This study evaluated the effectiveness of ivermectin in treating gastrointestinal nematode infections in first grazing season dairy calves on nine farms in County Kilkenny, Ireland. Faecal egg count reduction tests found ivermectin resistance in nematodes on all nine farms, with egg count reductions below the 95% threshold level. Questionnaires revealed farmers did not use faecal egg counting to determine need for anthelmintic treatment. The findings highlight the need for Irish dairy farmers to re-evaluate nematode control practices and use more judicious, evidence-based anthelmintic treatment guided by routine faecal egg counting.

1. Failure of Ivermectin to Control Nematode
Challenge on Nine Irish Dairy Farms
Conclusion
The detection of ivermectin-resistant nematodes on all farms in this study highlights the need
for Irish dairy farmers to re-evaluate their nematode control practices.
Introduction
Increasing reports of anthelmintic resistance in cattle has precipitated the need to establish the effectiveness of commonly used
anthelmintics on cattle farms. The faecal egg count reduction test (FECRT) is the standard method for monitoring the performance of
anthelmintics for the treatment of gastrointestinal nematode (GIN) infections.
Objective
To evaluate the performance of Ivermectin in treating GIN infections in first grazing season (FGS) dairy calves on nine dairy farms in
Co. Kilkenny using a FECRT.
Materials and methods
• Nine dairy farms in Co. Kilkenny with 15 previously untreated FGS dairy calves, which were on pasture for a minimum of six weeks,
were injected subcutaneously with Ivermectin in accordance with their live weights (day 0). Rectal faecal samples were collected from
calves on day 0 and on day 14.
• Faecal egg counts were determined using the Mini-FLOTAC technique (limit of detection of five eggs per gram of faeces (epg)).
• A questionnaire captured details of typical parasite dosing practices and grazing management for FSG calves on each farm.
Results
• All farms had FEC reductions below the 95% threshold level with the lower confidence interval
ranging from 0.2 - 72.8%.
• The mean (arithmetic) FEC on day 0 did not exceed 100 epg on any farm.
• None of the farmers had previously used faecal egg counting as a guide to determine the need for
anthelmintic treatment of calves.
Yvonne Drought1, James O’Shaughnessy2, John Lynch3, Marian Denny4 ,Christine Hurley4 and Maresa Sheehan4
1School of Veterinary Medicine, University College Dublin
2Veterinary Public Health Regulatory Laboratory, Department of Agriculture, Food and the Marine, Backweston Laboratory Campus, Celbridge, Co. Kildare
3 Archersfield Veterinary Clinic, Kilkenny
4Regional Veterinary Laboratories Division, Department of Agriculture, Food and the Marine
Statistical
analysis
Data were
analysed
using the
‘eggCounts’
package
(http://shiny.m
ath.uzh.ch/us
er/furrer/shiny
as/shiny-
eggCounts/).
Discussion
• Second report of ivermectin resistant cattle nematodes in Ireland.
• The FECRT revealed the presence of Ivermectin-resistant nematodes on all farms.
• The low numbers of strongyle eggs recovered from calf faecal samples pre-dosing, highlights that the use of anthelmintic
treatments should be guided by routine FEC monitoring and more judicious, evidence-based use of anthelmintics.
Fig.1 Mini-FLOTAC
(http://www.parassitologia.unina.it/flotac/
mini-flotac/)
Fig.2 Strongyle egg (left) and Nematodirus
egg (right)
The author would like to acknowledge and thank the nine farmers who participated
in the study, the DAFM for financial assistance in completing this project and
the staff in the Kilkenny Regional Veterinary Laboratory for their continued support.
150 μm
75μm