Lameness is often viewed as one of the most critical issues facing the sheep industry in Ireland today.
Not only does lameness severely impact on welfare, but can also impact on sheep productivity, resulting in reductions of up to 15% in ewe conception rates, 20% in body condition scores and 20% in ewe conception rates (in comparison to sound ewes).
The cost alone of lameness to the sheep industry is estimated to be €5 million annually.
Many farmers commonly accept lameness rates of more than 10%. However, the ideal target should be no more than 5% of lame sheep in the flock at any one time. Foot rot is the most common cause of lameness and is present on more than 90% of farms.
Foot rot is a highly infectious bacterial disease caused by two separate bacteria, Fusobacterium necrophorum and Dichelobacter nodosus. F. necrophorum which can also cause foot scald is found in the gut and faeces of all sheep. Feet of affected sheep are the main source of infection within the flock. Foot rot is typically characterised by a foul smell and under-running of the hoof wall. Although infection can occur at any time, outbreaks tend to happen more frequently during the spring and autumn months when environmental conditions are more favourable.
Other common conditions implicated in lameness include scald and contagious ovine digital dermatitis (CODD). Scald which is a precursor to foot rot is often characterised by reddening and loss of hair between the hooves. It can be easily controlled by appropriate foot bathing.
CODD on the other hand, is a much more severe condition in which infection initially starts at the coronary band before leading to under-running of the hoof wall and complete avulsion of the hoof wall from underlying tissue. CODD is often viewed as one of the most severe foot conditions affecting sheep. Cases of CODD which have resolved after infection are often left permanently lame due to changes to underlying tissues and bone within the hoof. CODD is an extremely difficult condition to treat and results can be variable after antibiotic treatment and antibiotic footbaths.
When investigating lameness on farm, it is essential to involve your veterinary practitioner as early as possible to obtain a correct diagnosis and to implement an effective control plan. The following five-point plan has been used successfully in many farms with foot lameness problems and is outlined as follows:
1. Treat – An essential component of any control plan is treating all clinical cases of lameness. This must include the use of an injectable antibiotic for all cases of foot rot or CODD. Foot trimming should be kept to a minimum. Although routine foot trimming is commonplace on many farms, much research has concluded that it can increase levels of lameness. Recent studies have shown that routine trimming may lengthen the time it takes for hooves of lame sheep to heal.
2. Avoid spread – Both foot rot and CODD are highly infectious diseases and are easily transmitted between sheep particularly around areas of high sheep traffic. Appropriate footbaths can be implemented in consultation with your veterinary practitioner to help reduce the spread of disease. Sheep should stand for up to an hour after foot bathing before going onto clean pasture which has not been grazed by sheep for the previous two weeks.
3. Cull – Persistent offenders i.e. sheep which have not responded to two successive treatments, should be culled from the flock. These ewes are a continuous source of infection to the rest of the flock.
4. Quarantine - All incoming sheep should be quarantined for a minimum of four weeks before entering the flock. On arrival feet should be examined and foot-bathed. No lame sheep should ever be introduced to the flock.
5. Vaccination - Vaccination has been shown to reduce levels of foot rot significantly by protecting individual sheep and lowering the level of challenge on farm. The foot rot vaccine contains ten different strains of D. nodosus, the bacterium implicated in causing foot rot infection. All animals must receive a primary course of two injections six weeks apart. Booster injections are required three weeks before the next period of risk. Recent research has concluded that by controlling foot rot, the incidence of CODD can also be reduced. Through vaccination, the incidence of CODD can be reduced by up to 32%.
Through implementing the five-point plan and routine consultation with your veterinary practitioner, a target of 5% lame sheep at any one time can be more achievable. This in turn will significantly improve the welfare, productivity and viability of your sheep flock.