Research Of Extreme Temperatures On The Production Performances And Physiological Conditions Of Holstein Dairy Cows And Regulations

After20years of rapid development for the dairy cow industry, scale level of the dairy farm and milk yield were increased greatly. However, the dairy industry has been troubled by the heat and cold stress, particularly the impact of severe heat stress in summer. Some of the superiority producing areas of raw milk in China was affected by the extreme cold during winter, which has not yet got enough attention. Thus research on the physiology and production performance response mechanism of dairy cows under cold stress and to alleviate cold and heat stress were important. More works were needed to do to improve the thermal comfort of the dairy cows.The research focused on the analysis of cold and heat stress situation in China. This will help to improve the design and the environmental control of dairy barns. A lot of thermal indexes and a heat dissipation of dairy cows in different environment were reviewed. The following conclusions were obtained:1. The cold stress of northeast of China, includes Heilongjiang, Jilin, part of Inner Mongolia and Shanxi was severe with extreme low temperature. Another part of the region in northern Xinjiang and Gansu also surfer low temperature in winter. More attention should be given in practical management The thermal insulation of dairy housing in these areas should be improved, and the main object of the environmental regulation was to preserve heat loss. The analysis of THI showed that the entire Southern, Eastern, Midwestern and Northern China undergo severe heat stress during the summer, which is relatively mild in Northwest and Northeast. The relative humidity differed a lot between different regions. Then the environmental control measures in alleviating heat stress need to consider their own characteristics. Specific technique was needed to fit the particular areas.2. In this study, water temperature of the sprinkler system is reduced by about2.8℃by the insulation of water tank. The cooling effect was better for the sprinkler syetem with a spray interval of4min. Blood biochemical parameters results indicated that the decreased water temperature could improve the cooling effect by reducing the loss of sodium and potassium ions in dairy cows. The skin temperatures of cows with spraying time of45s and60s were0.3-1.2℃lower compared with the spraying time of30s under moderate heat stress. Considering the problem of waste water, spraying time of45s is recommended in practical use.3. The production performance of dairy cows in different levels was affected by the fluctuations or sharp decrease of air temperature. The regression analysis showd that the high and low-yield dairy cows were much more susceptible to temperature fluctuations than the mid-yield dairy cow. So more attention should be given to the environmental control of high-yielding dairy cows in order to maitain its higher productivity.4. Milk yield increased19.4-32.4%in the barn with the air temperature above0℃, which could achive by using better thermal insulation materials. This further validates the hazards of cold stress on dairy cows, and also the importance of improve the thermal insulation of dairy barns in cold areas.