Sophisticated Model Developed by Research Team to Evaluate Heat Stress in Lactating Cows

University of Minnesota researchers have developed a highly sophisticated model for assessing the heat stress of a lactating cow, a problem that can lead to several health complications for cows and financial hardship for dairy producers due to lower milk yields and pregnancy rates.

Although many empirical equations have been developed to determine heat stress conditions, the new model is the most comprehensive available. It was recently detailed in two papers in Journal of the American Society of Agricultural and Biological EngineersThe first paper describes the equations and cow characteristics used in the modified model, and the second paper compares model results with data from heat-stressed cows and unpublished data from solar panel shade work done at West Central Research and Outreach Center in Morris, Minnesota.

The research team modified the stable heat transfer model developed by McGovern and Bruce (2000) by integrating the work of two other researchers, two new empirical relationships for bovine properties, and performing a new solution.

The modified model describes the heat exchange between the lactating cow and the environment through respiration, airflow through the cow, perspiration, shortwave, and longwave radiation. The model can be used to evaluate the effect of body mass, milk production, solar load, air temperature, dew point temperature, and air velocity on heat exchange rates, cow respiration rate, and body temperature.

Researchers found:

• Results from the process-based model compare well with published respiration rates and body temperatures of heat-stressed lactating cows.
• Model results were generally within one standard deviation of the reported means.
• The thermal equilibrium model can be used to identify key heat stress factors and to evaluate mitigation practices.

“Process-based models provide a better understanding of how cows exchange heat with the environment than empirical equations. Engineers will be able to use the model to better evaluate alternative cooling designs,” said Kevin Janney, a professor in the Department of Biological Products and Biosystems. Engineering and ancillary engineer.

Creating better cooling designs can help reduce health conditions associated with heat stress, which include decreased milk production and pregnancy rates, increased morbidity and mortality rates, lower birth weight calves, and poor immune function.

Looking into the future, the researchers plan to use the modified model to evaluate alternative cow cooling designs and the trade-off associated with the costs of ventilation fans, cooling fans, and evaporative cooling systems versus reduced heat stress on lactating cows.