Effects of air temperature and relative humidity on milk yield of Holstein dairy cattle raised in hot-dry Southeastern Anatolia Region of Türkiye

Abstract

The aim of this study is to investigate the possibilities of using the meteorological data obtained from the public meteorology station in determining the effect of air temperature and relative humidity on milk yield in Black and White dairy cattle raised in Diyarbakır province of Turkey. Records on daily milk yield obtained from a commercial farm in Diyarbakır province were used in the study. Meteorological records containing daily maximum and minimum temperature and daily maximum and minimum humidity data were obtained from nearest public weather station in Diyarbakır province. Data set related to milk yields includes 46 438 daily records during five different lactations of 185 healthy Black and White dairy cattle and information of some environmental factors of the animals. In the study, five different temperature-humidity index (THI) types consisting of different combinations of daily maximum, minimum and average temperature and humidity values were considered to evaluate the effect of heat stress on milk production. This study confirmed that weather stations located away from the farms contain useful information for research on heat stress in dairy cows. Using the combination of maximum daily air temperature and minimum daily humidity in THI formula performed better than other THI types in quantifying the heat stress in this study. This combination was less affected by other environmental factors and the results obtained from this combination seems to be more biologically meaningful. According to this, dairy cattle were exposed to heat stress for 160 days between May and October in a year. In this period, the losses of milk production were 1518.85 and 0.73 kg for per cow per year and per unit THI increase, respectively.