The role of the digital cushion in lameness prevention

Vet Sara Pedersen gives an update on the latest research on the digital cushion in dairy cows.

The last few years has seen us add significantly to our knowledge surrounding the digital cushion and its role in lameness prevention. The ‘do thin cows go lame or lame cows go thin’ quandary was addressed by Randall et al. (2015) who demonstrated that maintaining body condition score (BCS) has an important role to play in preventing lameness. Cows with a BCS<2 were significantly more at risk of lameness with a BCS of ≥2.5 being suggested as optimal from a lameness prevention persepctive. 

Based on the previous work of both Bicalho et al. (2009) and Newsome et al. (2017a&b) we know that BCS and digital cushion thickness are related so it can be hypothesised that maintaining BCS, maintains the digital cushion. It is a misconception that the digital cushion acts as a ‘shock absorber’ since the type of fats contained in the digital cushion dissipate rather than absorb forces, therefore a compromised digital cushion will have a reduced ability to dissipate the concussive forces that occur during walking away from the vulnerable sole area of the foot and to the stronger, weight bearing walls. 

So, we know that BCS is important in maintaining a healthy digital cushion, but what other factors impact on its ‘health’? Whilst we’ve established that lameness leads to pathological changes on the pedal bone (Newsome et al. 2016) the full circle hadn’t been completed in terms of how this then impacts on the digital cushion. It was postulated that the inflammation associated with claw horn lesions (CHLs) could lead to utilisation of the fatty acids in the digital cushion as inflammatory mediators or the development of scar tissue, thus reducing its ability to dissipate strike forces. 

A recently published paper by Wilson et al. (2021) sought to understand the relationship between the digital cushion volume and the lameness history of the animal. A total of 196 hind feet from 98 cows culled from the SRUC’s Crichton Royal Farm were included in the study to assess digital cushion volume. A subset of cows with an extensive lameness history was also analysed further. 

Here are some of the key findings: 

• The total volume of the digital cushion in the lateral claws was significantly less than in the medial claws.
• There was a strong correlation between the volume of fat within the digital cushion and its total volume.
• There was a large range in the digital volume cushion in the lateral claws between cows and in some instances, there was no digital cushion at all (range 0-30mL; Figure 1)!
• Cows with a history of lameness or that had an increased lameness score in the 4 weeks before culling were more likely to have a reduced lateral claw digital cushion volume.
• Digital cushion volume was negatively correlated with the number of lameness events or CHLs recorded in the animal’s history.
• Cows with a BCS>3 or an increasing BCS in the last 4 weeks before culling had an increased lateral claw digital cushion volume.

So, what does this mean? 

This is the first time that digital cushion volumes have been studied rather than just assessing digital cushion thickness and it’s identified that there is a large variation between cows. As well as variations between individual cows there can also be large variations between each of the three cylinders that make up the digital cushion in the lateral claw, in some cases one or more of the cylinders may be absent. It also demonstrates a clear deterioration in digital cushion volume with an increasing number of lameness events or CHLs.

The authors propose that the variations seen were due to a combination of genetic, developmental and disease derived factors occurring throughout the animal’s life. Variations in digital cushion volume arise initially from animals having different genetic potentials for the development of the digital cushion. This is then influenced (positively or negatively) through management during the rearing period, setting the scene for how ‘robust’ the animal’s foot is to the future development of claw horn lesions. Once an animal has experienced a CHL, this impacts on the digital cushion and increases her susceptibility to further lameness events and the chronic cycle of lameness begins. 

The results of this study add significant weight to ensuring that cows get off to the best start by creating a robust foot which underpins Success Factor Two of the Healthy Feet Programme.

Figure 1. Taken from Wilson et al., 2021. A histogram of the combined digital cushion volume from the hindfeet of 57 cull dairy cows. The bottom reconstruction images (plantar view) show the digital cushion (yellow areas) in relation to the other tissues of the foot (grey areas). The images show cows with low (A), moderate (B) and high (C) digital cushion volumes.

References 

Bicalho, R.C., Machado, V.S. and Caxieta, L.S. (2009) Lameness in dairy cattle: A debilitating disease or a disease of debilitated cattle? A cross-sectional study of lameness prevalence and thickness of the digital cushion. J Dairy Sci 92: 3175-3184. 

Newsome R, Green MJ, Bell NJ et al (2016). Linking bone development on the caudal aspect of the distal phalanx with lameness during life. J Dairy Sci 99(6): 4,512-4,525. 

Newsome R, Green MJ, Bell NJ et al (2017a). A prospective cohort study of digital cushion and corium thickness. Part 1: Associations with body condition, lesion incidence, and proximity to calving. J Dairy Sci 100 (6): 4745-4758. 

Newsome R, Green MJ, Bell NJ et al (2017b). A prospective cohort study of digital cushion and corium thickness. Part 2: Does thinning of the digital cushion lead to lameness and claw horn disruption lesions? J Dairy Sci 100 (6): 4759-4771. 

Randall, L., Green, M.J., Chagunda, G.G., Mason, C., Archer, S.C., Green, L.E. and Huxley, J. (2015) Low body condition predisposes cattle to lameness: An 8-year study of one dairy herd . J Dairy Sci 98 (6): 3766-3777. 

Wilson JP, Randall LV, Green MJ, Rutland CS, Bradley CR, Ferguson HJ, Bagnall A, Huxley JN. 2021. A history of lameness and body condition score is associated with reduced digital cushion volume, measured by magnetic resonance imaging, in dairy cattle. J Dairy Sci. Article in Press. DOI:https://doi.org/10.3168/jds.2020-19843