The Effect of Insect Bite Hypersensitivity on Movement Activity and Behaviour of the Horse

SIMPLE SUMMARY: Insect bite hypersensitivity (IBH, “sweet itch”) associated with Culicoides biting midges is the most common allergic skin disease in horses, seriously reducing the welfare of affected horses. This study (1) investigated the effect of IBH on animal welfare and behaviour and (2) assessed a new prophylactic repellent. There were no differences in movement activity and observed behaviour between IBH-affected horses and control horses. However, horses displayed more itching behaviours (e.g., body shaking and scratching) in the evening than in the morning and should therefore be stabled/protected by, e.g., insect repellents and a protective horse blanket in the evening, when Culicoides are most active. Even short periods of scratching were associated with moderate/severe inflammatory skin lesions. In order to improve welfare in IBH-affected horses, even short-term exposure to Culicoides should be avoided. Preliminary results indicated that the new repellent can be used as a safe, non-toxic, environment-friendly prophylactic to potentially reduce allergen exposure and prevent signs of IBH, although further studies are needed to determine its efficacy. ABSTRACT: Insect bite hypersensitivity (IBH) associated with Culicoides biting midges is a common allergic skin disease in horses, reducing the welfare of affected horses. This study investigated the effect of IBH on animal welfare and behaviour and assessed a new prophylactic insect repellent. In total, 30 horses were recruited for a prospective cross-over and case–control study. Clinical signs of IBH, inflammatory markers in skin biopsies and behavioural data (direct observations, motion index) were scored longitudinally during two consecutive summers. No differences were observed in the total number of itching behaviours or motion index between IBH-affected horses and controls, but higher numbers of itching behaviours were observed in the evening. IBH-affected horses showed both clinical and histopathological signs of inflammatory skin lesions, with even short periods of scratching being associated with moderate/severe inflammatory skin lesions. In order to improve the welfare of the IBH-affected horses, they should be stabled/given extra protection in the evening and even short-term exposure to Culicoides should be avoided. Preliminary results showed that the repellent tested can be used as a safe and non-toxic prophylactic to potentially reduce allergen exposure in horses with IBH, but further studies are needed to determine its efficacy.