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Salmonellosis

Axel de Zeeuw, Veterinarian
In the last couple of months we have been confronted with a number of Salmonella outbreaks on dairy farms.The first things farmers have noticed were very sick cows with watery diarrhoea occasionally with blood (black) and pieces of the intestinal wall present. These cows usually have a high temperature and rapidly deteriorate, become dehydrated and can die very quickly. These cows are the typical Salmonella animals but luckily not all infected cows show these severe signs and some cows might not even show any clinical abnormalities but a big drop in milk production is frequently noted.

Sick animals are usually treated with antibiotics either oxytetracycline (Engemycine®) or trimethoprim-sulphonamides (Amphoprim®) and anti-inflammatories (ie Ketofen® Metacam®). Severely dehydrated cows should be supported with (intravenous) fluids. Another aid is vaccination of the herd during an outbreak, vaccination does not prevent further spreading in these situations but does reduce the severity of the disease. Unvaccinated animals should be vaccinated twice 4 weeks apart and then boostered annually, this aid in the control of the disease is a cheap ($1.30/cow) and easy option and doesn't need to be done by a vet. The most commonly found types of Samonella in New Zealand are S. Typhimurium and S. Bovismorbificans, both types we have diagnosed recently and are covered in the vaccine.

Spreading of the disease is normally by faecal-oral route and sick animals are shedding large amounts of the bacteria, ideally effluent should not be spread onto grazing paddocks or at least not be grazed for 4-5 weeks.

Why we did see these outbreaks this year is not a straightforward answer and we believe Salmonellosis is a multi-factorial disease. We know the bacteria can survive in soils and water for months, the wet conditions this year have likely contributed to the spreading.Other risk factors include birds and rodents which can contribute to the spreading and in general stress such as calving, diet changes, overcrowding and other diseases. A risk factor that was proposed a few years ago is feeding large particle magnesium-oxide, the exact reason behind this is not really clear.

Last thing to really emphasize once more is personal hygiene as Salmonella is a zoonosis!

If you have any concern regarding Salmonella in your herd please talk to your vet.