Behavioral and physiological responses to an inspired-air supplemental cooling system for dairy cows in free-stall housing.

Abstract

During heat stress, dairy cows spend less time lying down to dissipate heat. Heat stress abatement strategies generally target cows outside of their resting areas. However, cooling cows while in their stalls could help alleviate heat stress without compromising lying behavior. The objective of this study was to assess the effects of an inspired-air supplemental cooling system (SCS) on respiration rate, rectal temperatures, lying behavior, rumination time, and milk production (energy-corrected milk, ECM) of lactating dairy cows. A free-stall pen was retrofitted with custom stall partitions to deliver cooled air and mist. The pen, including the stall platform, was divided into two separate sides. Twenty-eight lactating Holstein cows were randomly sorted into two groups, each housed on one side of the experimental pen. Cows experienced four treatments (control, CTRL; cooled air, AIR; mist, MIST; cooled air and mist, AIR+MIST) in a four-treatment, four-period, two-sequence crossover design, with each period lasting seven days. Cooled air was provided continuously, and mist was cycled 3min on, 12min off from 0900 to 2100h. Respiration rates were observed hourly between 0900 and 1500h, and only measurements recorded while cows were lying down were used in the analysis. Rectal temperatures of 16 focal cows were recorded at 1545h once per day. Lying behavior and rumination were recorded continuously, and milk yields recorded twice daily were used to calculate ECM. Throughout the experimental period, the average temperature-humidity index was 66.4±6.07. During the MIST treatment, the respiration rate was lower than the CTRL (45.7 vs 49.0±1.92 breaths/min) and AIR (45.7 vs 48.7±1.92 breaths/min). CTRL and AIR did not differ (48.7 vs 49.0±1.92 breaths/min), and MIST and AIR+MIST (45.7 vs 47.1±1.92 breaths/min) did not differ. All other variables were not significantly different between treatments. In conclusion, the SCS appeared to be tolerated by cows and shows the potential to assist in alleviating heat stress. The cooling capacity needs to be evaluated under more extreme environmental conditions causing heat stress than those experienced during this study. Further testing is required to determine the cooled air temperature specifications and mist delivery frequency.