Economics of BluetongueWritten by John Ritten
A study by recent UW graduate student Tris Munsick, with Drs. Dannele Peck in the Department of Agricultural and Applied Economics, Myrna Miller in the Veterinary Sciences Department and myself calculates the cost of bluetongue outbreaks on Wyoming sheep operations. The analysis is covers flock sizes from 256 to 1,440 ewes, with varying severities of potential outbreaks and timing of recurrences over a suite of prices. The results should be of interest to most sheep producers across the state.
The costs of an outbreak are manifested in a variety of ways, including the costs of caring for sick ewes – both the labor and feed costs associated with tube-feeding, drug costs and the loss of revenues due to both death loss and lower lamb weights due to delayed breeding.
Estimating the impacts of an outbreak can be challenging, as not all flocks respond similarly.
For example, we would expect flocks in the eastern part of the state to have lower costs as compared to flocks in the western part of state, mainly because outbreaks occur more commonly in the east and, therefore, flocks will likely have some form of existing immunity. When naïve populations are infected, we expect the impacts to be more dramatic and, therefore, more costly. To account for this variability, the costs were estimated over a suite of morbidity, or sickness, rates, and mortality, or death loss, rates, as well as lamb and ewe prices.
For brevity, I will only report the results from a hypothetical 640 flock. For an “average” outbreak with 21 percent morbidity, 12 percent mortality and lamb prices at the 20-year average, the total cost of a single bluetongue outbreak would be over $36,000. This represents a case in that just over one in five ewes is actually infected, and just over one in 10 dies. In the “worst-case” scenario, with 36 percent morbidity, 20 percent mortality and lamb prices at the peak of observed prices over the last 20 years, the total cost exceeds $72,000 for a single outbreak. In this case, over one-third of the flock is infected and one in five ewes dies.
The costs of an outbreak are obviously fairly high.
The study goes on to calculate the cost of vaccinating against bluetongue. I’ll report the costs associated with using a killed virus vaccine, which can be special-ordered to match the serotype in your region. If you are interested, talk to your vet or the Wyoming State Veterinarian. The assumptions regarding vaccination used in the study assume two doses are required at a cost of $1.20 per dose and that the vaccine is administered when animals are already being handled to minimize additional labor costs. While the vaccines are safe to use any time of the year, the study assumes vaccinations are done prior to summer grazing by June 1, so the flock is protected when returning to lower elevations in the late summer or early fall, when infection is most likely.
The study calculates the costs associated with various vaccination strategies, but given the fact that some protection remains for a period of two years, I will present the results from a strategy that vaccinates the entire flock every two years, and only lambs will need to be vaccinated in the other years. The annual cost associated with this strategy for a flock consisting of 640 ewes is $2,731 per year. This seems very cheap compared to the cost of an outbreak. However, this cost must be incurred every year, while outbreaks tend to occur less frequently. However, if an “average” outbreak occurs every five years, this strategy realizes a net benefit of almost $5,000 per year, even in years between outbreaks. Even if an average outbreak occurs only every 20 years, this strategy still has a net benefit of over $2,000 per year.
Results also show that the greatest cost factor associated with an outbreak is the mortality rate. Keeping ewes alive should greatly reduce the cost of the outbreak as it keeps breeding stock in the flock, reducing the need to buy or retain replacements.
The second biggest factor in terms of outbreak cost is lamb prices. Results suggest that vaccinating in years of high prices is a better investment than in years with low prices. However, we rarely know in advance exactly what prices will be in the fall, so I would recommend vaccination regardless of the price forecast.
Morbidity rate is the third most important factor, however the impact is only a third as large as mortality rate.
When making decisions regarding vaccinations, it is also important to understand the impact of location on the benefits of vaccination. In areas where bluetongue is more rare, we would expect higher morbidity and mortality rates as the flock has had less exposure, and therefore less existing immunity, to an outbreak. Areas that experience more frequent outbreaks tend to have lower morbidity and mortality, therefore the consequences of infection are less severe.
For example, if an area experiences a severe outbreak every 10 years, with 36 percent morbidity and 20 percent mortality, and assuming 20-year average lamb prices, the annual benefit to vaccination exceeds $6,000.
However, if a location experiences an mild outbreak every five years with only a nine percent morbidity rate and a six percent mortality rate, the annual net benefit of vaccination is only a little over $900 per year. In this case, even though outbreaks happen more frequently, the fact that they are less severe results in lower benefits of vaccination.
It’s important to consider a lot of factors when determining the larger benefit we see from vaccination. The more severe an outbreak is, the benefits of vaccination are larger. The more frequent an outbreak is, the larger the benefits of vaccination are, although only for outbreaks of equal severity.
Often, as outbreaks become more frequent, severity tends to decrease, decreasing the benefits of vaccination. The benefits of vaccination are also larger if an outbreak occurs in years of high prices. Further, there will likely be a lot of stress and emotional costs associated with an outbreak that are not included in these results.