Economic effect of pneumonia and pleurisy in lambs in New Zealand.

AIM

To estimate the cost of pneumonia and pleurisy in lambs to the sheep industry in New Zealand, in order to provide a reference for future cost-benefit calculations for control programmes to reduce the incidence of pneumonia.

METHODS

An estimate of the economic cost of pneumonia and pleurisy in lambs was based on: cohort studies of the association between growth rate and the extent of pneumonic lesions at slaughter (n=14 flocks), the prevalence of moderate to severe (MS) pneumonia (> or =10% lung surface area affected) and pleurisy (n=1,719 flocks), the correlation between the prevalence of MS pneumonia and economic loss at the flock level, and data on annual slaughter statistics and carcass value in New Zealand. A stochastic spreadsheet model was developed and run with 1,000 iterations. Input variables represented by probability distributions were growth rate, average cost of loss according to the prevalence of pneumonia per month, carcass value, prevalence of pleurisy, and carcasses downgraded for pleurisy, and annual national slaughter statistics. The output was a posterior distribution of the annual cost of disease.

RESULTS

The cost of pneumonia only included the loss associated with reduced growth rate, while mortality due to pneumonia was assumed to be low and was ignored. The cost of pleurisy included the loss associated with downgraded or condemned carcasses. Thus, the simulated annual average cost of pneumonia was NZ$28.1 (95% CI=NZ$15.0-42.0) million, and that of pleurisy NZ$25.1 (95% CI=NZ$10.2-48.1) million. The combined cost of pneumonia and pleurisy averaged NZ$53.2 (95% CI=NZ$32.4-78.9) million. The parameters with the greatest impact on the combined cost of pneumonia and pleurisy were prevalence of pleurisy between March and May, and cost of reduced growth due to pneumonia for lambs slaughtered in June.

CONCLUSIONS

The average cost of pneumonia and pleurisy to the sheep industry in New Zealand due to reduced lamb growth and decreased carcass value is likely to be between NZ$32.4 and $78.9 million. This is a conservative estimate, omitting mortalities, indicating that pneumonia and pleurisy have substantial economic impact on sheep farming in New Zealand. Considering that 23,833,000 lambs were slaughtered in 2003/2004 (average value $65.56/lamb), this cost would equate to NZ$1.36-3.31 per lamb.

CLINICAL RELEVANCE

Pneumonia and pleurisy are common diseases in lambs in New Zealand, leading to substantial economic loss to producers.