Conditions ideal for lameness in sheep

Sheep producers across the region are reminded of the importance of monitoring their sheep for lameness through spring. There are various causes of lameness in sheep including ovine interdigital dermatitis, benign footrot, virulent footrot, and foot abscess. Lameness in sheep flocks can result in reduced weight gain and illthrift, poor joining, treatment costs, reduced sale prices, and in cases where ewes are affected close to lambing, death due to recumbency and pregnancy toxaemia.

Ovine interdigital dermatitis (OID) - also known as ‘scald’ - is a mild infection of the skin between the hooves of sheep. It is usually associated with lush, green, wet paddocks. When a sheep’s feet are constantly exposed to moisture, they become susceptible to bacterial infection. OID can then create a window for other more severe infection, such as footrot and foot abscess. Many sheep producers in the region undertake footbathing programs during winter using zinc sulphate, which acts as a topical disinfectant and has a drying effect on the feet. This practice can help to control OID and prevent more severe foot problems.

Footrot is an infection caused by the bacterium Dichelobacter nodosus, which breaks down the tissue between the horn and the foot and can result in painful separation or ‘underrun’ of the sole. Around 20 different strains of Dichelobacter nodosus have been identified in Australia and each strain has differing ‘virulence’ or ability to cause disease. Strains are classed as virulent if they have significant economic and welfare effects based on the proportion of sheep they infect and the severity of the lameness they cause. The bacterium is unable to infect a healthy foot and often occurs secondary to OID. Good control of OID can reduce the effects of benign footrot in a flock.

If a producer or veterinarian suspects virulent footrot in a flock, they have an obligation under NSW law to notify Local Land Services within 48 hours. LLS vets and biosecurity staff will then make a thorough assessment on the cause of lameness and can advise farmers on how best to manage the lameness and reduce impacts.

The number of flocks infected with virulent footrot in NSW has been significantly reduced since the NSW Footrot Strategic Plan was implemented in 1988. In August 2009 the entire state was declared a Protected Area as less than 1 per cent of flocks were affected.

Other states have different levels of regulation in relation to footrot. As such, it is a requirement to have a Sheep Health Declaration stating that sheep are free of virulent footrot when sheep enter NSW from interstate.

On-farm biosecurity is the best defence against introducing diseases and treatment-resistant parasites. This includes assessing the risk prior purchase and isolating or quarantining newly acquired stock from the existing flock. Boundary fences should also be well maintained to reduce the risk of disease spread by stray sheep. Footrot needs the right conditions, warm and wet, to cause disease. This could mean you may need to isolate newly introduced sheep for very extended periods to monitor them for lameness during the risk period during winter/spring.

Current conditions are conducive to lameness issues in sheep. Regular monitoring is important, especially in newly acquired sheep. If you have any issues or concerns please call your local District Vet or Biosecurity Officer to discuss - we have a lot of experience in working with sheep producers to plan a program to eradicate footrot on their properties.