Equine internal parasite management plays a crucial role in maintaining horse health and welfare. In collaboration with the British Equine Veterinary Association, The British Horse Society has created their ‘Think Before You Worm’ campaign, which emphasises the importance of developing personalised de-worming plans for horses – it is based around regular testing and understanding of local management practices to combat the development of parasitic resistance. By following evidence-based recommendations and collaborating with horse owners and yard managers, vets can manage internal parasites successfully while preserving the effectiveness of anthelmintics.
The dangers of worm infestation
It should not be forgotten that internal parasites have the potential to compromise the health and well-being of horses, and may also have a significant impact on equestrian businesses. Yard owners and managers can potentially face great reputational damage if their property develops populations of multiresistant worms, including a loss of clients and income as well as pasture that can no longer be used to graze horses. Once resistance develops on a property it cannot be reversed. Yard owners should do all that they can to protect their pasture and business by:
- Co-ordinating de-worming programmes: Encourage a whole-herd approach and establish co-ordinated testing schedules for the entire yard, rather than leaving individual owners to test and treat horses independently.
- Effectively testing, treating and isolating new horses: where isolation is not possible, it is advised to encourage any new livery to perform faecal worm egg counts and tapeworm antibody tests prior to their horse's arrival on the yard.
- Minimise the use of anthelmintics once horses are on the property through implementation of tailored diagnostic led de-worming programmes.
Assessing parasite risk
Assessing a horse's parasite risk should inform decision making when developing deworming programmes. Assessing risk includes checking multiple factors that can influence a horse's chances of acquiring a worm burden. These risks can be broken down into clinical history, age, number of horses on the pasture, faecal worm egg counts and tapeworm antibody test results and the environment. Assessing these risk factors enables horse owners and yard managers to categorise their horses into low-, medium- or high-risk groups based on their potential for parasite infection. It is important to note that even if a horse falls under the low-risk category, it does not imply an absence of risk altogether.
Vets can assist horse owners and yard managers with assessing the parasite risk to develop a comprehensive and effective ongoing parasite control plan, ensuring the wellbeing of all horses under their care. This proactive approach to parasite management aims to minimise the impact of parasitic infections and promote the overall health and welfare of horses.
The importance of regular testing
Regular testing is vital to assess levels of parasite shedding onto pasture (tested with faecal worm egg counts) and exposure to tapeworms (using ELISA tests) and guide appropriate treatment strategies. Decades of regular blanket de-worming without prior testing has led to the emergence of resistance to all of the anthelmintics that are currently available.
With the increase in resistance to anthelmintics and the damage they can cause to the environment, it is important to make sure every treatment is justified and drugs are not being used when they are not needed.
Testing frequency
The timing and frequency of testing should be determined when developing a herd health plan, depending on the horse's and herd's risk of worm infection. Where the risk is deemed to be higher, tests should be performed more frequently. Testing should ideally be carried out on all horses in the group at the same time.
The more faecal worm egg counts that can be performed the better, as more information can be gathered on the risk of parasitic infection within any group of horses. However, in most populations, performing faecal worm egg counts every 8–12 weeks through March to September is appropriate. Over winter, there is less egg shedding and horses generally spend more time stabled, so there is less value in performing faecal worm egg counts during this time and less need to treat (Rendle et al, 2019). Tapeworm antibody testing on serum or saliva should be performed every 6–12 months (determined by level of risk), at least initially, to inform on the need for treatment.
Economic concerns have been acknowledged as a barrier for horse owner compliance in relation to testing, however, the use of faecal worm egg counts in a targeted worming strategy has been shown to reduce the cost of deworming when compared with intensive interval treatment protocols (Lester et al, 2013).
Taking steps to slow resistance
With the support of vets, horse owners and yard managers should be assessing whether resistance is present to different anthelmintics on an annual basis by using simple faecal worm egg count reduction tests. Knowing the pattern of resistance on a property allows for appropriate planning of future treatments to ensure horses only receive treatments that are effective.
As vets, encouraging clients to follow these three simple steps will be crucial in slowing and preventing the development of resistance:
- Co-ordinate de-worming programmes across equine properties based on individual horse and herd requirements and informed by the results of diagnostic testing. This approach minimises the risk of resistance developing and promotes optimal parasite control.
- Annual faecal worm egg count reduction tests, testing a different class of anthelmintic each year on rotation.
- Ensuring a holistic approach that combines good pasture management, appropriate stocking and faecal worm egg counts. By implementing these strategies and taking a proactive and integrated approach to parasite management, horse owners, carers and yard managers can maintain the health and well-being of horses in their care while minimising the development of drug-resistant parasites and reducing reliance on anthelmintics.
Conclusions
The Think Before You Worm campaign, with its focus on evidence-based recommendations, collaboration and tailored approaches to equine parasite management, is a significant step towards preserving the health and welfare of horses while safeguarding the longterm efficacy of anthelmintic treatments. By following these principles and encouraging horse owners and yard managers to adopt responsible parasite control practices, vets can have a substantial impact in combating worm resistance and ensure the well-being of all horses.