Digital dermatitis is caused by Treponeme bacteria. Lesions usually develop in the skin on the heel bulb or interdigital space. The disease cycles though an active phase to healed or chronic. Once infected a cow will never be bacteriologically cured, the treponeme bacteria encyst in the dermis layer of the skin and become dormant, unless conditions are favourable for them to reactivate.
Lesions can be scored with the M-scoring system to define the stage of disease. M0 to M4.1 this is important for control and assessing active infection in a herd. ICAR have produced a useful guide.
The best way to score cows is to lift feet in a crush and inspect once washed and dried. However, usually for practical reasons, hind feet are inspected and scored in the parlour.
Fig 9: Pictures of Digital Dermatitis M scores 0-4.1, L to R.
The mainstay of treatment for digital dermatitis is topical treatment of active lesions, either antibiotics or non-antibiotic treatment. Systemic antibiotics are not needed for a digital dermatitis lesions. Systemic antibiotics are only warranted for ‘Foul’ in the foot lesions of infections of deeper structures i.e. P3 or the DIP joint.
Once lesions have healed, prevention of further outbreaks is key. The infected cow is the main reservoir of the treponema bacteria and presents the largest risk to uninfected cows through slurry transmission. The bacteria can survive for roughly 24 hours in liquid slurry, creating a short term reservoir. Key aspects of prevention centre on slurry control and foot hygiene.
- Biosecurity: Between herds, buying in cows and also within farm between groups and when trimming (between cows)
- Hygiene: Autoscrapers, crossovers and avoid pooling of slurry.
- Footbathing: Foot bathing to reduce bacterial load and infection risk by maintaining clean feet.
‘Blitz treatment’ can be used and has been proven to be effective. All cows are inspected at once for digital dermatitis and all treated at the same time. ‘Ad hoc’ treatment, of only a few infected cows over time allows constant maintenance of an environmental reservoir. By treating all cows with active/recurring lesions at the same time, this reduces environmental pressure and therefore assists in control, alongside other preventive measures.
Fig 10: The Digital Dermatitis cycle, topical treatment focussing on active lesions and hygiene focussing on prevention.
In 2016 a group of International Experts gathered to produce a 5 Point Plan for Digital Dermatitis Control. They recommended the following:
1. External biosecurity to keep disease out of farm.
2. Internal biosecurity to minimise infection pressure on cows (which includes slurry management).
3. Early identification, recording and treatment of clinical cases, in association with hoof care
4. Frequent foot disinfection to reduce new cases
5. Define and monitor targets
Foot disinfection or foot-bathing
Foot bathing is a method of cleaning and disinfecting feet. The bacteria causing digital dermatitis are easily washed off and killed by many disinfectants. Foot bathing needs to be done as frequently as is necessary in relation to the disease levels. Some farms will footbath every milking, some will footbath twice a week. Frequency should be decided using lesion records and in conjunction with your vet.
As a general guide the following points are referred to when thinking about a good footbath design:
- Long at least 3.7 metres – increases washing with more steps
- High kerbs – minimises “kick-out” of solution and shortens 1st and last step for more plunges
- Solid sides – using Temple Grandin principles for greater cow flow and reduce “kick-out” of solution
- Same level in and out – so cows step in and out confident about where levels are
- Comfortable surface on the base – rubber or grooved concrete