During the recent Teagasc Research Insights webinar, which focused on antimicrobial and anthelmintic resistance in farm animals, Orla Keane, a research officer with Teagasc, outlined anti-parasitic resistance (APR) and some of the impacts.
From January 2022, due to changes in EU regulations, farmers and vets will be required to use a more holistic approach to treating animals due to ongoing issues with antimicrobial resistance and APR.
Orla outlined some of the factors that influence the development, and some good practices that can slow the development, of APR.
Internal parasites of ruminants
Anti-parasitic drugs refer to medications that are meant for the purpose of treating various parasitic diseases, such as those caused by parasitic fungi, protozoa, helminths, ectoparasites and amoeba, among many others
Examples of these in agriculture would be for the treatment of coccidia; nematodirus; gutworms; lungworms; and fluke.
APR means that the parasites have the ability to survive doses of drugs that would, otherwise, kill parasites of the same species and growth stage.
Research
Anti-parasitic drugs currently account for 27% of products sold for animal health in Ireland – the largest for any single product.
There are five anthelmintic drugs available for the control of ruminant nematodes on the market currently; three are available over the counter, while two are prescription based.
Class Common name First released First resistance Benzimidazole White (1-BZ) 1961 1964 Levamisole Yellow (2-LV) 1970 1979 Macrocyclic lactone Clear (3-ML) 1981 1988 Amino acetonitrile derivatives Orange (4-AD) 2009 2013 Spiroindoles Purple (5-SI) 2010 2016
During the webinar, Orla outlined some research results collected in 2020, into the prevalence of APR on Irish farms: up to 70% of Irish sheep farms have resistance to benzimidazole, while this figure is 56% on cattle farms.
The figures for Levamisole are: 45% for sheep farms and 17% for cattle farms; while macrocyclic lactone, there was a up to 50% on sheep farms and up to 100% on cattle farms – depending on the product.
Slowing the development of APR
To avoid this from happening, Orla outlined how farms can reduce the prevalence of APR on farms:
”Farmers should not dose and move animals to clean pastures; animals should be returned to dirty pastures. This dilutes the number of resistant worms in the pasture, meaning they reproduce at a slower rate.
”Moving animals to fresh pasture after dosing will only allow for resistant worms to multiply quicker.
”The use of fecal egg counts should be used to identify animals that require dosing rather than following on a set time-line.”
Fecal egg counts are, generally, useful for performing routine parasite surveillance on a farm and designing a parasite-control programme based on the findings.
”Farmers should also, where possible, avoid treating older animals, where worm burdens will not have as big of an impact,” she added.
Farm case study
Niamh Field, a research officer with Teagasc, outlined an example of a case study of a farm that had reduced the use of anti-parasitic products.
Niamh explained: ”The farm had been blanket dosing all the calves and heifers at regular intervals for worms, with no evidence of high-worm burdens.
“The farmer then began monitoring worm egg counts, using grouped fecal egg counts to become more strategic with the farm’s worm dosing.
”The farmer began monitoring [the] weight of calves as a way to detect possible illness within the calves.
”The farmer also increased the amount of time spent herding the youngstock to detect issues at an earlier stage.”
Results
By adopting these simple steps and by the use of fecal egg counts, the farmer was able to determine that the heifers showed no sign of worm burden, while calves had a lower burden than the farmer had predicted.
This farm was able to reduce the cost of dosing replacement stock by half.
Niamh added: ”The cost of dosing is not high, but need for these products in the future should be enough to encourage farmers to reduce use of these drugs.”
Closing comments
Concluding, Orla said: ”The number of farmers using fecal egg counts is quite low, with a small increase seen when a scheme is introduced.
”My impression was that uptake of fecal egg count is static, with increased usage of this tool being required moving forward.
”Farmers should use fecal egg count to determine if dosing is required, what product is required and ensure that the correct amount is given.”
It is important to use the following steps when treating animals:
- The right product;
- The right animal at the right time;
- The right rate in the right way.