The effect of temperature and relative humidity on milk yield of holstein dairy cattle raised in agricultural enterprises under different climatic conditions

This study was conducted to investigate the effect of air temperature and relative humidity on milk yield of the Holstein dairy cattle raised in Agricultural Enterprises under different climatic conditions in Turkey (Polatlı, Türkgeldi, and Çukurova) and to examine the differences between the enterprises. Records of milk yield on the test day for the years 2014-2020 obtained from the General Directorate of Agricultural Enterprises (TİGEM) were utilised in the study. The data set related to milk yields included the number of Holstein cows, data on different lactation orders, control records of milk yield and information of the animals for some environmental factors. In the study, values of four temperature-humidity indices (THI) consisting of different combinations of daily maximum and minimum temperature and humidity values were examined in order to assess the effect of temperature stress on milk yield. Consequently, the difference between the enterprises in terms of the combinations of the temperature-humidity index was found to be statistically significant (P<0.05). The THI value calculated for the agricultural enterprises varied between 10 and 102. It was determined that dairy cattle were exposed to heat stress between May and November in Türkgeldi and Polatlı Agricultural Enterprises in the cold climate zone and between April and July in Çukurova Agricultural Enterprises in the temperate climate zone. While the THI value with low humidity weight was the optimal indicator in a humid climate, the THI value with high-temperature weight was the best indicator of heat stress in a semi-arid climate.