Effective Heat Stress Mitigation Through Benchmarking in Dairy Farms

Thermal stress in dairy cattle poses a major threat to the dairy industry’s viability. Multiple studies have documented the negative impacts of thermal stress on cattle well-being and productivity. Cattle experiencing thermal stress show reduced feed intake (West, 2003; Spiers et al., 2004; Baumgard and Rhoads, 2013), milk production (Collier et al., 1981; Gantner et al., 2017; Tao et al., 2020), and fertility (García-Ispierto et al., 2007; Morton et al., 2007; Schüller et al., 2014).

In severe cases, extreme thermal stress can lead to cattle death. The estimated economic impact of thermal stress on the U.S. dairy industry ranges from $897 million to $1.5 billion annually (St-Pierre et al., 2003) just for lactating cows and young cattle.

These estimates are now outdated. With the 10 warmest years recorded between 2014 and 2023 (NOAA National Centers for Environmental Information, 2024), the current economic impact is likely higher and will continue to rise as global temperatures increase. Recent studies also suggest an additional $1.4 billion in costs due to the long-term effects of thermal stress on dry cows (Laporta et al., 2020).

During periods of heat stress, cows tend to stand more, reducing their resting time (Cook et al., 2007; Allen et al., 2015; Ortiz et al., 2015). As the temperature-humidity index (THI) rises, resting times have been seen to decrease by up to 3.3 hours per day, due to shorter duration of each rest period (Nordlund et al., 2019).

During a single rest period, cows can experience a rise of 0.40 to 0.48 °C in central body temperature, while they can lose heat at a rate of up to -0.25 °C per hour when standing (Nordlund et al., 2019). Cows are highly motivated to lie down (reviewed by Tucker et al., 2021), and can become frustrated and uncomfortable when the need to lie down conflicts with the need to dissipate heat (Polsky and von Keyserlingk, 2017).

Moreover, extended periods of standing under thermal stress might explain both the increased rates of hoof injuries observed at the end of summer (Cook and Nordlund, 2009) and the higher prevalence of lameness towards the end of summer and fall (Cook et al., 2006; Sanders et al., 2009). These cumulative and delayed effects of heat stress on lameness risk are not accounted for in current economic estimates.

Approximately 98.7% of U.S. farms use at least one form of heat mitigation, such as shade, fans, or sprinklers to alleviate the detrimental effects of heat stress on well-being and productivity (USDA, 2021).

Studies using water-based cooling methods, such as sprinklers or misters, have shown reductions in physiological responses like respiratory rate (Correa-Calderon et al., 2004; Schütz et al., 2011) and vaginal temperature (Kendall et al., 2007; Chen et al., 2016), along with increases in milk production (Flamenbaum et al., 1986; Chen et al., 2016) and dry matter intake (Strickland et al., 1989; Levit et al., 2021). However, these methods do not fully restore reduced resting times during heat stress (Overton et al., 2002; Legrand et al., 2011; Chen et al., 2013). They found that fans providing air speeds of at least 1 m/s at the cow’s resting height (0.5 m above the bed surface) increased daily resting times by an average of 1 hour per day compared to facilities where cows only had prevailing winds and shade (Reuscher et al., 2023). Properly calibrated fans also kept vaginal temperatures within the normal physiological range (≤39.2 °C; Merck Veterinary Manual, 2012), whereas without fans, temperatures reached up to 40.1 °C on the hottest days (Reuscher et al., 2023). These fans were also effective in reducing respiration rates and improving milk production and dry matter intake (Reuscher et al., 2023). These findings align with the recommended minimum cooling air speed (MCAS) of ≥1 m/s at the cow’s resting height to maintain a favorable heat loss gradient around resting cows (Mondaca, 2019). Providing specific facility data in a benchmarking report can support management decisions to enhance the MCAS at the cow’s resting height on farms. Benchmarking is a valuable tool for comparing one’s performance with others and identifying areas for improvement (Anand and Kodali, 2008).

Research shows that providing benchmarking reports to dairy farms leads to changes that improve outcomes such as calf growth and passive immunity transfer (Atkinson et al., 2017) or lameness rates in cows (Chapinal et al., 2014). Reports identifying areas for improvement and suggesting solutions can empower farmers to make informed decisions on specific issues (Sumner et al., 2018).

The research team previously developed a standardized method for reporting ventilation performance in dairy facilities with free stalls, both mechanical (e.g., cross-ventilation) and natural ventilation (Mondaca et al., 2019). This method measured air speeds at cow standing and resting heights (1.5 m and 0.5 m, respectively) for 3 minutes per location, along with barn temperature and relative humidity.

The goal of this study was to assess the performance of summer ventilation systems in a sample of Wisconsin dairy facilities with natural and mechanical cross-ventilation and refine the evaluation method for industry application. They hypothesized that facilities with consistently higher air speeds at the cow’s resting height (0.5 m) would offer the most effective heat reduction. Specifically, they predicted that cows in facilities with higher air speeds would have longer daily resting times (fewer daily rest periods but longer duration per period) and a lower maximum daily vaginal temperature.

Source: Reuscher, K. J., Cook, N. B., Halbach, C. E., Mondaca, M. R., & Van Os, J. M. C. (2024). Consistent stall air speeds in commercial dairy farms are associated with less variability in cow lying times. Frontiers in Animal Science, 5. https://doi.org/10.3389/fanim.2024.1422937