Effects of Heat Stress on Feed Intake, Nutrient Digestibility and Production Performance of Dairy Cows

This experiment was conducted to investigate the effects of heat stress on feed intake,nutrient digestibility,and production performance of dairy cows during different lactating periods.A 2 × 3 crossover design was used and eighteen healthy Chinese Holstein cows after calving at 2-3 parity were selected.The cows were allocated into three treatments based on their milk yield,parity and lactating days: early lactation treatment(15 ～100 d),mid-lactation treatment(112～175 d) and late lactation treatment(200 ～230 d),six cows in each treatment.Self-control trial between heat stress period and non-heat stress period were used based on THI measurement on site.Results showed that the feed intake of dairy cows decreased significantly in middle and late stage of heat stress(P 0.01);the nutrient digestibility of DM,CP,EE,NDF,ADF,Ca and P during heat stress period were lower than those during non-heat stress period significantly(P0.05);the milk yield during middle heat stress period decreased significantly(P0.01);there were no significant difference in milk composition except milk protein and non-fat solid during early lactation increased with the prolong of heat stress(P 0.05);there was no significant difference in feed intake,nutrient digestibility and milk composition during different lactation stage in the same heat stress period..In conclusions,heat stress resulted in the feed intake,nutrient digestibility and milk yield of dairy cows decreased,while the milk yield during different lactation stage in the same heat stress period decreased significantly with the prolong of lactation(P0.01)