Effect of meteorological parameters above core body temperature of dairy cattle under tropical conditions

Heat stress is one of the major constraints of animal productivity, especially in the tropical belt and arid regions. The aim of this study was to measure the climate vulnerability of a specialized milking system in high land tropics of Colombia classified as a low mountain wet forest ecosystem. Three groups of eight Holstein cows were implanted with an intravaginal device adapted to a data logger thermometer (VEMCO minilog II (R)) for 6 days long and programed to measure corporal temperature. Herd and individual behavior of grazing, rumination, rest and water intake were measured. Meteorological conditions (solar radiation, air temperature, relative humidity, precipitation, wind speed) were measured from July to October with a meteorological station (RAINWISE LR (R)) installed in the grazing area of a 35 group of cattle in first third of lactation. Four different indexes of heat stress were compared (temperature humidity index, equivalent temperature index, equivalent temperature stress index and respiration rate index). Additionally, infrared thermographic photos were taken with a FLIRE50 (R) four times a day at 6, 10, 16 and 20 hours. The surface temperatures of back, belly, face and udder were analyzed with FLIRTOOLS (R). The indexes of heat stress showed low correlation rates with water consumption, milk production and vaginal temperature. The solar radiation was the atmospheric parameter with highest correlation with water consumption (R²=0,24; P<0,005), reaching a mean of 95 liters of water per day. The vaginal temperature (mean 38,6?C, SE + 0,65) showed high correlation rate with behavior (R²=0,36; P<0,005) and superficial temperature of the eye (mean 35,1?C, SD +0,45) and udder (mean 34,8?C; SE + 0,6) (R²=0,38; P<0,005). Current results suggest that tropical conditions need the development of new indexes of thermal stress that include solar radiation and other physiological parameters that could be measured by non-invasive methods.