Computer calculations help beat footrot

How much does footrot cost your flock and, more importantly, do current treatment measures provide value for money?

The unfortunate truth is that many farmers are unlikely to know the answers to either of these questions.

But with the help of a new computer model, developed by researchers at Reading University, they may be able to get a good deal closer to the answers and to improving flock foot health.

Most UK studies show a footrot incidence rate of about 10%, with an average of about 3% of ewe cullings due to footrot, says Isobel McClement of the University’s department of Agriculture and Food Economics.

“But because cases occur over a long timespan, with only maybe one or two cases a week, few farmers recognise the true number of cases or the total cost to the flock.”

The model developed by Miss McClement, with colleagues Peter Cook and Richard Bennett, aims to help farmers tackle footrot by identifying both how much footrot costs the flock and how much treatment measures cost.

“Then it calculates whether treatment is economically justifiable,” she says.

But farmers need to remember that while footrot and scald hinder productivity and hence profitability, they can also be a serious welfare problem.

So while cost effectiveness is essential, so is ensuring animal welfare rules are not being compromised, says Prof Bennett.

Data required to run a cost:benefit analysis of foot conditions are relatively straightforward and the model allows farmers to vary certain parameters to more closely match farm conditions, such as treatment costs and time spent treating sheep.

The starting point is flock size and lambing percentage, along with average lamb sale weight and price, together with cull ewe value and replacement costs.

These data should be easily found in flock records.

Next it requires footrot incidence and culling percentage attributed to footrot, along with information on treatment choice, frequency of treatment, time spent treating the flock and treatment success rate.

The model also allows for the scenario of footrot being a problem in in-lamb ewes and the consequent lower lambing percentage which results from it.

Taking an example flock with 500 ewes, a footrot incidence of 12% (60 cases of footrot), a 3% culling rate and ewes being housed for lambing resulting in a 65% efficacy of treatment with a 3% formalin solution, the model was set to work.

With the flock housed, less time should be needed for treatment, as there is no need to gather them, so two hours labour was allocated to perform the task.

Other assumptions include a cull ewe value of 32, prime lamb values of 42 and replacement ewes costing 80.

This scenario revealed that footrot was costing the flock a total of 688, including 602.28, which represents the potential value of 14 lambs lost due to ewes being infected while pregnant.

Treatment in this case would cost a total of 41.46.

But as the flock was housed the efficacy of treatment would be reduced and footbathing would fail to cure all cases, believes Miss McClement.

“Ewes would be going back on to damp, clammy, infected straw bedding, increasing the chances of re-infection.”

A one-off treatment would result in 39 cases being cured, leaving a further 21 still infected and the potential for these sheep to re-infect cured sheep, or cause new infections in other flock members, she says.

“The total cost saving of this treatment would be 447.84, which, when you subtract the treatment costs of 41.46, leaves a total benefit of 406.18.

In theory in a flock with this level of infection a programme of five footbath treatments would cure all the cases, but this assumes no re-infections.”

A better option might be to treat cases by footbathing initially and then treat any persistent cases with topical use of terramycin spray.

Interestingly, when vaccination is included as a treatment scenario it fails to deliver a benefit in many circumstances.

But, bearing in mind the costs associated with treating 500 sheep this is understandable, believes Miss McClement.

“Vaccination can be useful where there is a major footrot problem, but in many situations the costs simply outweigh the benefits.”

When vaccination is the chosen method of treatment in a flock of 500 in-lamb ewes and a total of three hours was allowed to vaccinate the ewes, there is a small benefit.

However, it is questionable whether one man could gather and vaccinate that many ewes in that short a time, she adds.

But choosing just to vaccinate affected and high-risk sheep may prove cost effective and lead to improved footrot control, she says.

“Vaccinating 100 affected and high-risk ewes in a flock of 500 would involve a cost of about 104.46, but the model estimates the saving to be more than 440, leaving a benefit of more than 335.

In this situation vaccination may appear a much more viable option.”

Importantly, it must be remembered that this model only estimates the full costs of footrot in ewes and scald in lambs.

It is an aid to decision making and the results, therefore, should not be taken in isolation, she adds.