Effect of Heat Stress on physiological, behavioural, and production responses in lactating dairy cows

Heat stress is one of the most significant issues occurred in the dairy systems during the last decades with adverse consequences on welfare and production. This study aims to evaluate the effect of heat stress on the main major physiological, behavioural and productive parameters considering two dairy herds located in hill/mountain area. Twenty Friesian cows were checked in two climatic condition periods: no stress, with average diurnal THI < 72 and heat stress with THI > 72. Physiological indices (respiration rate, panting score, skin udder temperature, heat evaporation loss, and heat stress index) as well as milk yield, were during 5 trial consecutive days for each period. Animal behaviours were recorded from 9 a.m. to 4 p.m., including feeding, dynamic and grooming activities. In the heat stress period, cows presented higher values relative to physiological parameters. In addition, the cows decreased the feeding frequency (from 25.18 to 14.74%) increasing their standing (from 9.73 to 22%) and drinking (from 1.77 to 3.60%) behaviour. Milk yield decreased (-3kg/day/cow), as the climatic conditions worsened. The results of this study confirmed the need of more effective strategies development to mitigate the heat load in dairy cattle also in hill/mountain area.