by George Looby
Dairy farmers have a long history of dealing with a wide variety of problems that have made their already difficult jobs a little more challenging. When one problem has been addressed, another surfaces to take its place. As Gilda Radner was fond of saying, “It’s always something.”
Twenty years ago the incidence of infections in dairy herds attributed to an organism called Salmonella Dublin was rather uncommon, but today the number of reported cases is on the rise. Salmonella Dublin can cause a variety of conditions in cattle but has the potential to cause infections in humans as well. This has raised concerns in the regulatory areas to monitor reports of this infection in dairy herds. There are many reasons not to drink raw milk and this may be one of them.
Once established in a herd it is difficult, if not impossible, to eliminate. Infected cows may become carriers, showing no symptoms, and shed the organism intermittently in manure. Although spread through the manure is the most common route of dispersal, it can also be spread through colostrum, milk and (in the case of males) semen. Of all the multiple varieties of Salmonella in the environment it seems that Salmonella Dublin is host adapted to cattle, making its control even more difficult. Of those calves that do not die from the infection, a number will become carriers for life, shedding the organism intermittently. In calves the most common symptom is diarrhea, which is considered generally treatable with a number of antibiotics. Pneumonia probably is the second most common disease caused by these bacteria.
When this bug was first identified as a problem, most of the cases were in California, where about 20 percent of the herds were found to be infected but just 5 percent of the cows. Today it is the most common serotype of Salmonella isolated in diagnostic labs throughout the country.
It is easy to set guidelines to manage the disease if it gains a foothold in any given herd; it’s harder to follow them once the organism settles in. Most operations don’t have the luxury of unlimited space in which to segregate known infected animals so each farm must make do with the facilities they have available.
Isolation of known infected animals is one of the key elements of any control program. Because all infected animals are shedders it is critical they be segregated from known healthy cows. Identifying the shedders becomes the trick. Thorough cleaning and disinfection of calving pens should be at the top of the list of priorities. A vaccination program should be implemented. The problem with present vaccines is that laboratory tests cannot at this time differentiate between a vaccination titer and one due to infection. Calves born to known infected dams should be taken from them immediately after birth to ensure they do not suckle. One approach to the colostrum issue is to pasteurize it and feed it during that critical immediate postpartum period. If this approach is not feasible an alternative means of providing colostrum must be developed. The activities of other carrier species such as dogs, cats, rodents, birds, raccoons and others must be controlled.