Three-dimensional triad of Heat stress, Comfort, and Lameness (HCL) in dairy cows: Breaking the lameness cycle through integrated management of comfort and heat stress using the "HCL Triad" model

Backgroun: Comfort of dairy cows has a decisive effect on their health, production, and productive lifespan. Despite significant advances in understanding pathogenic mechanisms, lameness remains one of the major challenges of the global dairy industry, affecting on average about Twenty-two percent (22%) of dairy cows. Since welfare and environmental factors play a key role in the occurrence of non-infectious claw horn lesions (CHL) in dairy cows, these factors have been examined in this review study.
Objective: To introduce the "HCL triad" (Heat Stress, Comfort, Lameness) and investigate the complex and bidirectional relationship between these three factors.
Material and Methods: A review study was conducted using published sources in the field of comfort, heat stress, and lameness in dairy cows from reputable national and international journals and conferences.
Results: Comfort and heat stress affect the pathophysiology of lameness not only through cow behavior (pressure theory) but also through physiological and genomic pathways. Lameness, by altering animal behavior, exacerbating heat stress, and reducing comfort, creates a vicious cycle. Since each of these three events affects the others, the starting point for breaking the cycles varies depending on the herd and geography, requiring a study of the management and environmental processes of that region.
Final Conclusion: Since lameness or heat stress ultimately leads to a reduction or loss of dairy cow comfort, providing a comprehensive framework to understand the relationships between these three events and emphasizing management strategies based on animal comfort will lead to the successful control of claw horn lesions in dairy cows.