OPINION: Foot problems most common reason for lameness — but not easy to cure

Lameness is a very common problem in dairy cows. There are numerous causes for the lameness but foot problems are most common. Sole ulcers, sole hemorrhages and white line disease (WLD) are three foot conditions that are often grouped because they are commonly seen during foot trimming and there is some evidence that they could be related to each other.

As with other diseases, preventing lameness is usually way better than treating it. This is one reason why routine and consistent foot trimming is more beneficial than treating cows with sore feet. Developing an effective prevention plan usually means having at least a basic understanding of why the disease happens. Because sole ulcers are so common and occur at the same place on the foot, there has been speculation that the key to prevention lies in better understanding the anatomy inside the hoof.
Years ago now, it was proposed that sole ulcers and maybe sole hemorrhage and WLD are due to changes inside the foot that we could manage.

Researchers used an ultrasound to look inside the foot. They discovered that the ‘digital cushion’ inside the foot could play a role in lameness. The digital cushion is a pad that sits between P3, the last bone in the foot, and the sole itself. Using ultrasound, they measured the thickness of the cushion in healthy and lame cows. They found that cows with sole ulcers were more likely to have a thin cushion. The hypothesis was that the thinner cushion might not protect the inside of the sole from P3 when cows were standing or walking. It might be easier for cows with a thin digital cushion to damage the sensitive part of the sole. Damage to the sole was suspected to predispose cows to develop an ulcer.

Dairy farmers and researchers already know that thin cows and cows that lost body condition post-fresh were at higher risk of becoming lame. When it turned out that thin cows and cows that had lost body condition were also more likely to have a thinner digital cushion, it was easy to believe that thin cows were more at risk of becoming lame because they had a thinner digital cushion. This was a classic example of research investigating whether two events are associated. If the research finds that there is an association between two events, that is not the same as finding that one event causes the other. It might be that both events tend to occur together.

So, the next step after finding that cows with thinner-than-average digital cushions are more likely to be lame from ulcers, hemorrhages or WLD is to investigate what the relationship might be. One way to do that is to follow cows over time. There are several research trials that have done exactly that. Sadly, they have not always discovered the same relationship between cushion thickness (or change in cushion thickness) and risk of lameness.
That doesn’t mean that the thickness of the digital cushion is not important; it just means that there are other things that are also important like the cows themselves, the barn environment or even the milking system (milking system can affect how long cows need to be standing on concrete). We don’t fully understand the relationship between the thickness of the cushion and lameness. One researcher even checked to see if there might be a problem in how we measure the thickness of the cushion – it is not clear whether it is best to measure with the cow’s foot off the ground or with her standing on the foot.

Right now, this is a classic example of finding an association between an event and a disease. It is easy to be lulled into thinking that the event causes the disease but that might not be true. The danger of making that assumption is that you could expend a lot of effort in changing the risk of the event but you might end up having little impact on the disease.
With digital cushion thickness, genetics researchers even looked to see if the thickness of the digital cushion had a strong enough heritability that you could improve it through selective breeding. It turned out that you could, even though making improvements in overall lameness through breeding seems not to be so easy.