Impacts of Heat Stress on Cow and Calf
Heat stress has negative impacts on dairy cattle at different stages of their life cycle. Compared with the lactating dairy cow, the dry cow and neonatal calf have lower upper critical temperature but their performance is still negatively impacted by heat stress. During the dry period, heat stress elevates cow body temperature and also disrupts several normal physiological functions during late gestation, such as impaired mammary growth and fetal development, which compromise future performance of the cow and calf. Compared with cooled cows, heat-stressed dry cows have lower milk production in the subsequent lactation and altered metabolic and immune function during the transition period. Maternal heat stress of dams during the dry period also has negative effects on their offspring. For example, calves born to heat-stressed cows have lower birth weight and impaired ability to absorb immunoglobulin from the colostrum relative to calves from cooled dams. Emerging evidence also suggests that heat stress in utero may have long-term impacts on a heifer’s future performance, including milk production in the first lactation. Heat stress has direct negative impacts on neonatal calf performance as well. When exposed to heat stress, calves have impaired passive immunity and high mortality rate in the first month of life. Additionally, heat stress lowers a calf’s average daily gain, feed efficiency and overall growth during early life. Thus, proper management tools need to be implemented to cool the dry cow and neonatal calf as a way to alleviate the negative impacts of heat stress on these animals.
Keywords: heat stress, dry period, dairy calves