A deterioration in the effectiveness of some of the most commonly used animal remedies is spreading at an "alarming" rate, a leading vet has warned.
Doreen Corridan, chief veterinary official at Munster AI, said resistance to many of the top animal treatments has become "a major issue on many farms".
It must be urgently addressed through better animal husbandry "before it gets completely out of control with serious consequences for the sector".
She said that parallel with the anti-microbial resistance (AMR) which is building up in animals, a build up in parasite resistance to commonly used treatments has been widely identified in pasture.
She said that "land resistance to anthelmintic treatments is becoming a big (issue) that is going to be a real problem for many farmers" and cannot be ignored.
A three-year nationwide study - carried out by a team of eight scientists on behalf of the Department of Agriculture involving 4,211 tests on sheep farms - has found that the efficacy of some of the most commonly used anthelmintic treatments has dropped to 31pc.
The average failure rate across the range of commonly used treatments was 49pc.
The report added that it is "imperative that sheep producers know what products are effective on their holdings" and are aware of improvements that need to be made to their control strategies to reduce these issues.
Ms Corridan said it was "very serious" and farmers need to review their systems and look at better housing and nutrition to reduce the need to use the treatments.