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Salmonella in Dairy Cattle

By Dr. Curt Vlietstra

Salmonella in dairy cattle can be a devastating disease in cows and calves of any age or stage of production.  Treatment is difficult, and protection from vaccines is no guarantee, which makes this one of the more frustrating diseases for farmers and veterinarians to deal with.  Salmonella can certainly be an important disease in beef cattle as well, but it is far less common.

The hallmark signs of Salmonella are a high fever and diarrhea.  There are often remnants of sloughed-off intestinal linings in the feces, and the feces may tend to be watery and yellow-colored with a putrid odor.  Survivors of the initial infection may be prone to disease in other organ systems that is difficult to treat, including the brain, lungs, and kidneys.

For the purposes of this discussion, I will split the topic into two parts: Young calves, and then all other dairy cattle.

Salmonella in Dairy Youngstock

The primary route of transmission for Salmonella is fecal-oral.  This means that, except for rare cases that I will discuss later, the way that a calf gets exposed to Salmonella is for feces with Salmonella organisms to be ingested by a calf in a dose high enough to cause disease.  Because there is so much variation between Salmonella organisms, strains, subtypes, etc, with some having a very low infectious dose and others much higher, it is safest to assume that any fecal contamination of the calving pen (including cows if calves are left with mothers long enough to stand and suckle), young calf feeding equipment, carts or trailers used to transport young calves, boots, and feed (including non-pasteurized waste milk) can lead to sick calves.

The most common Salmonella vaccines are meant to minimize shedding of the cows in the herd and reduce the exposure levels in calving pens.  Some attempts have been made to vaccinate very young calves with commercial vaccines or by using vaccines off-label.  These practices carry risks including vaccine reactions and inefficacy, but may be recommended in herds with an extremely high prevalence.

Salmonella bacteria have an amazing ability to adapt and survive.  Many types can evade the immune system once they pass through the gut wall, leading to chronic poor-doing calves that may shed during periods of stress and expose pen-mates.  Additionally, Salmonella organisms are often resistant to most antibiotics.  When dealing with a case that makes you suspicious of Salmonella, treatment should coincide with laboratory confirmation and results as blanket treatment with an ineffective antibiotic can worsen the problem by killing off other gut flora that may be competing with Salmonella but are harmless to the host.

Salmonella in Growing Heifers, Springers, and Cows

Salmonella breaks in older dairy cattle typically involves stressful events or massive exposure.  Birds, especially starlings and pigeons, are very efficient multipliers and shedders of Salmonella.  There propensity to defecate in feeding areas and feed storage areas on dairies makes them a considerable risk factor in Salmonella transmission.  Being careless with equipment that comes in contact with feed is also another means of over-exposure.  Tractors that drive through slurry before entering feed alleys and loader buckets that scoop manure being used to scrape away refusal feed are commonly seen violators.

Once a calf grows to become a functional ruminant, they have the best protection against Salmonella built-in.  The VFA’s (volatile fatty acids) produced in the rumen during normal feed digestion are toxic to even the most antibiotic-resistant types of Salmonella.  Salmonella breaks in these animals are often centered around stressful events because stress reduces feed intake, which decreases VFA production, which reduces the animal’s homemade Salmonella killing machine.

Summary

Animals that are in the acute stage of Salmonella disease may shed bacteria in their saliva, nasal secretions, and milk in addition to their feces.  Because of this, colostrum taken from any suspicious animals should not be used for calves, and animals with very high fevers and diarrhea should be isolated from the rest of the herd if possible.

Even though there are strains of Salmonella that commercial vaccines are not effective against, the disease is significant enough to strongly consider vaccinating to provide whatever protection available.  Because vaccines and antibiotics may not be effective in preventing or treating Salmonella, management practices to prevent exposure are very important.  Pasteurizing waste milk, sanitizing calf feeding equipment, boot washes, bird control, and dedicated equipment used for handling feed are all means of reducing exposure on dairies.

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