A better understanding of a structure in cattle known as “the digital fat pad” is possibly the most exciting recent advance in the lameness control.
The increased knowledge of this ingenious piece of natural design is helping us appreciate why some animals are more at risk than others and, crucially, how to reduce lameness across the herd.
What is the digital fat pad?
The digital fat pad, or fat pads, is made up of three parallel, roughly cylindrical structures that begin as a cushion beneath the heal and run towards the toe. They consist of an outer capsule of strong connective tissue that is filled with fat.
Essentially, they are nature’s version of the air-cushioned running trainer and are there to fulfil a similar role.
Changes in these fat pads and differences between groups of cattle are thought to contribute to certain causes of lameness, namely sole bruising and sole ulcers.
Cattle rely heavily on structures within the hoof capsule that support the foot by absorbing the energy and forces of locomotion. We now know this is largely provided by the digital fat pads.
Research has shown first lactation heifers are more prone to traumatic hoof lesions (bruising, sole ulcers and white line disease) and knowledge of the digital fat pads can help to explain this.
Why are heifers high risk?
The fat pads of heifers have been shown to contain less fat than those of cows. Not only that, but there is a lower proportion of “soft” fat. In fact, the fat pad of cows does not reach full shock absorbency until into the third lactation.
This is in a group of animals that can be high risk for other reasons as well. They are often undergoing the greatest management changes around calving; non-milking to milking, small group to larger group of mixed ages, increased standing times, greater metabolic stress, a change in housing type.
To go back to the earlier shoe analogy, these high-risk animals are wearing clogs compared to the soft, cushioned, top-of-the-range running trainers of a third lactation animal.
To make matters even worse for these animals there is evidence that suggests their underdeveloped fat pads may even act as a reservoir for inflammatory compounds, meaning the response of the foot to injury or trauma may be even greater than that of a cow.
Why does calving increase risk of lameness?
So what is it that occurs in the fat pad around calving that increases the chance of lameness, particularly in heifers?
The concept of negative energy balance and fat mobilisation in early lactation is well known and it is possible that this fat metabolism is replicated in the digital fat pad, as it is in other areas of the body.
It would also appear that the fat composition, both the types of fat and the total amount of fat, changes around this time, particularly in the presence of metabolic disorders, for example fat mobilisation and ketosis.
The incidence of sub-clinical ketosis is probably widespread in many high-yielding dairy herds and so to, it is likely, are changes in the digital fat pads of these cows.
It has also been shown that housing type and calving have effects on the structure and function of the fat pad with cubicle housing and excessive standing periods reducing its effectiveness as a shock-absorber.
These changes ultimately result in poor fat coverage, and so cushioning, of the area prone to sole ulcers.
This can help to answer the perennial question: are lame cows thin because they are lame or are thin cows more likely to be lame?
Armed with this information we can look at adopting practices to minimise changes in this crucial structure in the foot and the challenges put upon it:
- Aim for a body condition score in heifers, at calving, of 2.5-3.0. This will minimise condition loss and fat mobilisation, including from within the digital fat pad.
- Consider a heifer group to minimise the effects of bullying and the stresses associated with calving.
- Consider a post-calving hoof trim. This will allow you to spot and treat the early signs of a developing sole ulcer. The exact timing of this trim should be discussed with the foot care team on your farm.
- Maintain low stocking densities in fresh calved groups to encourage maximum lying times and reduce stress.
- Optimise cow comfort in this group, again to increase lying times.
- Minimise standing times in at-risk animals, particularly around milking. A small, fresh cow group with a fast milking turnaround can help to achieve this.
There may be future opportunities to manipulate the diet to modify the types and content of fat in the digital fat pads, and help protect against traumatic lameness.
However, even with the knowledge we now have, and adopting the strategies outlined above, we can further reduce lameness in our dairy herds and save cost to boot.