicators.The total fecal collection method was used to collect fresh feces for the measurement of apparent digestibility of feed nutrients. 【Result】 Compared to control group,cattle in 200 CUR group exhibited significant improvements in average daily weight gain,body depth,and chest circumference (P＜0.05),alongside a notable reduction in feed-to-gain ratio (P＜0.05).The apparent digestibility of crude fat,neutral detergent fiber and acid detergent fiber were significantly enhanced (P＜0.05),serum albumin and thyroid hormone levels were markedly elevated (P＜0.05),whereas activities of glutamate-oxaloacetic transaminase and glutamate-pyruvic transaminase as well as triglyceride content were significantly diminished (P＜0.05),furthermore,malondialdehyde levels showed a significant decrease (P＜0.05) in 200 CUR group.Compared to control group,the body height,crude protein digestibility,serum total protein and globulin contents were significantly increased (P＜0.05),the levels of heat shock protein 70 and cortisol were significantly decreased (P＜0.05) in three experimental groups.Serum immunoglobulin A was significantly increased in 100 CUR group (P＜0.05).The activities of superoxide dismutase,glutathione peroxidase,and total antioxidant capacity in bovine serum were significantly elevated in 200 CUR and 300 CUR groups (P＜0.05). 【Conclusion】 Adding 200 mg/kg DM curcumin to the diet of Yanbian Yellow breeding cattle during heat stress could improve their growth performance,apparent digestibility of feed nutrients,and antioxidant capacity.

Key words: curcumin; Yanbian Yellow cattle; blood index; growth performance; heat stress