A collection of over 100 vets from all four corners of the country descended on Newpark Hotel in Kilkenny last week for DairyCon, a two-day conference aimed at vets operating in dairy farm practices.
The event, run by FarmLab Diagnostics, discussed some of the latest updates on infectious diseases, herd health and nutrition for dairy herds.
Vector-borne diseases
The conference opened with a presentation from Ronan O’Neill, head of Virology at the Department of Agriculture, on the growing risk of vector-borne viruses, with bluetongue being the latest example of one such disease.
“A vector-borne disease is a disease with a middle-man. It’s not just a case of a host and a virus, there’s something in between. This makes these diseases highly mobile and it’s no longer a case of animals in shared airspaces being the risk.
“Gates and fences acting as a barrier of prevention no longer works. Sick bays and quarantines aren’t a solution either. The disease will still find its way into the main herd via the vector,” Ronan said.
But why are these vector-borne diseases a greater risk now than ever before? Well, he offered a number of reasons for this.
Climate change plays a big part, while changes to biodiversity as well as globalization of trade and tourism also contribute.
“In terms of the changing climate, average temperature has been rising since the late 1990s. 2024 is the warmest year on record, while 2025 is the third-warmest year on record” Ronan added.
This increase in temperature is the perfect environment for replication of the virus inside the insect, as well as high survival rates of the insects themselves leading to more infected spreaders.
These insects don’t like cold and wet weather with dry weather and temperatures of over 11 degrees Celsius being their optimal environment.
According to Ronan, changes to biodiversity is another factor in the increased risk of vector diseases. Changes to habitats and climate have meant less insect-eating organisms, giving rise to the population of insect species transporting the viruses.
“Of the insect population, the midge is the biggest culprit for transporting viruses in Ireland. This can, however, vary between years. The first of the biting midges this year appeared here on 2 April,” he said.
Just because they were active at this stage doesn’t mean they were infected with viruses like bluetongue, but the risk period begins at that stage.
Bluetongue
Bluetongue is the big talking point at the moment when it comes to vector-borne viruses.
“The vector-borne viruses like bluetongue are what we call RNA viruses. This is important as it means they mutate and move away from various different immunities and possibly even vaccines,” Ronan said.
“They are often transmitted vertically, meaning from mother to baby, and they have multiple serotypes” he continues.
In the case of bluetongue there are over 30 different serotypes and a vaccine for bluetongue serotype-3 won’t protect against bluetongue serotype-8 for example.
Within the serotypes themselves there are different strains such as mild or more severe strains.
Based on all the information out there, it’s evident that bluetongue can’t be avoided. The only thing farms can do is put preventative and management measures in place to deal with the virus.
Pre-existing immunity is one way of reducing the impact of the disease. Animals that are vaccinated or have previously had bluetongue will have immunity built up.
Other factors
Pregnancy, heat stress, housing and body condition score can also exacerbate the effects of the virus.
Taking action where possible to minimise animals’ exposure to factors like heat stress or poor body condition will help to reduce the impact of the virus.
Using needles between infected animals and non-infected animals will spread the virus so, where possible, avoid sharing needles. Bulls are another source of transmission.
Bluetongue can be transferred via semen so vaccinating bulls is important. Bulls that have had bluetongue could also be less fertile, so If there are any fears over a bull that has been sick, fertility test that animal before letting him out with cows.
The majority of animals infected with bluetongue won’t show clinical signs of the disease. The morbidity rate according to Ronan is less than 10%. This would say only one in ten animals with bluetongue, will actually display illness.
In terms of testing for the disease, Ronan explained that it’s ongoing and that the possibility of testing for bluetongue using the ear notches used to sample for BVD has been confirmed.
This is an interesting development that may be useful going forward for the industry.
TB
On the topic of TB, Damien Barrett, head of Ruminant Animal Health at the Department of Agriculture, presented the latest update on TB figures.
There was optimism to be taken from the opening slide of the presentation which outlined falling rates of reactors, herds restricted, herd incidence rates and confirmed slaughter cases over the last 12 months.
“Herd incidence rates are down about 15% on this time last year with reactor numbers falling about 17% and the number of herds restricted down by 1,000” Damien explained.
“The numbers of positive cases we have are primarily coming from the dairy herd. That’s really related to the intensity of production and the number of animals held together and not that there’s a genetic predisposition for TB in dairy cattle.”
According to Damien, due to a lack of detection of the disease in the year of 2022, we’re now playing catch up with TB. He also said that the level of herd incidence fell in 2022, which happened to coincide with record milk prices.
Breakdowns
“Breakdown sizes have increased in herds, which really reflects cattle-to-cattle transmissions and residual infection. Residual infection has assumed a greater importance as herd sizes have increased post-quota.”
Residual infection is the continued presence of TB in a herd despite animals testing positive being culled. In other words, the animals present a false negative and the disease continues to spread.
R-Zero
The R-zero value a measure of the number of animals infected by a single contagious animal.
Based on a study carried out in Co Down by the University of Cambridge, the R-zero value for a badger is one. Every infected badger will therefore infect one animal.
Once the disease gets into a herd of cattle however, it amplifies. The R-zero value in a herd of 30 cattle is around 1.5 but in a herd of 400 cattle the value rises to five.
“In bigger herds of 400 cows that means, one infects five, which infects 25 and then 125 if not detected as early as possible. When not detected early there is a snowball effect” Damien says.
Superspreaders
Superspreaders are having a disproportionate effect on the spread of TB. If the genetic lines of these superspreaders could be identified and eliminated it would make a big difference, according to Damien.
The TB index included in the EBI will have a very positive impact on reducing reactor numbers he added. Selecting the bulls with higher resistance figures is crucial to stop the spread.
“Unfortunately, a vaccination for TB is a bit away and we can’t wait around until it arrives. It will be a game changer if and when it comes but for now, we need to focus on using low-risk bulls and the other measures included in the TB five-point action plan.” he said.
Summer scour syndrome
Kerry-based vet Donal Murphy explored the relatively new topic of summer scour at the conference.
An issue that only reared its head since around 2018, it has quickly become a hot topic on dairy farms and is particularly topical at this time of year.
Calves tend to get it in the month post-turnout according to Donal and can become very ill. The animals affected tend to scour, lose weight and become very sick looking. If the calves are badly affected growth can be stunted and where the issue is not caught in time, they can die.
While there is still no one right answer for what’s causing the problem on farms, Donal says both Irish vets and vets internationally in New Zealand, Australia and England are putting it down to underdeveloped rumens combined with high nitrogen levels in grass.
Offering calves straw or rough grazing and avoiding after grass or paddocks recently fertilised are some of the preventative measures one can take to reduce the risk according to Donal.
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