Salmonella risk in dairy herds begins to peak over the autumn
Published 21/09/2016 | 02:30
Before I started this article, I quickly opened my emails to see a lab result from an aborted calf we had sent in to be tested.
It had come back as positive for salmonella Dublin and this was the cause of the abortion. This is the second case I have identified in the last six weeks. It is not surprising, as autumn time tends to see the beginning of the peak risk time for salmonella abortions.
I also have had a huge amount of questions from dairy clients recently about positive results on their bulk milk screening tests for salmonella. Questions about how worried should they be and should they vaccinate their cows. This is a discussion each farmer must have with their own vet and decide based on risk about vaccination. Where it has been diagnosed on an abortion there is no discussion the vaccine must be used.
Salmonella is a significant disease in Irish dairy farms, and testing indicates it has a high prevalence - meaning it has been identified in a number of herds even though they aren't showing any clinical signs.
The reality, in practice, for me has been the number one disease I have seen associated with the infection in adult cows is abortion caused by a species of salmonella Dublin.
Followed by some herds getting enteritis or scours often caused by S.Dublin or on some occasions S.thphimurium. In calves it tends to cause septicaemias, which can present as calves with high temperatures being sick stiff and sore.
It can also cause scour in calves and a number of other conditions. So, the big question for farmers is 'I have none of these signs at the moment but my bulk screening test says I have salmonella positive antibodies'.
It can be confusing and I have to admit for many farmers frightening that this disease might be lurking in the herd. So to answer the question I have to explain what the test means.
A positive result means that there is evidence that some portion of your cows have encountered salmonella species and have created antibodies against them. This current test does not distinguish which species is in the herd but it can be used as an early warning sign.
So, to understand the significance of this test, we then need to look at how salmonella spreads in herds.
Cows that are infected with salmonella will often appear clinically normal and healthy, however they are carriers of the bacteria. What happens these animals at times of stress is they can begin shedding the bacteria infecting other cows or getting sick themselves. It is no wonder then, in rapidly expanding herds, this is one of the diseases that often causes problems.
Salmonella loves stressed cows under pressure and rapidly expanding herds will often meet the bugs' terms and conditions.
There is also more options around testing with further PCR tests on milk that can be used.
Blood tests can also be used but would prove expensive to run on a whole-herd basis. For me also, it is so important to send any aborted calves to the lab as it dramatically increases the chance of a diagnosis.
The problem for many farmers now is that they know they have some evidence of the disease in healthy cattle and their only option seems to be another expensive vaccine.
Knowing what I know about the disease I can only offer advice to vaccinate where I see a positive result on the bulk milk. I will often for those unsure, offer the option to talk to farmers who have experienced abortion storms or scour outbreaks in calves. Their experience will be to not take the risk.
It can be a devastating disease and the vaccination does present an option for controlling the disease. From my experience, like all vaccinations, timing is critical. Ensuring the vaccine is given pre the risk time, guarantees that the cows have maximum immunity against the disease when they need it. So talk to your vet about salmonella and timing of vaccination for your herd.
One other critical thing I have seen with salmonella is its link to fluke infestations. Fluke affects the liver and adult fluke reside in the gall bladder.
Salmonella carrier cows also have salmonella in the gallbladder so, often where you see fluke and salmonella present you can see a significant increase in the disease.
Just another reason for farms to have a stringent liver fluke control program.
It is also worth remembering of course that it can be spread to humans and great care should be taken handling suspect cases, cows and abortions. For those closed herds and herds that do not have any evidence of infection it is so important to keep the disease out!
The main risk factors for transmission are bought in stock (carriers) and infected animals.
It is also advisable to have a strict biosecurity plan in place to keep the disease out.
I was asked recently by a farmer who said to me 'there was none of this crack years ago why the hell do I need all these expensive vaccines now?'
My answer to him was that our modern herds are different and we face many challenges. I never promote vaccines as a silver bullet but an aid where necessary to remove the risk of disease.
Good husbandry and nutrition are still the backbone of a healthy herd. However, with expanding herds and more animal movement than ever we are playing into to the hands of these infectious diseases.
Vaccines are an aid along with good herd health planning to minimise the risk.
He probably left unhappy but did agree the modern cow and farmer, for that matter, have a more stressful existence.
Tommy Heffernan is a Co Wicklow-based vet email: firstname.lastname@example.org