Effects of air temperature and humidity on average daily gain in feedlot cattle of different genotypes

The purpose of this study was to observe Holstein, Brown Swiss, Simmental and cross breed Anatolian Black genotypes fattened in feedlot regarding their ability to tolerate temperature and humidity and to compare Temperature Humidity Index types under climatic conditions of Şanliurfa province in Turkey. Data obtained from a commercial farm composed of 70 594 test day records of 11 117 cattle (6 513 Holstein, 3 546 Brown Swiss, 838 Simmental and 220 Anatolian Black Crosses). Meteorological data were provided from nearest weather station located 9.04 km away from feedlot area. THI values were calculated by using daily maximum, minimum and average air temperature and, humidity values according to three different combinations for each animal. Analysis were based on such a model that includes effects of year, sex, age, season, days on feed, beginning stage of fattening and several types of THI. Results showed that, Simmental and Anatolian Black genotypes were slightly more tolerant to heat stress compared to Holstein and Brown Swiss. In addition, Anatolian Black genotype was more sensitive to cold stress when compared to other genotypes. Different breakpoint values for stress and comfort zone intervals were obtained when different combinations of temperature and humidity variable (maximum or minimum) were used in THI formula. After 72 THI values, which is reported in literature as the threshold for heat stress in cattle, average daily gain loses were observed. But, this is only detected when maximum temperature and minimum humidity variable is used. Results from this study indicated that trends of temperature and humidity in the air were important factors for THI calculation types when data from the weather stations were used. Because, this gives useful information about, which combination of temperature and humidity values (maximum, minimum or average) best reflect the heat stress for genotype.