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Dairy Cattle Health Updates, Advice and Tips from Devoted Vets

Warning! Local conditions are right for Salmonella outbreaks in dairy herds in West Gippsland

The very wet conditions at the start of calving are similar to those seen in 1995/6 when the district was plagued by Salmonella outbreaks in herds of milking cows.

Salmonella is a bacterial disease that causes severe watery, bloody diarrhoea in cattle and other species including humans.

The internal lining of the bowel is stripped away by the infection, and shreds of bowel lining can be seen in the diarrhoea. This loss of lining opens up the cows general circulation to bacteria from the bowel, which are then able to invade the bloodstream. This causes potentially fatal shock and blood poisoning. In addition, the bowel loses water and electrolytes causing a potentially fatal dehydration.

The signs of Salmonella are initially a sudden depression, loss of appetite, marked reduction in milk production and a temperature. These signs may be seen before the start of the diarrhoea. The diarrhoea, as mentioned earlier is watery, bloody and often contains strips of bowel lining. This may be mixed with normal manure, or the appearance of normal manure is completely lost.

Severe dehydration, increasing depression and shock follow. The dehydration is best indicated by a sinking of the eyeball, back into its socket. This "sinking" can range from just noticable to severe. Death can occur within 24 hours.

Salmonella is caught by cows (or calves) eating contaminated food or water. Contamination can be caused by other cows with clinical Salmonella, or by apparently normal cows "shedding" bacteria in their manure during times of stress such as calving and cold weather, or by rats and mice, or by wild birdlife such as ducks and ibis. Typically, infected or carrier cows contaminate pasture, rats and mice contaminated grain and concentrates, and wild birds contaminate pasture and water. Unfortunately it is impossible to eliminate the risk of Salmonella contamination on a farm. Disease occurs when the "dose" of bacteria taken in by a susceptible cow or calf is so high that it overwhelms the animal's immunity.

Treatment of individual sick animals consists of antibiotics, antiinflammatory pain relief, and fluid replacement treatment when required. Without the benefit of manure testing to help determine choice of antibiotic, our initial recommendation is trisoprim 480, and support with either flunixon or meloxicam 20 as an anti-shock pain reliever.

The quantity of fluids required for rehydration is massive, for example 25-30 lts of warm water plus electrolytes. Fluids are usually given via stomach tube, and if this is required, call one of our vets to help.

Vaccination is the main form of prevention. The vaccine contains the two most common types of Salmonella - Salmonella typhimurium and Salmonella dublin. It is a two ml dose given under skin, high up on the neck behind the ear. Two initial doses should be given to cows with an interval of 3 to 4 weeks apart. A booster dose is given annually.

Because Salmonella is also a serious disease of calves, a vaccination program can be set up for dry cows, with the calves receiving immunity in the colostrum. Calves can then be vaccinated at 8 and 12 weeks.

At the start of an outbreak, it is important to sample the manure/diarrhoea of affected cows and submit it for bacterial identification. There are a large number of types of Salmonella of which S. dublin and S. typhimurium are the most common two. A vaccination program may not protect against other types of Salmonella, and so early identification can be useful in determining the effectiveness of a vaccination program.

Vaccines can also be custom made for specific types of Salmonella, but there is a significant time delay between the first case, identification of the type, and manufacture of the vaccine. Often the outbreak is over by the time the vaccine is ready. As the vaccine contains only S. dublin or S. typhimurium, if you know you are dealing with either of these types, then there is no delay beyond waiting for the lab result.

Salmonella typhimurium is often associated with rats and mice as a source, so rodent control of grain and concentrate food sources becomes an issue.

For calves, the cleanliness of calving areas and calf pen bedding is important.

Salmonella also infects humans and causes serious disease, so from an Occupational Health and Safety issue, it is important to call a veterinarian on farm for confirmation of the disease, and implementation of a treatment and control program to suit your own farm.

Key points:

  • Be alert for cows with sudden drops in production - take temperatures and collect a manure sample with a rectal glove.
  • Call one of our Devoted Vets immediately if Salmonella is suspected.
  • Immediately treat with Trisoprim 480 in the muscle.
  • Submit the manure for testing.
  • Under the current wet and cold conditions, we strongly recommend vaccination of all cows, either before or after calving.

Contact Devoted Vets on 03 5623 2525 for more information regarding Salmonella, treatment and prevention. Devoted Vets at Warragul Vet Clinic for dairy farmers in West Gippsland.