Investigation Of Heat Stress And Summer Cooling Models Of Dairy Cows In Shanghai Area

Dairy cows were very sensitive to heat stress. Milk yield would drop at20℃. The milk production was decreased nearly50%if the temperature was over28℃. Shanghai had a subtropical humid monsoon climate. July was usually the hottest and the maximum temperature was about35℃to38℃. This study aimed to investigate the climate in Shanghai and the summer cooling model in large-scale dairy farm. The impact of heat stress on dairy production performance and raw milk composition were also investigated. The study also reported some physiological changes when the cows were under heat stress. The research contains three parts:Part1The investigation of climate and environment and summer cooling mode in Shanghai.42scaled dairy farms were selected from116dairy farms in Shanghai area. The climate and summer cooling mode was investigated. The results showed that the annual heat stress period for cows were from May to September. The annual average relative humidity was over70%. The average monthly wind speed was10-12km/h. THI index was above70. The critical temperature of heat stress in the region was between23℃to25℃. Nearly90%of the farm used the natural ventilation mode,10%of the dairy farms used tunnel ventilation. But none used low roof ventilation mode.Part2The impact of heat stress on production performance of lactating dairy cows in Shanghai.6000dairy cows were studied in several state-run dairy farms. The results showed that milk fat rate and milk protein rate of raw milk was significantly decreased (p<0.01). The number of bacteria was significant increased (p<0.01). Somatic cell count(SCC) was also significantly increased (p<0.01) in June, July, August and September. Total number of abortions were significant increased (p<0.01) from July to September. Puberty pregnancy rate was significantly lower (p<0.01) in July, August and September. The number of death was higher than other months from July to September. The digestive system, lactation system and reproduction system had no significant difference. But limb hoof diseases increased apparently in June, July, August and September.Part3Different summer cooling mode effects on physiological indicators of cows. Test by cows shed which take three summers cooling mode, each cows shed were collected six corresponding points, respectively. A total of54Holstein cows were used to determine cow’s breathe, heartbeat and rectal temperature of experimental group. The results show that the experimental group of3has about45.4times/min in respiratory rate. It was relative decline of15.8%than the test group of1which has53.9beats/min(P<0.01); and it was relative decline of11.8%than the test group of2which has51.5beats/min (P<0.05). The heart rate of the test3was about76.7beats/min, it was relative decline of9.44%than the test1which has84.7beats/min(P<0.07); and has7.5%than the test2which has82.9beats/min(P<0.01). The average rectal temperature of experimental group3was about38.6℃, it was relative decline0.5%than the test3which has38.7℃(P<0.05); and has0.4%than the test2which has38.6℃. In addition, the correlation coefficient of ETI with the respiration rate, heart rate of cows was0.918,0.921, and the level related up to significantly (P<0.05).