Salmonellosis in adult dairy cattle (Proceedings)
Salmonellosis has always been present within the US dairy and beef industries but has become an increasing problem on some dairies due to a variety of factors likely related to increasing herd size, production levels, and increased use of confinement housing. There is little doubt from several studies that the prevalence has increased in this country over the last 10-20 years. Of particular relevance is the increasing prevalence of the host adapted serotype, Salmonella Dublin that can readily adapt into the carrier state in cattle.
Numerous factors have been examined as potential risks for Salmonella prevalence in some large, multi-state studies, and it appears that larger herd size is one of the more repeatable factors. Biosecurity is a bigger challenge for larger dairies when compared to smaller herds due to housing systems, the frequent need to purchase animals or at least raise heifers off site, and the inevitable exposure risks for what is a fecal-orally transmitted disease. There is an increased potential for exposure within housing, in the parlor, or in other areas that cattle are located. Cattle around the time of calving are more immunologically susceptible to new infections and sick, lame and older cattle are more likely to be shedding Salmonella without necessarily showing typical signs, hence designing and managing cattle with these facts in mind can be helpful in prevention.
Risk factors for salmonella• More frequent in dairy herds than beef herds, mixed dairy and beef herds and calf herds.
• Outbreaks more common in calving season, and also appear to be more common in the summer months.
• Outbreaks more common in large herds.
• Purchasing cattle from "dealers" rather than source herds.
• Sick and calving cows commingled.
• Wild birds having access to feed storage facilities.
• Antimicrobial use prior to or at the time of exposure.
• Use of flush water systems.
• Feeding brewers' products, animal by-pass protein sources, vegetable or other fat sources to lactating cows.
• Allowing commodity storage areas, particularly those that drain poorly or can retain moisture, to become wet.
Losses due to salmonella
Because Salmonella can cause reproductive losses, typically abortion in late pregnancy, and/or diarrhea in cattle of any age, any sudden occurrence of either of these problems in a number of cattle over a short period of time should alert producers to the possibility of disease. Increasingly, we also have concerns over the potential subclinical impact of Salmonella exposure and infection on production and general cow health. Because Salmonella is present in the environment of so many dairies (probably as many as 50% based upon study results), it is inevitable that cattle will be exposed, and even though they may not become clinically ill, the infection may be a sufficient drain on them to lessen production, fertility or resistance to other diseases.
Where does it come from?
On a dairy, the source of the infection is usually feces from infected individuals. It may be difficult to tell which cows are shedding bacteria because asymptomatic and subclinically affected animals can shed as many organisms in their manure as the cows that are sick with salmonellosis. Other sources of infection may be rodents, birds (including waterfowl), flies, feral cats, dogs, raccoons and, rarely, people – although collectively these likely represent a much less significant source of infectious risk than cattle. Even on farms where there is no active clinical disease or recent history of Salmonella type illness studies show that it is very easy to find Salmonella organisms within the environment and many housing areas.
• Fecal – oral transmission
Salmonella spp. infection occurs when a susceptible animal ingests the bacteria. Adult dairy cattle most commonly ingest feed or water that has been contaminated with feces from animals shedding the organism, whereas calves may consume infected colostrum, milk or even inhale the organism in aerosols. Salmonellosis has a wide spectrum of manifestations in cattle. Asymptomatic, mild clinical or fulminant bacteremia/septicemia and endotoxemic infections can occur.