Observations on the epidemiology and control of Strongylus vulgaris infections.

This research article presents results from a series of experiments conducted at the University of Utrecht from 1981 to 1984 which studied the epidemiology and control of Strongylus vulgaris infections in horses. Findings suggest that administering anthelmintics and moving horses to clean pastures in July can effectively control these infections, as can treating horses with anthelmintics in April and throughout the summer. The study also finds that S. vulgaris larvae can survive on pastures until autumn, outlasting other gastrointestinal nematodes, and may transfer from free-living stages to infective between May and July.

Study Design and Findings

• The researchers conducted four small grazing experiments with horses between 1981 and 1984. The focus of their study was on the patterns and control of Strongylus vulgaris–a helminth that infects the horse’s blood vessels, particularly the cranial mesenteric artery.
• Groups of horses who were treated with an anthelmintic (a type of anti-parasitic drug) in July and subsequently moved to a clean pasture showed negligible S. vulgaris burdens by the end of the year. This indicates that a combination of medication and pasture rotation can be effective strategies for controlling S. vulgaris infections.
• In contrast, horses that were treated with the same anthelmintic in July but remained on the same pasture were found to have considerable arterial S. vulgaris deficits. Similarly, a group of horses set to graze on a previously used pasture and treated with another anthelmintic (albendazole) in the spring and summer also showed significant S. vulgaris infections.
• Notably, a tracer horse that grazed with the latter group from mid-September to mid-November had an even higher burden of arterial S. vulgaris larvae. This finding stresses the role of pasture contamination in the transmission of S. vulgaris.

Insights about S. vulgaris Survival on Pastures

• The study also yielded valuable insights about the survival of S. vulgaris larvae in pastures. The researchers found that these larvae do not only survive winter, but also remain in considerably high numbers until autumn–a standing that is longer than that of most other types of gastrointestinal nematodes affecting horses.
• There were also signs suggesting that the translation–or transformation–of infective S. vulgaris larvae, which survived the winter in free-living stages on pastures, occurred between May and July.

Implications of the Study

• This extensive research underscores various effective approaches to controlling S. vulgaris infections in horses. Key among these is the use of anthelmintics in combination with rotational grazing practices. The findings recommend the relocation of horses to clean pastures following treatment, rather than leaving them on the same contaminated pastures.
• The ability of S. vulgaris larvae to survive on pastures for long periods–and their potential to transform into infectious agents from May to July–highlights a crucial aspect that must be considered for successful S. vulgaris control strategies.