Bovine viral diarrhoea (BVD) is not beaten yet. Animal Health Ireland (AHI) data confirms that 644 BVD-positive calves were detected in 2025.
Encouragingly, the latest programme results from 2026 show some optimism. As of week 11 of 2026 (18/03/2026), BVD-positive cases stands at 139, compared with 219 for week 12 of 2025 (19/03/2025).
However, this progress is fragile, and farmers must not become complacent.
A critical consequence of the programme’s success is the growth of naive herds nationwide. If BVD enters a herd today, the consequences can be devastating.
Risk of infection
With lower prevalence of BVD circulating, many herds are unvaccinated. This growing naivety means a single persistently infected (PI) calf can now cause an outbreak on a scale which we have not seen in years.
‘’In this practice, we have seen more BVD in the previous three years than in the six or seven years before that. It is a ticking time bomb if BVD gets into a herd.
There are only around 200 positive herds now, down from 11% of breeding herds in 2012, but 13 years in, it should be eradicated.
"The Department and all the stakeholders need to step up at this stage. Yes, farmers should be encouraged to test their calves more quickly. But there must also be adequate compensation for positive calves and it is imperative that funding is provided to vaccinate all breeding animals in outbreak areas,’’ said John Berkery, Mulcair Veterinary, Newport, Co Tipperary.
John Berkery, Mulcair Veterinary, Newport, Co. Tipperary
PI and TI animals
Understanding the difference between persistently infected (PI) and transiently infected (TI) animals is important.
A PI animal is a calf born to a dam infected with BVD during pregnancy. A TI animal is infected after birth. While a TI animal can clear the virus, it sheds the virus for approximately three weeks and is likely immunosuppressed, making it vulnerable to secondary infections. This is how the virus spreads in herds and why rapid detection is critical.
‘’Tag the calf as early as possible and get the samples to the lab without delay. Once the calf is dry, tag it. Samples should be going to the lab at least two or three times a week,’’ advises Michael Daly, Buttevant Veterinary Centre, Co Cork.
Michael Daly, Buttevant Veterinary Centre, Co. Cork.
Multiple avenues of infection
One of the most dangerous traits of the virus is its ability to remain silent. Reduced conception rates, poor calf performance and increased respiratory disease, but none of these exclusively signal BVD without testing.
The threat does not only come from within the farm gate; neighbouring herds, mixing of cattle at marts, purchased livestock, transport equipment and personnel can all introduce the virus.
‘’We are still seeing two or three new PI cases every year due to naive herds and reduced vaccination. When there is less disease around, people tend to lower their guard. Our advice is to vaccinate, buy from known sources, keep informed about your area and the area you are buying from, and always quarantine incoming animals,’’ said Joaquim Canotiho, Ormonde Veterinary Hospital, Kilkenny.
Joaquim Canotiho, Ormonde Veterinary Hospital, Kilkenny
Checking AHI’s monthly programme maps before purchasing livestock is a useful guide worth taking advantage of. Awareness of a herd's BVD status can be the difference between a safe purchase and an outbreak.
Importance of vaccinating
With BVD still circulating, vaccination remains a key pillar of herd protection, particularly for breeding females. Bovilis BVD from MSD Animal Health protects the foetus against transplacental infection with BVD. The primary course consists of two injections four weeks apart, followed by booster before next breeding, at intervals no greater than 12 months. The final dose or booster must be completed at least four weeks before breeding begins.
‘’Before last year, very few herds were vaccinating. We are advising vaccination now to protect next year’s calves. Especially if a neighbour has had a positive case, definitely vaccinate. Ideally, cows should be fully vaccinated four weeks before breeding starts," said Aidan O’Connell, Shannonside Veterinary, Kilrush, Co Clare.
Aidan O’Connell, Shannonside Veterinary, Kilrush, Co. Clare.
If a positive result is confirmed, vaccinating all breeding females and bulls aged 12 months or older is now mandatory. This is completed under veterinary supervision and funded by the Department of Agriculture, Food and Marine.
Case study: outbreak on an Irish farm
A 100-cow herd in Co Clare bought six in-calf heifers in early 2025; four of the calves born were PI. These four PI calves were confirmed by late February 2025.
After a four-week circuit breaker, all animals were blood tested and 80 animals in the herd tested positive for BVD virus. They had picked up the virus from the PI calves and were transiently infected.
In total, 60 animals in the herd were lost (died or euthanased on humane grounds) due to various diseases as a result of the underlying immunosuppresive effects of the virus, a financially and mentally devastating outcome for the business.
‘’PI animals are virus factories. PI calves pump out massive amounts of the virus. That case opened our eyes. You assume BVD is gone and then this explosion hits," said Aidan O’Connell, Shannonside Veterinary, Kilrush, Co Clare.
Bovine viral diarrhoea (BVD) is not beaten yet. Animal Health Ireland (AHI) data confirms that 644 BVD-positive calves were detected in 2025.
Encouragingly, the latest programme results from 2026 show some optimism. As of week 11 of 2026 (18/03/2026), BVD-positive cases stands at 139, compared with 219 for week 12 of 2025 (19/03/2025).
However, this progress is fragile, and farmers must not become complacent.
A critical consequence of the programme’s success is the growth of naive herds nationwide. If BVD enters a herd today, the consequences can be devastating.
Risk of infection
With lower prevalence of BVD circulating, many herds are unvaccinated. This growing naivety means a single persistently infected (PI) calf can now cause an outbreak on a scale which we have not seen in years.
‘’In this practice, we have seen more BVD in the previous three years than in the six or seven years before that. It is a ticking time bomb if BVD gets into a herd.
There are only around 200 positive herds now, down from 11% of breeding herds in 2012, but 13 years in, it should be eradicated.
"The Department and all the stakeholders need to step up at this stage. Yes, farmers should be encouraged to test their calves more quickly. But there must also be adequate compensation for positive calves and it is imperative that funding is provided to vaccinate all breeding animals in outbreak areas,’’ said John Berkery, Mulcair Veterinary, Newport, Co Tipperary.
John Berkery, Mulcair Veterinary, Newport, Co. Tipperary
PI and TI animals
Understanding the difference between persistently infected (PI) and transiently infected (TI) animals is important.
A PI animal is a calf born to a dam infected with BVD during pregnancy. A TI animal is infected after birth. While a TI animal can clear the virus, it sheds the virus for approximately three weeks and is likely immunosuppressed, making it vulnerable to secondary infections. This is how the virus spreads in herds and why rapid detection is critical.
‘’Tag the calf as early as possible and get the samples to the lab without delay. Once the calf is dry, tag it. Samples should be going to the lab at least two or three times a week,’’ advises Michael Daly, Buttevant Veterinary Centre, Co Cork.
Michael Daly, Buttevant Veterinary Centre, Co. Cork.
Multiple avenues of infection
One of the most dangerous traits of the virus is its ability to remain silent. Reduced conception rates, poor calf performance and increased respiratory disease, but none of these exclusively signal BVD without testing.
The threat does not only come from within the farm gate; neighbouring herds, mixing of cattle at marts, purchased livestock, transport equipment and personnel can all introduce the virus.
‘’We are still seeing two or three new PI cases every year due to naive herds and reduced vaccination. When there is less disease around, people tend to lower their guard. Our advice is to vaccinate, buy from known sources, keep informed about your area and the area you are buying from, and always quarantine incoming animals,’’ said Joaquim Canotiho, Ormonde Veterinary Hospital, Kilkenny.
Joaquim Canotiho, Ormonde Veterinary Hospital, Kilkenny
Checking AHI’s monthly programme maps before purchasing livestock is a useful guide worth taking advantage of. Awareness of a herd's BVD status can be the difference between a safe purchase and an outbreak.
Importance of vaccinating
With BVD still circulating, vaccination remains a key pillar of herd protection, particularly for breeding females. Bovilis BVD from MSD Animal Health protects the foetus against transplacental infection with BVD. The primary course consists of two injections four weeks apart, followed by booster before next breeding, at intervals no greater than 12 months. The final dose or booster must be completed at least four weeks before breeding begins.
‘’Before last year, very few herds were vaccinating. We are advising vaccination now to protect next year’s calves. Especially if a neighbour has had a positive case, definitely vaccinate. Ideally, cows should be fully vaccinated four weeks before breeding starts," said Aidan O’Connell, Shannonside Veterinary, Kilrush, Co Clare.
Aidan O’Connell, Shannonside Veterinary, Kilrush, Co. Clare.
If a positive result is confirmed, vaccinating all breeding females and bulls aged 12 months or older is now mandatory. This is completed under veterinary supervision and funded by the Department of Agriculture, Food and Marine.
Case study: outbreak on an Irish farm
A 100-cow herd in Co Clare bought six in-calf heifers in early 2025; four of the calves born were PI. These four PI calves were confirmed by late February 2025.
After a four-week circuit breaker, all animals were blood tested and 80 animals in the herd tested positive for BVD virus. They had picked up the virus from the PI calves and were transiently infected.
In total, 60 animals in the herd were lost (died or euthanased on humane grounds) due to various diseases as a result of the underlying immunosuppresive effects of the virus, a financially and mentally devastating outcome for the business.
‘’PI animals are virus factories. PI calves pump out massive amounts of the virus. That case opened our eyes. You assume BVD is gone and then this explosion hits," said Aidan O’Connell, Shannonside Veterinary, Kilrush, Co Clare.
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