Presentation Description / Session Abstract: Alternative treatment options to glucocorticoids for equine asthma is desirable due to withdrawal time and risk of laminitis. The objective of this study was to evaluate if RGT (Respiratory Gene Technology), a commercial kit to produce autologous conditioned serum, was effective in reducing bronchoalveolar lavage (BAL) neutrophils and mast cells in racehorses with cytological evidence of mild equine asthma (MEA). Racehorses in active training were enrolled in the study; a control group (n=11) with normal BAL values, a RGT (n=12) and a serum treatment group (n=13). Endoscopy including BAL was performed before the treatment (T0), after a six-week treatment period including 12 intramuscular injection of RGT or serum (T6) and as a follow-up 10 weeks after last treatment (T16). Regarding the control group, no difference between any of the time point was found. A significant decrease in BAL neutrophils (RGT p<0.01; serum p<0.01) and mast cells (RGT p=0.02; serum p<0.01) was found for both the treatment and placebo group between T0 and T6. A significant difference between T0 and T16 was found for BAL neutrophils in the serum treatment group (p=0.05) and BAL mast cell groups (RGT p<0.01; serum p=0.03). No difference was found between T0 and T16 for BAL neutrophils for the RGT group (p=0.49). Preliminary results from this study showed that intramuscular treatment with both RGT and serum was effective in reducing BAL neutrophils and mast cells in horses with MEA. Further studies are necessary to evaluate the long-term effects as well as comparison to other treatment options.