RAO (Recurrent Airway Obstruction) is a common chronic respiratory disease of horses. The present study aimed to investigate, whether oral supplementation of long chain omega-3 fatty acids (LC omega-3 FA), derived from seal oil, modulates the plasma and leucocyte-phospholipid fatty acid composition in equines, has an impact on inflammatory processes induced by RAO and therefore has a favourable effect on the lung function of these horses. Using a cross-over study design, a feeding trial with nine adult horses affected by RAO was performed. Each animal received a diet which was supplemented by seal oil (STO) at a dose of 160 or 320 mg/kg bodyweight (BW) per day or the same amount of sunflower oil (SBO) for ten weeks each. Fatty acid compositions of plasma and leucocyte-phospholipids were analysed by GC.
Lung function measurements, bronchoalveolar lavage fluid (BALF) cytology and clinical examinations were performed. Data were analysed using Mann-Whitney-, ANOVA- and Scheffé-tests. Supplemented oils were well accepted and tolerated. Different diets clearly affected fatty acid composition of plasma and leucocyte-phospholipids. A significant decrease (p;0,05) in the C18:2 omega-6 percentage could be observed in plasma and leucocyte-phospholipids after STO diets, as well as an increase in C20:5 omega-3 and C22:6 omega-3. C22:5 only increased in plasma. Total BALF leucocytes were reduced significantly by STO supplementation (p;0,05), neutrophil granulocytes were reduced tendentially (p=0.1). Breathing frequency increased during the trial, but no differences between the STO- and SBO-group was seen. Neither lung function nor the other clinical signs could be influenced by STO or SBO diets. Supplemented LC omega-3 FA were effectively incorporated by horses, showing a time-dependent tendency for accumulation. The omega-6:omega-3 ratio was reduced by STO, which could possibly have antiinflammatory effects. The reduction of BALF cell counts might be the result of such effects. To investigate the possible mechanisms of action of LC omega-3 FA in horses with RAO, a long-term study should be conducted, that also addresses the involvement of antiinflammatory mediators.