Antimicrobial Resistance: On your MARCS
Type Media Article
John Kilboyle, Teagasc Adviser, Galway/Clare
At this stage of the year, cattle are returning to paddocks that they have already grazed, and parasite burdens will start to develop across farms. Cattle are continuously exposed to parasites such as gastrointestinal nematodes (gut/stomach worms), which compromise animal health, welfare and productivity. Large numbers of worms in the gastrointestinal tract negatively impact feed intake, nutrient use and performance, particularly in young stock. In order to prevent any reduction in performance, it is important to monitor the burdens present. While we do rely on the availability of effective drugs (wormers) to control these pathogens, recent studies have demonstrated that worms are now becoming resistant to the drugs we use to control them (anthelmintic resistance).
Worms are a particular issue in dairy calf-to-beef systems as, due to their age profile, the majority of the animals on the farm have very little immunity to worms. Stomach and lungworm are the main offenders.
Calves are particularly vulnerable to infection from stomach worms, and this can result in ill-thrift and reduced growth rate. After their first grazing season, cattle generally develop sufficient immunity to prevent clinical disease; however, there have been numerous cases where older animals have had high levels of worm burden. Given this, regular monitoring is required in older groups to ensure no issues arise.
Symptoms of stomach worms can include diarrhoea, decreased appetite and loss of weight. Stomach worms can cause severe damage to the stomach and small intestine, which leads to parasitic gastroenteritis.
Regular dung sampling to assess faecal egg counts (FEC) is an excellent way of identifying a worm burden in a group. Where readings in excess of 200 epg (eggs per gram) are recorded, treatment is advisable.
Control of stomach worms
Control of stomach worms is usually achieved by the administration of anthelmintic doses. There are currently three classes of anthelmintic licensed for the control of stomach worms in cattle: benzimidazole (white), levamisole (yellow), and macrocyclic lactone (clear). These products have been highly effective in controlling stomach worm infection in cattle. However, recent studies carried out by Teagasc have shown resistance to all three classes of product. When implementing a dosing strategy, it is good practice to alternate between the different classes of drug to minimise the risk of a potential resistance build-up on farm. Taking a dung sample after treatment is also good practice to ensure the product is effective.
Do you know which wormers are effective against stomach worms in cattle on your farm?
‘Managing Anthelmintic Resistance in Cattle Sustainably’ (MARCS) is a collaborative project between Teagasc, University College Dublin, Queen’s University Belfast, Animal Health Ireland and the Department of Agriculture, Food and the Marine.
The project aims to determine the extent of resistance to wormers on Irish cattle farms, identify major risk factors for the development of resistance so we can target mitigation strategies, and use models of worm populations to apply sustainable parasite control to Irish farms.
As part of the project, we are looking for farms on which to test for wormer resistance. Farmers can participate directly or vets can recruit their clients as participants. The test for resistance is a faecal egg count reduction test (FECRT). This test involves collecting individual faecal samples from a cohort of calves before and after wormer treatment and submitting the samples to the laboratory. A short survey on parasite control practices must also be completed. Full guidance on the testing protocol will be provided and the sample testing will be carried out free of charge. If you are interested in testing for anthelmintic resistance on your farm, contact marcsparasitology@gmail.com.
Lungworm
In the case of lungworm, monitoring for clinical signs such as a husky cough or difficult breathing is the best way to identify if there is an issue. The recent rain after the prolonged dry spell will result in high levels of infestation. Farmers need to be particularly vigilant, as heavy infestations can lead to respiratory disease and so rapid treatment is advised.
As regards treatment and control, most available anthelmintics are effective against larval and adult lungworm. Levamisole and white drenches will eliminate the parasites present on the day of treatment. These classes of dose, however, will have no residual effect and, as a result, shorter treatment intervals will be required. On the other hand, macrocyclic lactones such as ivermectins will provide longer protection.
Best practice when dosing
When administering a drench, particular attention needs to be given to dose-to-weight calculations so animals receive a full dose. Farmers should dose based on the weight of the heaviest animal in the group. Where a large degree of weight variation exists, splitting the group into heavier and lighter sub-groups and dosing based on the heaviest in each is advisable.
When choosing a product, it is important to read the label and instructions carefully to ensure that you know exactly what the dose can and cannot treat. Post-treatment, it is best to dose and return to dirty pasture, as this will help to reduce the development of anthelmintic resistance.
Date for your diary
Sheep 2025, the largest dedicated sheep-focused open day on the island of Ireland, takes place on Saturday, 21st June, from 10am to 5pm at the Teagasc Mellows Campus in Athenry, Co. Galway. Sheep 2025 will offer an unparalleled opportunity for farmers, industry professionals and the general public to explore the latest innovations and trends in the Irish sheep industry.