New computer model shows cost of Mycoplasma gallisepticum in laying flocks

Mycoplasma gallisepticum is one of the most common respiratory diseases in poultry, but how much does it really cost and what is the best approach to combat it?

Respiratory diseases caused by Mycoplasma gallisepticum (MG) can devastate flocks, but is treatment or vaccination really financially viable? Until now, it has been difficult to calculate the real costs of MG infection, or to weigh up the benefits of different treatment or preventative approaches.

But a new model created by the University of Reading will enable vets, consultants and producers to calculate the exact cost benefit of tackling the disease in individual circumstances.

It is the second phase of the £250,000 DEFRA-funded Farm Health Planning Project, which works across the industry to develop cost-benefit models to help producers tackle common livestock diseases in the most cost-effective way.

“This really is a useful tool,” says Daniel Parker, a poultry vet at Slatehall Veterinary Practice in Cambridgeshire, who helped to develop the model. “MG is becoming a lot more common in commercial layers and often it opens the door to other infections, like bronchitis, on top.”

MG is a bacterial infection which causes respiratory disease, leading to a drop in egg production and an increase in second grade eggs due to poor shell quality. “Invariably, you will get a secondary E coli infection, possibly with septicaemia, which causes mortality,” says Mr Parker.

Infection is usually diagnosed through routine blood tests or nasal swabs and the disease can then be treated with antibiotics. However, it can also be prevented by vaccination and the model can help producers to choose the most cost-effective option.

“There are a significant number of commercial laying flocks being vaccinated against MG,” says Mr Parker. It is most commonly transmitted between flocks, so is more prevalent on multi-age sites. “Good biosecurity will limit the risk, but MG goes rapidly through an infected flock because they share drinking water. In a multi-age system with a history of infection, vaccination has a clear benefit.”

However, free-range or single-age systems may not find such a benefit – although the age of infection has a dramatic impact on profitability, he adds. “If you get infection at 28 weeks the impact will be far greater than if you get it at 50 weeks of age.”

The web-based model allows producers to input farm specific details like egg prices and disease assumptions, including age of infection and then to explore the associated cost of outcomes, depending on the measures taken, says Isobel McClement, research assistant at Reading University.

It can track the impact of changes on a weekly basis, up to 80 weeks of age and includes sensitivities like withdrawal periods following treatment with antibiotics and loss of income through second grade eggs. It enables producers to compare the cost benefits of vaccination, antibiotic treatment or no action whatsoever, on both intensive and free range systems.

Assuming infection at week 28 in a flock of 9000 free-range hens with a laying cycle of 80 weeks, the model shows that producers will lose £57,253 in reduced egg output, seconds and mortality if they take no action at all. This is based on a large egg price of £1.04/doz, medium eggs at 78p/doz and seconds at 20p/doz.

However, if the producer was to treat the flock with antibiotics, at a cost of £410, the losses fall to £9381. This assumes a product with no withdrawal period – although the model can account for withdrawal periods if necessary, explains Miss McClement.

In this particular example, the vaccine presents the best option, costing just £450 – a potential saving of £56,803 against taking no action whatsoever and £8931 less than using antibiotics. Obviously, the situation changes according to the system, egg price, and time of infection, so each producer will find a different solution to suit them best.

“This model quantifies the costs of MG in laying hens and helps producers to examine the benefits of different treatments in their individual situations,” says Miss McClement. “The model is there to generate dialogue and awareness of disease costs between the vet and their client. The information can then be used to support the decision making process – not replace the decision maker.”

The model can be accessed free of charge.