Salmonella in Cattle

Last spring there was wide spread discussion following a severe Salmonella epidemic in a Manawatu dairy herd.

While the size of this epidemic was unusual, the annual occurrence of Salmonella outbreaks is common particularly in spring calving herds when a cow is at its most susceptible late in pregnancy or in the month or two after calving.

Salmonella bacteria are widespread both in bird life and animals and carrier states exist i.e. given the right conditions, clinical disease will follow.

In ruminants, the critical factor is the creation of conditions that lead to a slowing of gut motility. As part of normal rumen function the bacteria & protozoa produce volatile fatty acids (VFAs) which the risk of developing Salmonellosis.

When is an outbreak most likely to occur?  Around calving, as we go through the transition from late pregnancy through calving and into the first month or two of lactation.

In recent years concern has been raised over Mg supplements and whether these are associated with an increased occurrence of Salmonellosis .  The discussion around this is not clear, but comment has been made that the size of Mg granules when too large or not finely milled may lead to digestive upset.

How does salmonellosis present? The first sign can be a sick cow and sudden death.  Typically affected cattle will be obviously sick and there is a severe and bloody diarrhoea often with intestinal lining being passed.  These cases are not pretty.

Treatment of clinical cases can be attempted as long as the disease has not progressed too far.  Routinely we use lots of fluids pumped into the rumen plus antibiotic cover as well as injections of non-steroidal anti-inflammatories (NSAIDs).  Treatment outcome is often poor with a high death rate in those clinically affected. Separation of the sick cattle from the healthy members of the herd is critical.

Prevention by vaccination is by far the most cost effective way to avoid an outbreak of Salmonellosis; you will only need one epidemic and you will be a convert for life.  We will recommend vaccinating into the face of an outbreak.

Because Salmonella is a Gram-negative bacteria, vaccination for prevention, is best undertaken during the dry period.  Following vaccination, an elevated temperature for a day or so is common and if the cow is milking you may see production temporarily drop.

The vaccine is not expensive (around $1 per vaccination per cow) with two shots required initially and an annual booster thereafter.

Most of the cases involve Salmonella typhimurium and these bacteria will cause disease in humans; the disease is highly contagious.  Never drink unpasteurised milk from Salmonella infected cows and never feed this milk to calves.

For what can be a devastating disease at a time of the year when time is precious, the solution for avoiding this risk is simple. If you want further advice, please call one of our veterinary team.