AbstractVolatile fatty acids (VFAs) were measured in slurry stored in farm and laboratory conditions. All slurries from farm sources contained VFAs; acetic acid was predominant, followed by propionic, n‐butyric, iso‐butyric, iso‐valeric and n‐valeric. On average, pig slurry contained more total VFAs than did cow slurry. VFAs persisted in anaerobic conditions but decomposed rapidly when air was passed through slurry in laboratory experiments; decomposition was slower when air was passed over the slurry surface. Very little VFA formed when anaerobic conditions were re‐imposed on aerated slurry unless glucose or protein hydrolysate was added. The pH of slurry was increased by passing air or nitrogen through it and decreased by addin