Are cattle with BJD likely to be culled for age before they start shedding the bacteria?
Most infected dairy cattle are culled before they break down with obvious disease. However a large proportion of infected cattle do shed bacteria in adult life and can infect calves in the herd. This occurs particularly in infected dairy herds with poor calf management and in infected beef herds with higher stocking rates (especially at calving). Here the degree of effective contact between adults with advanced infection that are shedding high numbers of bacteria and calves is high enough to result in considerable spread. In Canada, beef herds have as much JD as dairy herds, probably due to concentrated winter calving management. Although the grazing management in beef herds in Australia is usually not as intensive as in dairy herds, calves are run with adult cattle for much longer. An introduced infected bull can infect the unweaned calves of cows with which he is joined.