Recently, the climate has shown a significant shift toward warmer conditions, further compounding the existing challenges of managing heat stress for dairy operations and cattle health in those systems. Mature, lactating dairy cattle are highly susceptible to heat stress due to the energy required for lactation, metabolic heat produced by the animal, and limitations for heat dissipation. The consequences of heat stress are often associated with reduced milk yield, negative reproductive impacts, and elevated disease rates which may create unfavorable economic conditions and animal welfare concerns. Significant opportunities for research and the development of mitigation strategies to tackle the short- and long-term effects of heat stress exist.
Heat stress occurs when the core body temperature of the animal increases beyond the normal physiological range and the animal diverts energy from other biological processes and modifies behavior to find cooler spaces. These modifications may impact productivity, health, and reproduction, which are critical aspects for the sustainability of the dairy operation. Heat stress varies in severity depending on the environmental conditions contributed to by factors not simply limited to temperature. Humidity, wind speed, precipitation, solar radiation, farm microclimate, regional variability, and access to shade are other such examples of environmental factors that influence the animal’s core body temperature. Further, animal factors that are understood to influence heat stress susceptibility are production status, concurrent disease, and hydration status.
Due to the economic importance of the lactating dairy cow in the dairy industry, most applicable research on heat stress in dairy systems prioritizes understanding the physiological responses of the lactating dairy cow. Currently, there is limited research in the context of heat stress during the early life stages of dairy calves. The short-term consequences of heat stress in calves are often associated with elevated disease rates, mortality, and reduced growth and development. The long-term consequences of heat stress on calves need further research to better understand how intensity, frequency, and duration of heat stress events impact calf development.
In an upcoming study, AgNext researchers will evaluate the physiological response to heat stress at the molecular level in dairy heifer calves. Using laboratory analysis techniques, we will identify candidate genes by analyzing the proteins found in plasma that improve the animal’s ability to mitigate heat stress. The identification of these genes and proteins will allow researchers to identify markers of heat stress resiliency and if successful, could be used as a tool for herd selection programs aimed at developing more heat-tolerant dairy herds.
Through the utilization of a weather station that monitors and records an array of weather patterns at the study site, researchers hope that the conditions that produce heat stress in dairy calves can be more precisely defined. Through a more precise definition of the environmental factors that lead to calves experiencing heat stress, dairy producers gain an improved ability to make housing management decisions to mitigate the effects of calf heat stress. In addition, clinical health and behavior measurements of dairy calves will be utilized to determine the housing and bedding options that maximize calf health during heat stress conditions. The research will also provide preliminary insight into the long-term consequences of heat stress during calfhood by studying protein expression and making the relevant connections to gene expression in the pre-weaned dairy heifer. This study will be important in laying the foundation for future calf heat stress mitigation research which is an opportunity to improve the overall sustainability of the dairy industry.

Amanda Houghton
Combined Master’s and D.V.M. Student