Control of gastrointestinal nematode species in horses: an evidence-based approach
Abstract
Evidence-based medicine implies that current literature is being utilised in order that the best therapeutic approach is used. This is especially important with regards to parasite control where the owner is relying on veterinary practices to provide them with the most current and cost-effective advice. With the current level of resistance to the most common nematode anthelmintics available it is clear that veterinary practices need to be doing more with regards to their own education on parasite control in order to be able to best inform owners. The nematode species that are of most clinical significance to the horse owner are the large redworms (particularly Strongylus vulgaris) small redworms (Cyathostomes), ascarids (particularly Parascaris equorum) and the pinworm (Oxyuris equi). They have a direct life cycle (no intermediate host) and the females are capable of producing thousands of eggs that can pass out in the faeces and then subsequently contaminate pasture and cause infection in susceptible horses. There are many factors that contribute to the clinical relevance of these species and much research has been undertaken into the factors that cause disease in susceptible equine populations. Many control strategies (for example faecal egg counts) and anthelmintic treatment programmes have been recommended in order to limit the clinical effects of these intestinal parasites; however due to the lack of clinical signs seen in horses most owners have relied on the routine prophylactic use of anthelmintics, and as a result anthelmintic resistance has become a growing concern. A better understanding by veterinary staff of the current research in this area would give them the ability to provide strategic therapeutic advice so that owners have a cost-effective and efficacious means of parasite control.
In a busy veterinary practice time is a precious commodity and the nature of equine practice has evolved significantly over the past few decades. Owners rely on veterinary staff to provide them with the most current and cost-effective advice regarding parasite control in their horses and while the term evidence based veterinary medicine (EBVM) is recognised, difficulties arise with regards to the types and levels of evidence and how to evaluate the rigour of different sources (Kaplan and Nielsen, 2010). In addition the wealth of horse-related magazines that offer advice on worming leads to the dissemination of information that is at times outdated and with a lack of peer review (Hinney, 2011). When trying to evaluate the numerous studies that are available with regards to anthelmintic resistance the problem arises in that there is a lack of universal agreement as to a definitive definition of what is anthelmintic resistance (Brady and Nichols, 2009). The literature suggests that owners are not getting the best advice, and the levels of resistance to the available anthelmintics provides evidence that veterinary practices need to be doing more with regards to both their own education and that of horse owners. One of the major obstacles with regards to provision of advice is that horses are kept under a variety of conditions and in particular there could be more than one veterinary practice providing advice on parasite control and, as such, advice can be based on an individual horse rather than the population of horses within an area. Livery yards present probably the greatest risk with regards to this due to high stocking densities, mixed and changing populations of horses and an environment where individual horse owners have less influence over parasite control programmes due to livery yard policy, and it has been suggested that the current interface between veterinary practices and livery yards is insufficient (Allison et al, 2011).
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