Since it first appeared in the 1970s, bovine digital dermatitis (DD) has become endemic within the UK dairy herd. Alongside being a great welfare concern, the economic consequences of DD are substantial and include significant reductions in milk yield and reproductive performance.
The family of bacteria known as the treponemes have been identified as important aetiological agents in DD. These bacteria are highly contagious and are found within ulcerative lesions typically occurring between the heel bulbs at the heel-horn junction. Once DD lesions are established the host often remains infected for life, even if the lesions appear to heal. Chronic lesions may revert to the active stage and become a source of infection for other cattle. Digital dermatitis lesions can be classified by the M-stage scoring system (Dopfer et al., 1997; Berry et al., 2012).
Two things increase the likelihood of a foot becoming infected with DD
Damaged skin: The bacteria can only enter and become established in the deeper layers of the skin if the skin is damaged. This includes damage from being in contact with slurry. Skin which is in constant contact with slurry is more permeable and is more likely to become infected. Foot conformation, particularly having a lower heel height may increase slurry contact.
Contact with DD bacteria: The bacteria associated with DD can survive in slurry for up to 24 hours. A higher prevalence of active DD lesions will increase the likelihood of feet coming into contact with infected slurry.
Treatment and control of DD
The cornerstone of controlling DD is to quickly identify and treat active lesions. This requires regular visualisation of the feet. Lameness is an unreliable indicator of infection as studies have shown that only 39% of cattle with active lesions are lame. Clean hind feet can be visualised using the “mirror stuck to a spatula” method in the parlour, as an alternative to lifting feet in a crush. Treatment consists of washing the foot, removing any loose scabs, drying the lesion, and spraying with topical oxytetracycline spray. Lame cattle should also receive non-steroidal anti-inflammatories.
It is useful to adopt a unique method to visually identify treated cattle, such as using different coloured marker sprays so that they each get the required number of repeat treatments (for best results, repeat treatment daily for 3-4 days). Disinfect gloves and hoof knives between cows and between feet. DD bacteria have been shown to survive for at least 2 hours on hoof knives. Suitable disinfectants are 1:100 FAM30®, 2% Virkon® and 2% sodium hypochlorite. A contact time of 20 seconds will remove DD bacteria. Clean, dry conditions promote healthy skin which is resistant to infection.
Improve Floor Hygiene
• Minimise slurry pooling and avoid slurry cross-contamination between adults and youngstock.
• Run automatic scrapers at a frequency which prevents slurry and urine pooling excessively. • Robotic slurry vacuums can help to minimise slurry pooling and avoid slurry waves which often occur in front of automatic scrapers.
• Improving cubicle comfort will encourage the proper use of cubicles and promote increased lying times, reducing the contact of heels with slurry.
• Clean, dry conditions promote healthy skin which is resistant to infection.
Footbathing
A good footbath should ensure good cow flow and be 3.5m long and 12cm deep, with a non-slip surface. It should be easy to fill, empty and clean. The floor of the bath should be at the same level as the approach and exit floor. Automated footbaths avoid the need to handle chemicals and save time. As a general rule, allow 1 litre of solution per cow passage. A separate footbath should be incorporated into the heifer housing or management areas. The frequency of foot-bathing depends on the prevalence of DD, the type of lesions, and the cleanliness of the feet. It is better to increase the frequency of footbathing, than to increase the concentration of the footbath solution. Be sure to follow the manufacturers instructions as to the chemical concentration needed The genetic heritability for the risk of DD is relatively low (0.40), although it is still advantageous to select bulls with positive DD index values, as genetic improvement is cumulative. As always, maintaining good biosecurity is essential to avoid bringing in different strains of the causal bacteria.
Thank you Heather Millward of Oakhill Farm Vets.
