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¹ Samsun Yem Sanayii Ticaret A.Ş, Samsun, Türkiye
² Ondokuz Mayıs Üniversitesi Veteriner Fakültesi Zootekni Anabilim Dalı, Samsun, Türkiye - Effect of temperature-humidity index levels on production traits in dairy cattle about to information were reviewed. Climatic conditions influence on the welfare and production performance of livestock. Current climate models predict the increase in global avarage surface temperature within the next 100 years may be between 1.8°C and 4.0°C due to the deterioration of the global atmospheric composition. Relative humidity affects feeling degree of ambient temperature. The common effect of ambient temperature and relative humidity is expressed in a single value which called `temperature-humidity index (THI)` on production traits in livestock. Milk production is not affected by heat stress when mean THI values are equal to 71 or below 71, production loss is moderately affected when at THI of 71-79, production performance is severely affected when THI value is above 80. It was reported that reproductive and milk yield traits generally decreased in summer season in dairy cattle. However, it was reported that Holstein cows were more susceptible versus heat stress than that of Jersey, Esmer and Simmental. Also, it was reported that daily milk yield decreased approximately 0.9-2.2 kg due to heat stres in summer season. Furthermore, it was determined that average changes per increase of 1 THI unit of range 180-360 g of daily milk porduction in dairy cattle. Keywords : Dairy cattle, heat stress, milk yield, fertility