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Dairy farmers are being warned to keep an eye out for salmonella symptoms in their herds after a sharp rise in diagnoses of the disease on farms over the past two years.
The latest MPI laboratory data shows more than 50 positive samples (cases) of salmonella taken from farms nationwide in 2026 – the same number as last year. In 2024, those cases numbered just five.
It was not known whether each case represented a single or multiple animals – or a whole herd. This made it difficult to determine precisely how many cows had the disease, DairyNZ senior technical and policy advisor (veterinary) Mitch Cooper said.
While there were cases in most of the country’s dairy regions, Taranaki, Bay of Plenty South Canterbury and Otago have seen rises in cases.
The incidence of salmonella on farms has been steadily increasing for over a decade, he said.
“From about 2014 onwards we have seen quite a drastic increase in salmonella.”
The cases are predominantly in adult cows and heifers, and while people love to blame birds for spreading the disease, discovering how it gets onto a farm is more complicated, the former veterinarian said.
“There have been several studies done by Massey University to try to identify the major risk factors – and they have identified some – but I don’t think we are fully at the bottom of where it’s coming from.”
The disease is caused by cows ingesting salmonella bacteria, which can live for long periods of time in the environment (more than six months), making elimination of the organism difficult.
There are a variety of types of salmonella bacteria that can affect dairy cattle. Salmonella typhimurium and Salmonella bovismorbificans are the most common in New Zealand.
It is spread via direct animal-to-animal contact within a herd, other animals or birds, dirty clothing or objects, contaminated feed or water supply, airborne bacteria or the application of untreated effluent to pastures.
Cooper’s advice is to in place good bird and rodent controls around feed and water troughs as that access is a likely scenario for the disease getting onto the property.
Awareness is also key and being mindful of its symptoms. Often it is not until farmers have it in their herd that they pay close attention to it.
“It’s something people don’t put much focus on until it happens to them.”
Symptoms include a drop in milk production, diarrhoea, a loss of appetite, fever, dehydration and in some cases, abortions. It is also more prevalent in spring and autumn.
There is a vaccine for salmonella, which offers protection against four different strains. While not 100% effective, it does significantly reduce the risk, Cooper said.
It can be passed on to humans, presenting a significant health and safety concern for farmers and their staff if the disease is found in the herd.
“I’ve had several veterinary clients that got salmonella from their herds. It’s quite a significant human health issue because it can make you extremely sick.”