Projected heat stress challenges and abatement opportunities for U.S. milk production

Authors: Gunn, Kpoti; Holly, Michael; Veith, Tameria - Tamie; Buda, Anthony; PRASAD, RISHI - University Of Auburn; Rotz, Clarence - Al; Soder, Kathy; STONER, ANNE - Texas Tech University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2019
Publication Date: 3/28/2019
Citation: Gunn, K.M., Holly, M.A., Veith, T.L., Buda, A.R., Prasad, R., Rotz, C.A., Soder, K.J., Stoner, A. 2019. Projected heat stress challenges and abatement opportunities for U.S. milk production. PLoS One. 14(3):1-21. https://doi.org/10.1371/journal.pone.0214665.
DOI: https://doi.org/10.1371/journal.pone.0214665

Interpretive Summary: Increases in temperature and humidity with climate change are expected to enhance the risk of heat stress in dairy cows that are raised in confinement. In this study, we used a temperature humidity index to assess the potential impacts of dairy heat stress on milk production in nine regions of the U.S. during the early, middle, and latter portions of the twenty-first century. We also used cost-benefit analysis over the same time frame to evaluate the efficacy of adopting four increasingly intense levels of heat abatement for confined dairy operations: minimal (open barn), moderate (forced ventilation), high (fans and misting), and intense (air conditioning). Results showed dairy heat stress was expected to increase in all regions through the end of the twenty-first century, with the most acute effects seen in southern regions of the U.S. where high to potentially intense levels of heat abatement may be the most cost-effective strategies. Findings from the study demonstrate the importance of assessing possible adaptations to dairy heat stress in the context of climate change and agricultural sustainability.

Technical Abstract: Cost-effective heat mitigation strategies are imperative to maintain milk production and dairy farm profitability in the U.S., against the backdrop of climate change. This study investigated 4 heat abatement strategies, including Minimal (open barn or shading), Moderate (forced ventilation), High (fans and misting), and Intense (air conditioning), for their technical and cost effectiveness. Heat stress and subsequent impacts on milk production per cow across 9 climatic regions in the U.S. were estimated for Early (2015-2034), Mid (2045-2064) and Late (2081-2100) 21st century, using climate projections for the Representative Concentration Pathway 8.5. Heat abatement treatments were then used to adjust predicted milk production losses and illustrate the potential to reduce heat stress related milk production losses and increase net profits. Economic analysis included a cost-benefit ratio calculation associated with the implementation of each heat abatement. Milk production losses accelerated across the U.S. at a mean rate of 174±7kg/cow per decade, and was fastest in the Southeast region. Heat relief with Moderate, High, and Intense abatements generally slowed milk production losses. Under those three abatements, national milk production per cow per year relative to Minimal heat abatement can be expected to increase by 3%, 4%, and 6% during Early-21st century, 3%, 6%, and 11% during Mid-21st century, and 3%, 8%, and 21% during Late-21st century, respectively. However, reduced milk production losses were not cost-effective in all the regions, especially during Early- and Mid-21st Century. Cost effectiveness increased with subsequently stronger heat abatements. In Mid-Late 21st century, mean annual net profits due to High and Intense heat stress abatement will approach $76-$8,145 and $131-$34,801, respectively, with largest net profits in Late-21st century under Intense abatement. Findings from the study demonstrate the value of downscaled climate data in shedding light on local and regional strategies that can abate dairy heat stress and mitigate potential milk production losses due to climate change.