by Dr John Jardine
With the current wet winter and spring we have seen an increase in the number of reported cases of digital dermatitis (DD) on local dairy farms. Here we discuss the disease and its implications on your farm.
What causes DD?
DD or hairy heel wart is caused by an infection on the foot by Treponema bacteria. Treponema bacteria are shed from the feet and survive well in moist faeces. Infection to a new animal is from direct contact with the bacteria which can be aided by other bacteria and when the skin on the feet is damaged or macerated. Once a cow has contracted DD she is generally immune to that strain but is still susceptible to other strains. The severity of DD infection is extremely variable between farms and this has puzzled research scientists trying to control and eradicate the condition from dairy farms. Control procedures are time consuming, expensive, and can only be justified in situations where the disease is having a significant economic or welfare impact in the herd.
What does DD look like?
The typical DD lesion is between the claws at the back of the hoof. Lesions can also occur at the front between the claws and at the heel bulbs. 80% of DD lesions are on the hind feet.
DD lesions are classified by a scale:
M0 Normal skin
M1 A small, round lesion with a clear border, less than 2 cm in diameter. The surface is mottled red-grey with scattered bright red spots. The lesion will be painful to touch and cows will often limp
M2 Angry red-grey mottled lesion has grown larger than 2 cm. Painful when pressed
M3 Lesion is healing with a dry brown scab on the surface; no reaction from cow when lesion is pressed
M4 Lesion has become chronic with raised growths on surface, often has a warty appearance
In intensive farming situations such as free stall dairies DD is a significant cause of lameness in dairy cows. In Europe and North America it is the most common cause of lameness in dairy cows. On pasture based farms in Australia and New Zealand, DD has been found but it often does not cause significant amounts of lameness. In Australia there is a higher risk of DD causing significant issues when cows spend a lot of time on feed pads and on free stall farms. The prevalence of DD in Australia is not known as there have been no relevant studies performed here. The Taranaki region of New Zealand however, has similar cattle management practices and a study of 224 farms in that region found 64% of farms had DD lesions on some of their cows. In a later study on 57 of the positive farms the prevalence in the cows was between 1 and 13.7% with an average of 2.5%.
How is DD treated?
The best way to treat DD is by applying oxytetracycline to a swab and bandaging it in place. It should be left in place for 3 days. Alamycin spray is frequently used for this purpose. When used in this way there are no detectable levels of antibiotics found in the milk.
How is DD prevented?
The best method for controlling DD is to minimise the spread through good hygiene practices. This includes removing slurry frequently from where cows are standing eg. scraping around feeders and washing yard down, and foot bathing. There are several products that can be used in a footbath, copper sulfate (2.5-5% in foot bath) and formalin (4% in foot bath) are the two most commonly used. Each have their own issues. Copper sulfate has environmental issues with long term accumulation on the farm and formalin has OH&S issues. Foot bath design is very important however it is very farm specific depending on the exit of the dairy so please contact us for more advice.
If you don’t have DD on you farm the best method of prevention is to try to stop it coming onto your farm. This could be from new cattle arriving on your farm to hoof trimming equipment that has not been properly cleaned using a disinfectant.
What are the implications?
If you don’t have DD then try to prevent it occurring on your place.
If you have it but it does not cause issues then monitoring it to see if prevalence changes or lameness occurs from it would be recommended.
If you have an increasing prevalence or are getting lameness form it then a management protocol needs to be put in place to prevent it from having a significant impact on your farm.