Effects of heat stress on milk production and its composition in holstein breed reared in Siirt conditions

This study aims to investigate the effect of heat stress on body temperature, milk yield, and milk composition in dairy cattle. For this purpose, rectal temperature, milk yield, and composition values were obtained monthly in Ceylanlar Agricultural Farm, located in Yunuslar village of Kurtalan district of Siirt province. Values related to these parameters were recorded in March, April, May, June, July, August, and September. In addition, temperature and humidity values are recorded in the farm conditions and used to calculate the temperature-humidity index values that were used to calculate the heat stress. SAS 9.4 software was used for statistical analysis of the data. Proc Means, Proc Corr, and Proc Mixed commands were applied in the analysis. Relations between variables in the continuous structure used in the study are calculated using Pearson correlation coefficients. In the findings of this study, a significant positive correlation between heat stress and body temperature (p<0.001), and a significant negative correlation between heat stress and milk yield (p<0.05), and between heat stress and milk fat ratio (p<0.01) were observed. Although there was a negative correlation between heat stress and milk protein, lactose, and dry matter ratios, this relationship was not statistically significant. As a result, it was determined that the heat stress started from the middle of May to the end of September on the farm the work was carried out. Accordingly, it has been determined that the heat stress that occurs during summer in the study region affects the body temperature, milk yield, and milk fat ratio negatively in dairy cattle.