Salmonella can be a devastating disease on our farms. You should ask yourself, what’s the risk for my farm? As an exporter of a large amount of our dairy products, it is important we continue to reduce the incidence of this infectious disease in our herds. On a trip to Denmark over the summer, I saw how a 10-year national control programme had dramatically reduced salmonella infections. I always keep an eye on Denmark because it is our main competitor in the baby powder market.

There are two main species of this bacteria affecting Irish herds – salmonella Dublin (85% of reported cases) and S typhimurium (11% of reported cases).

Looking at dairy bulk milk screening tests, there is a suggestion that close to 40% of herds (testing) show some positive readings.

What are the problems?

Most farmers are aware of the risk of salmonella abortions. These can be caused by salmonella Dublin usually between five to eight months of pregnancy.

A lot of these outbreaks may only present as abortions. However, up to 10% to 20% of infected animals in some herds can abort. So, all abortions must be recorded and investigated.

S Dublin can cause other problems in cows. It doesn’t always cause scour, but can cause more unusual symptoms and can be isolated in cases with pneumonia-like symptoms.

We often associate it with bloody diarrhoea, which can be severe, often bloody and smelly. Sometimes you can see the lining of damaged intestine being passed out in faeces.

Salmonella causes severe depression and scour in young dairy calves.

In calves it can also cause a range of symptoms, typically affecting those between two and eight weeks of age. It can cause septicaemia, when the bacteria travels in blood, causing marked depression and sickness. It can also go to the lungs and joints. With some cases of S Dublin you can get abscesses in the neck vertebrae, causing paralysis and death. Sometimes after septicaemia you can have terminal gangrene (tissue at ear, tail and leg tips dying).

Mortality can be high during an outbreak, while calves in the group tend to do quite poorly.

How does it get on to your farm?

The most likely source is animals that have been bought in.

Seemingly healthy animals can become carriers. These carriers can shed the disease (in faeces and milk) when coming under stress, while potentially not showing symptoms. This can be devastating for animals that have not been exposed previously and is often where we see abortion storms in herds.

It is thought salmonella is stored in the gall bladder, the liver and the lymph glands. The liver plays a key role in immunity so when you have liver fluke infestations, salmonella risk increases.

Animals under stress can shed the disease or show symptoms. This is why young calves are particularly at risk. We need to be vigilant at housing time in dairy herds and also around times of a dietary change (this can affect gut flora and salmonella shedding). Any time in the cow’s life where she comes under stress and her immunity drops, like around calving, can be risky.

After an outbreak or infection one symptom can be terminal dry gangrene of the extremities like in the picture above.

The disease can also be spread by birds, rodents, cats and vehicles. Some reports have suggested watercourses carrying the infection from neighbouring herds have also been a source of spread. Salmonella can survive for up to two years in the right conditions, so slurry is also a potential source.

When buying in replacement stock, is salmonella blood testing worth considering?

Spreading animal to animal

This disease is shed mostly in faeces but can be spread in milk from infected animals also. The main way it is spread is by ingesting contaminated faeces orally.

This is complicated by the fact that salmonella can survive so long in the environment in the right conditions (up to two years). This is why infected animals or suspect cases must be isolated quickly to prevent further spread. Most disinfectants will kill salmonella after faecal material has been removed from sheds.

As salmonella can be contracted by humans, great care and personal hygiene should be taken when dealing with suspected cases.

With feed being a potential source if contaminated, it is so important to ensure all feed stores are tightly locked up.

How can I assess risk?

No farm is risk free. A healthy herd with minimal stress that is closed gives you the best chance possible. In rapidly expanding herds, salmonella is one of the biggest disease risks. So farms where feeding is tight or extra stock is being carried into the winter should really think about salmonella control now.

How can I find out my herd status?

One of the simple monitoring tools is bulk milk testing. This can measure bulk milk antibodies for salmonella. If they are present, you should talk to your vet about risks and control plans. In some farms, blood testing six to eight yearlings to look for antibodies is an option. My top tip is to monitor your bulk milk salmonella antibody levels very carefully and ask for advice if they ever increase.

How do I treat cases?

S Dublin abortion rarely requires treatment but cows should be carefully monitored after any abortion and foetuses should be submitted for testing. With calf septicaemia I always found aggressive fluid treatments being the main benefit. Injectable antibiotics are also very important where septicaemia is suspected.

The use of oral antibiotics is under debate still as regards how effective they are for salmonella scours. The use of anti-inflammatories in all cases has been shown to have significant benefit.

Cows with septicaemia and scours also benefit from having fluid losses addressed. Injectable antibiotics should be used if blood-borne infections are present and consult your vet with regards to oral treatments. Remember that animals that are infected can shed for months after typhimurium, and there can be lifelong intermittent shedding (at times of stress) with S Dublin. In the short term, always try to isolate these sick animals.

Vaccination

There is one vaccine on the Irish market for salmonella. It must be considered in any control programme on farms with suspicion of salmonella.

This vaccination timing is critical. If preventing abortions, most farms will administer in August or September. If there are issues around scours in freshly calved cows or calf scour then there is some benefit to giving at the start of the dry period. I have tried vaccinating calves but found vaccinating cows and maximising passive transfer to be the best option with colostrum.

Hygiene and biosecurity

This is an area where we can really help with keeping salmonella out and stopping its spread within a farm. Consider blood-testing animals coming in and always remove quickly any cows or calves showing symptoms as described above. Remember, bacteria can survive a long time in the environment and thorough cleaning and disinfection is essential between batches and in calving pens.

Stress

Reducing stress on cows can have a huge positive impact. Key to this is managing winter feeding, particularly around housing and the all-important transition period for the dairy cow. Provide adequate space for cows and minimise faeces build-up.

Salmonella is one of these diseases that, after an outbreak, farmers wish they acted earlier to reduce their risk. Your choice, but prevention beats cure on this one.