INVITED REVIEW: Why cows die in US dairy herds

Purpose: Over the past several decades there has been an appreciable, persistent, and concerning rise in dairy cow mortality. The purpose of this review was to integrate epidemiological, pathophysiological, and historical perspectives to improve our understanding of why dairy cows die and what can be done about it. Sources: Refereed scientific journal articles, USDA reports, and conference proceedings available in online databases were consulted in this review. Synthesis: Explorations of causes of dairy cow death frequently have focused on associations between mortality and population characteristics, management, and environmental factors. These studies often suggest that intensification of the dairy industry may influence high on-farm dairy cattle mortality. Other studies have focused on pathophysiologic descriptions of specific deaths, alongside the utility of incorporating postmortem evaluations into on-farm management. Although it is most certainly useful to establish broad associations between population characteristics or specific disease entities and higher death rates, mitigation strategies must be based on an understanding of why those associations or diseases are present in the first place. Conclusion and Applications: A multitude of factors and complexities act in concert to influence why cows die in US dairy herds. Understanding differences related to why cows die requires insight into the impacts of environment, operational practices, economic concerns, and animal interactions on overall performance. Although there are practical suggestions for addressing dairy cow mortality such as incorporating postmortem examinations and standardized nomenclature, questioning why dairy cows die is part of a larger discussion regarding the welfare of animals in modern agricultural systems.