Bovine botulism of Clostridium botulinum type D occurred in 11 farms from January 2009 to March 2014 in Okayama Prefecture, Japan. In the 11 farms where botulism neurotoxin type D was detected in bovine feces, among the environmental samples (cattle feed, water, farm swabs, wild animal feces), the detection rate was highest in wild animal feces (from four of eight farms). C. botulium type D was isolated from two cases, and these isolates were a mosaic of type D and C neurotoxins (D/C mosaic neurotoxin). These isolates showed the same band pattern as a result of pulsed-field gel electrophoresis analysis. Nine of the farms were located within a 20-km radius, and the two farms where the strain was isolated did not have any epidemiological relationship. At the farm where the vaccine was used, a cow to which the vaccine had not yet been administered developed bovine botulism, and in this case, high levels of botulinum neurotoxin were detected in the environmental samples in the cowshed. These results suggest that wild animals were involved in the spread of C. botulium. The vaccination of cattle is effective in suppressing the occurrence of bovine botulism, but it is unable to inhibit C. botulium discharge in feces. For prevention of the spread of C. botulium between farms, the most important measures are to thoroughly clean and disinfect the cowsheds and to prevent the intrusion of wild animals into the farm.