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

Abstract

Hoof horn lesions (HHL) are a highly prevalent and recurrent causes of lameness in dairy cattle globally. The digital cushion is composed of 3 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 HHL are more likely to have a reduced digital cushion volume in their lateral digits, 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, 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 relative proportions of type I and type III collagen. The proportion of type I collagen was used as the outcome variable in multivariable linear regression models. The median (minimum-maximum) proportion of collagen that was type I contained within the lateral and medial digits 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 HHL and lameness throughout their lives. Animals with a lower BCS at cull or that were culled at a later parity had less type I collagen in their lateral digits at cull. Animals with a higher digital cushion volume also had an increased proportion of type I collagen in their lateral digits at cull. Our results have highlighted the histological impact that HHL have on the structure of the digital cushion. We hypothesized that localized inflammation associated with HHL was associated with a remodeling of the adipose tissue within the digital cushion, which would predispose the individual to a future of lameness and HHL.