Four footrot fallacies

Tablelands Telegraph - September 2020

Dr Nigel Gillan

As the District Vets highlighted in our August Edition of Ag Advice, prolonged wet conditions have brought about lots of lameness in sheep. These seasonal conditions (combined with an increase in sheep introductions as restocking occurs) mean that sheep producers should be particularly aware of footrot risks this spring.

Footrot can be a complex disease, and sometimes it's hard to sort the fact from the fiction.

Our District Vets are available to answer any questions you have – at the end of the day, our aim is to help our Central Tablelands sheep producers stay footrot-free. As a start, here's a quick fact-check on a few opinions you might have heard:

1. "Lameness just occurs whenever sheep are standing in wet paddocks" (aka "they just have soft feet"). Yes and no. Wet conditions clearly do predispose sheep to a range of foot issues – foot abscess being the most common. It's also possible for sheep with soft, wet hooves to be slightly lame due to sole bruising from catheads or stones. However, true 'under-running' of the sole of the hoof really only occurs when the footrot bacteria (D. nodosus) is present.Wet conditions alone will never cause these types of lesions.
2. "If there's not severe lameness, it can't be footrot". There are lots of different strains of D. nodosus, and they don't all cause the same level of under-running and lameness. The critical distinction to be made is between 'benign footrot' (which isn't a regulated disease, and doesn't result in restrictions on the sale/movement of sheep), and 'virulent footrot' (which does have regulatory implications). Under ideal environmental conditions (high rainfall, warm temperatures, and abundant pasture), really nasty 'virulent' strains can cause the nightmare lesions you may have heard about – entire hooves rotten and flyblown in a large percentage of sheep. But not all strains will create this level of damage so quickly, and environmental factors influence the amount of lameness seen. Many parts of our region are still a bit too cold for footrot to fully express, so what looks like mild disease now could flare up as we enter spring.
3. "A lab test can provide an instant diagnosis". Lab testing options are available, and vets can use these to help make a diagnosis, but a lab test alone can never provide a clear-cut answer. Ultimately, distinguishing between benign and virulent footrot depends on visual examination of a large sample of sheep under suitable environmental conditions, in order to get an accurate picture of what the disease is doing at a flock level. Although this can be an involved process, it ensures we aren't being too hasty to jump to a diagnosis. Given the serious implications of virulent footrot, taking the time to reach an accurate diagnosis is in everyone's interests.
4. "Zinc sulphate will make the problem go away". There's no doubt that a zinc sulphate footbath is a very effective way to reduce the severity of benign or virulent footrot lesions, and it should be used when needed. That said, it's important to keep in mind that zinc sulphate will never entirely remove D. nodosus from the flock. Some bacteria will always persist in the upper layers of the skin or in pockets of under-running in the sole. This means that zinc sulphate is great for suppressing footrot (and reducing its spread from sheep to sheep), but it will never totally eradicate the disease. For this reason, it's best to have any suspicious foot issues checked by a vet, so that a complete treatment or eradication program can be implemented.