A history of lameness is associated with reduced proportions of collagen type I relative to type III in the digital cushions of dairy cattle

Hoof horn lesions (HHLs) are highly prevalent and recurrent causes of lameness in dairy cattle globally. The digital cushion is comprised of three cylinders of adipose tissue embedded in a system of collagenous connective tissue which are designed to reduce the risk of HHL onset. Previous research has identified that animals with a history of lameness and HHLs are more likely to have a reduced digital cushion volume in their lateral claws, but the impact on the histological structure remains unknown. Collagen is an important fibril related to adipose tissue structure and function, but its role in the digital cushion is poorly understood. Our study aimed to examine the proportions of type I and type III collagen within the digital cushions of dairy cattle at cull, and to investigate associations with digital cushion volume, and lameness and HHL occurrence throughout the animal’s life. This retrospective cohort study resulted in 599 digital cushions being dissected from the hind feet of 54 animals. Digital cushion tissue underwent Picrosirius Red staining, combined with systematic random sampling, and collagen content analysis. The results described the proportion of collagen that was type I, relative to the proportion that was type III. The proportion of type I collagen was used as the outcome variable in multivariable linear regression models. The median (min – max) proportion of collagen that was type I contained within the lateral and medial claws was 56.2% (23.6– 83.8%) and 59.6% (13.3 – 92.7%) respectively. The proportion of type I collagen was lower in animals that had a history of HHLs and lameness throughout their lives. Animals with a lower BCS at cull or were culled at a later parity had less type I collagen in their lateral claws at cull. Animals with a higher digital cushion volume also had an increased proportion of type I collagen in their lateral claws at cull. Our results have highlighted the histological impact that HHLs have on the structure of the digital cushion. We hypothesised that localised inflammation associated with HHLs was associated with a remodelling of the adipose tissue within the digital cushion, which would predispose the individual to a future of lameness and HHLs.