Lameness is one of the most common health problems in dairy cows. It is also a welfare concern for individual cows and for the entire dairy industry. Some causes of lameness like digital dermatitis are relatively well understood, at least to the point that it is possible for most herds to be able to implement preventive programs.
Diseases like sole ulcer and sole hemorrhage (bruising) are not as well understood. Both ulcers and hemorrhage are found at predictable stops on the foot. This area is an impact zone directly below the last bone in the cow’s foot. There are a number of theories of how these diseases occur but we still don’t fully understand them. One theory is that laminitis following rumen acidosis might weaken the support structures inside the foot, making it more susceptible to damage. A few years ago, researchers proposed that cows that are thin or which suffer excessive weight loss also lose some of the natural cushioning inside the foot. That cushioning is provided by a pad of tissue that sits between the bone in the foot and the sole of the hoof. Fat is a big part of that pad of tissue.
You can measure the thickness of the pad using ultrasound. That’s how people first discovered that there may be a link between the thickness of the pad and lameness. Dairy cows with certain types of lameness were more likely to have a thin pad of tissue between the foot bone and the sole.
When the link between a thin pad and an increased risk of lameness was proposed, it was not clear what the link meant. Does thinning of the pad lead to lameness? Does the pad get thinner as the cow loses body condition? Are thin cows more likely to become lame because their cushioning foot pads grow thinner as the cow herself gets thinner?
When you measure both lameness and the thickness of the pad only once, you have no real way of knowing how the two are related. A recent study from the UK tried to figure out if changes in the thickness of the pad were linked to changes in the risk of a cow becoming lame. They followed cows from eight weeks before freshening to 29 weeks after. They measured pad thickness and back fat thickness too. They scored for lameness every two weeks.
Like the other researchers, they found that if the pad was thin, the cow was more likely to get a sole ulcer or hemorrhage but the thickness of the pad was only linked to a cow being lame for the outside claw.
They looked at what happened when the pad changed to become thinner or the cow herself became thinner. First of all, as cows went through their lactation, the pad did become thinner and cows did get thinner, the way almost all lactating cows do.
Being thin or losing weight increases the risk for getting a sole ulcer or hemorrhage but that isn’t true for thinning of the cushioning pad itself. If the cushioning pad becomes thinner, cows don’t have an increased risk of getting ulcers or hemorrhage. This can only mean that the increased risk of getting ulcers/hemorrhage when cows are thin or are losing weight is not related to any thinning of the foot pad that would naturally occur when a cow loses weight.
So sole ulcers, sole hemorrhages and lameness seem not to be due simply to thinning of the foot pad that occurs when dairy cows lose weight. However, thickness of the pad does seem to be important. We just don’t know how or why.