Economics of Johne's Disease (Proceedings)
Over the last 10 years we have seen a very substantial change in dairy producers' approach to Johne's disease. When the NAHMS dairy '96 survey was conducted, only 18% of producers claimed to be fairly knowledgeable about this problem. Educational efforts to inform producers about the disease have been very successful. The NAHMS dairy 2006 survey shows that 58% of producers are fairly knowledgeable. Considering producers who were either fairly knowledgeable or knew some basics of those surveys showed an improvement from 55% in 1996 to 94% in 2006. This is important progress, because the 2006 survey also showed that on the basis of environmental sampling of dairies at least 68% of US dairies are infected with MAP. This measurement is clearly an underestimate, because the environmental sampling will fail to detect some infected operations. While very few dairies were concerned about Johne's disease in 1996, by 2006 32% of dairy herds were in a control program and 35% were doing some testing.
It seems clear that many veterinarians and producers now have information and tools that can help them work effectively to combat this disease. It is not always clear how aggressively the problem should be pursued and how it ranks in comparison with other issues that producers face. There are numerous disease challenges on dairy operations, some of which have very adverse effects on the cows and are very costly to the operation. It can be difficult to determine which problems should be addressed as the highest priority and what investment of time, effort and money is the most prudent.
A critical determination has not yet been made regarding whether Johne's disease is a zoonotic problem. If it is determined that the causative agent can transfer from cattle to humans and cause Crohn's disease, then this problem warrants very serious attention in order to protect human health. On the other hand, if it does not appear that the agent harms humans, then the primary concern about this disease is its debilitating effect on cattle and resultant economic losses to the herd.The economic impact of this disease in a herd depends greatly on the type of operation. If the owner sells animals from the herd for use as productive cattle on other operations, then the herd should be considered a seedstock operation. In this case Johne's disease is a unique liability because the purchase of new cattle is the primary means of disease introduction into herds. Alternatively, if the producer only sells commercial milk, and if that milk is not seen as a human health risk, then the primary economic impact in the herd is from decreased productivity.
Numerous studies have tried to estimate the economic losses associated with the occurrence of Johne's disease in dairy herds. Although estimates vary widely in the different studies, they are very consistent to identifying the source of economic losses. It appears that the most important loss is from decreased milk production. Reasonable estimates of production loss are that sero-test positive cows show a 10 to 15% lifetime decrease in production. Fecal test positive cows show a three to 30% production loss, with heavy shedders showing the greatest production decreases.
The other major contributors to decreased productivity of cattle with Johne's disease are from increased risk of removal from the herd and from decreased value of the animal at the time of sale. Studies that have evaluated these features have found about a 2 fold increased risk of removal from the herd, with 1 to 3 year decreased productive time in the herd. As the animals are culled, their sale value has been estimated to decrease by 30 to 40% if clinically affected, and sale weight has been estimated as reduced by about 130 lbs if fecal culture positive.
Other liabilities may be attributed to Johne's disease occurrence in a herd, such as increased incidence of other diseases, or decreased reproductive performance or altered milk components. However, these findings have typically not been repeated in other studies, and it seems unlikely that they contribute substantially to the negative effects of the disease.