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 possibility of using meteorological data obtained from a public meteorology station in determining the effect of air temperature and relative humidity on milk yield in Holstein dairy cattle raised in Diyarbakir province of Türkiye. Records on daily milk yield obtained from a commercial farm were used in the study. Meteorological records including daily maximum and minimum temperatures and daily maximum and minimum humidity data were obtained from the nearest public weather station. A total of 185 healthy Holstein dairy cattle, with five different lactation parities, as well as details on some environmental conditions such as, year, month, lactation period, weather temperature, and the humidity that the animals are exposed to are included in the dataset relating to milk production. Five different temperature-humidity index variants, including THIa (maximum temperature and humidity), THIb (minimum temperature and humidity), THIc (average temperature and humidity), THId (maximum temperature and minimum humidity), and THIe (minimum temperature and maximum humidity), were considered to evaluate the effect of heat stress on milk production. The critical values at which the milk yield began to decrease due to heat stress in this study slightly deviated from the critical value of 72, which is accepted as the threshold value for the start of heat stress and determined as 77, 54, 64, 69, and 54 for THIa, THIb, THIc, THId, and THIe, respectively. Based on these values, the loss of milk production of one cow per year was calculated as 98.25, 157.68, 207.36, 164.30, and 190.08 kg when using THIa, THIb, THIc, THId, and THIe, respectively. This study confirmed that weather stations located away from farms provide useful information for research on heat stress in dairy cows. It can be concluded that THId, which shows the least deviation from the critical value of 72 (only 3 unit), better reflects the stress condition that animals are exposed to due to temperature and humidity. For this reason, the highest daily air temperature and lowest daily humidity appear to be the most important factors in this investigation to assess heat stress and both variables can be combined into a THI.

Keywords

• heat stress
• temperature-humidity index
• milk production loss
• meteorological data