Striking the right balance between monitoring and targeted treatments is essential to ensuring the responsible and sustainable control of roundworms, and other parasites, in cattle and sheep.
The economic burden of internal parasites in UK livestock is estimated to be £270m annually1. This includes not just the direct costs, such as treatments administered, but also indirect costs such as lost productivity.
This article will cover the general principles of responsible and sustainable roundworm control however it must be understood that there is no ‘one shoe fits all’ approach and you should work closely with your animal health advisor, to develop a health plan, which fits your stock and management system. This is important because the types of parasite, and associated risk, will vary between premises but also because the management of certain parasites (such as Nematodirus affecting lambs in spring) requires a different approach2.
Immune resilience
The long-term strategy, for most roundworms, should be to support the development of immune resilience. Healthy, adult animals with an immune system which is functioning well, should be able to regulate roundworms, maintaining a manageable burden, which does not impact health, welfare or productivity.
As previously discussed, there are exceptions such as Nematodirus in lambs which strikes before immunity has been able to develop or lungworm in cattle where, in spite of immune resilience developing well, it can be relatively short-lived meaning protection is not always maintained between grazing seasons.
In order for immune resilience to develop, we must allow livestock to be exposed to parasites however conversely, we must also ensure they are not overwhelmed which will impact their welfare and production efficiency. The rate at which they develop immune resilience varies depending factors such as the degree of exposure, the species of parasite and the underlying health of the host.
The benefits of allowing immune resilience to develop are that we can reduce our reliance on anthelmintics, deploying them only when necessary and in a targeted manner. This will save money and time dosing and by only using anthelmintics strategically, we will reduce the rate of development of resistance.
Resistance
Resistance is when a parasite has developed the ability to survive a dose of anthelmintic which would normally be effective. Certain factors such as underdosing or excessive use of anthelmintics will increase the rate at which resistance occurs.
This is problematic because resistant worms have the ability to transmit that resistance to their offspring. In order to prevent the resistant worms gaining a significant advantage, we aim to ‘preserve refugia’ and ensure that a susceptible proportion of worms remain within the host population.
The image on the right demonstrates what happens if we only treat a proportion of the animals, to retain susceptible parasites. Your animal health advisor can support you with rolling out such strategies.
Strategic use of treatments
While we have discussed reducing our reliance on anthelmintic treatment, we also need to understand that treatments will still be required, and we should aim to use them in a strategic manner.
Excluding parasites which require a different management approach (such as Nematodirus), we should generally aim to determine if the parasite burden is significant enough to justify treatment. Your animal health advisor can recommend the best method and timing- most frequently we utilise faecal egg counts as a cost-effective and rapid means of testing. Faecal egg counts can be carried out on individual animals or pooled to facilitate a ‘group mean’.
The results of a faecal egg count test provide an indication of gastrointestinal roundworm burden and your animal health advisor can determine if treatment is appropriate at that point in time.
It’s worth noting that a faecal egg count may not always be the most suitable test. Lungworm for example hatch in the intestines, meaning that larvae are shed, so an egg count would not reliably detect them. Another good example is liver fluke- eggs are only shed during certain periods when adult fluke are present.
Getting treatments right
Once the need to treat has been established, ensuring we get it right is critical. Your animal health advisor can discuss which type of treatment will be most suitable.
Once determined, review the method of application and check that you have the correct applicator and handling facilities to achieve this.
Applicators should be clean, in good working order and should be calibrated both before use and at regular intervals during use.
Make sure you dose for the heaviest in the group and group animals together into cohorts of similar weight to ensure the correct volume of anthelmintic is administered. Weight, especially on fully fleeced, pregnant sheep, can be surprising. Where possible use weigh scales to determine weight as accurately as possible.
Checking the effectiveness of the treatments used is also important. This is because factors like resistance or accidental under-dosing may have resulted in ineffective treatment. Samples are collected 7-14 days after treatment (depending on the group of anthelmintic used) to review this.
Prevention
In addition to the factors covered already, it’s vital to have a farm health plan in place to ensure you are taking the correct preventative measures at the correct time of year. This plan will cover control measures, such as biosecurity, to ensure the risk of buying resistant worms in is reduced.
To read more about responsible parasite control, visit the SCOPS website for sheep (https://www.scops.org.uk/) and the COWS website for cattle (https://www.cattleparasites.org.uk/).
What are my next steps?
There is no ‘one shoe fits all’ approach so it is important to work with animal health advisors to develop a sustainable approach.
Registered Animal Medicines Advisors (RAMAs) undergo intensive training and assessments, in addition to ongoing continuous education, to ensure that they are best placed to advise you on many aspects of animal health.
Your local Territory Manager would be delighted to discuss your approach to parasite control and advise on next steps for responsible parasite control.
This information was provided by Bimeda, marketers of the Micron kit for rapid parasite testing.
Date prepared: March 2024. Sustainable parasite control is integral to flock and herd health and productivity. Please consult your animal health advisor to determine which is the most appropriate approach for your management system.
1 Initial assessment of the economic burden of major parasitic helminth infections to the ruminant livestock industry in Europe. J. Charlier et al. Preventative Veterinary Medicine, Volume 182, September 2020, 105103. DOI: https//doi.org/10.1016/j.prevetmed.2020.105103
2 Nematodirus treatment during the mass hatching period in spring should not be based on diagnostics such as faecal egg counts but instead on the SCOPS forecast which can be accessed here: https://www.scops.org.uk/forecasts/nematodirus-forecast/