Review on performance responses of dairy cattle against thermal stress

This manuscript is aimed at reviewing the performance responses of dairy cattle against thermal stress resulting from climate change.  Climate change is the major factor that largely affects the dairy industry. Thermal stress (TS) is the perceived discomfort and  physiological strains associated with exposure to excessive ambient temperature. Temperature and Humidity Index (THI) have been  adopted to describe thermal conditions that drive thermal stress in dairy cattle. The effects of TS are devastating in the dairy industry if  not managed well. The thermo-neutral zone for dairy cattle and calves in the tropics is THI <72. Milk yield reductions of up to 50% have  been reported for Holstein cows due to thermal stress under summer climate conditions. Moreover, thermal stress is associated with  alterations in milk composition. TS reduces the length and intensity of estrus manifestation. Moreover, 80% of estrus may be unnoticeable during the summer season in temperate regions, which further reduces fertility. Conception rates of dairy cows may drop  up to 20–27% in the summer season. Climate-induced thermal stress resulted in a decrease of 3.5 kg and 25 kg in the birth weight and  weaning weight of Fogera calves, respectively. Dry matter feed intake was reduced by 9.6%. Commonly used thermal stress reduction  strategies included modification of the physical environment, breeding for heat-tolerant dairy cattle, and nutritional management. The  productive and reproductive traits are susceptible to the negative impacts of thermal stress with an increase in THI above 68.0 for  Holstein Frisian cattle and their crosses and 72 for tropical cattle under an open shed system. Mitigations of thermal stress by breeding  heat-tolerant animals, using a loose house system, and season-based feeding should be considered an integral component of the dairy  cattle management system.