Dr. Kat Baxter-Smith
Rising infection rates in cattle are prompting a reassessment of lungworm control ahead of turnout this season.
The warning comes as lungworm – once largely confined to youngstock – is now being reported more widely across age groups, raising the stakes for herd health and productivity. New research pointing to the reduced efficacy of macrocyclic lactones has intensified scrutiny of current parasite strategies – particularly in grazing systems that rely heavily on routine treatments. There is also growing evidence of resistance to commonly used wormers. Macrocyclic lactones – including ivermectin and moxidectin – are failing to control lungworm in some herds, according to Glasgow University studies.
The scale of change is significant, says Kat Baxter-Smith, veterinary adviser with MSD Animal Health. “There’s been a tenfold increase in lungworm infections since the mid-1990s – particularly in Scotland and northern England,” she says.
Economic case
Cases of parasitic pneumonia diagnosed and reported to the GB Veterinary Investigation Diagnosis Network rose by 100% across the UK from between 2018 and 2024, says Dr Baxter-Smith.
Incidents are increasingly seen in adult cattle – not just first- or second-season grazers. Lungworm spreads rapidly once cattle ingest larvae from contaminated pasture – and infection then cycles back onto grazing ground.
“Clinical disease in adult cattle can occur late in the season due to a lack of immunity from natural challenge, immunosuppression from other disease – or very high worm burdens,” explains Dr Baxter-Smith.”
Resistance
“This reinforces the need for protection through vaccination.”
Vaccination offers a more sustainable response, argues Dr Baxter-Smith. “Routine use of wormers can encourage resistance as highlighted by recent studies and reduce the animal’s ability to develop natural immunity. Vaccination, however, stimulates immunity through controlled exposure to irradiated larvae, offering long-lasting protection without driving resistance.”
The financial logic is clear. “Outbreaks can cost £50–£100 per affected animal, and up to £3 per head per day in lost milk yield in dairy cows, which is far more costly than vaccinating.”
Farmers are advised to review risk with their vet. “Every farm is different,” says Dr Baxter-Smith.
She added: “A vaccination plan tailored to your farm can help safeguard herd health, reduce financial losses, and protect the efficacy of the wormers we still have.”