One hundred fifty-five of 201 cattle from 3 different farms showed clinical signs and died of botulism after eating the same batch of poultry litter contaminated with poultry and rodent carcasses. The cattle had access to poultry litter for only 1 d; afterwards it was removed from the diet. Death occurred over a period of 17 d after the poultry litter intake. The peak mortality was on day 4; 20 animals died within 10 d of the ingestion. The greater the intake of poultry litter, the higher the cattle mortality. Three steers which died on the first day had peracute effects while the remaining cattle showed classical signs. Twenty-five of the 46 surviving cattle had mild clinical signs, but recovered in a few days. Type C Clostridium botulinum toxin was found in extracts of the poultry litter, carcasses and cattle intestinal contents. Nutrient composition of the poultry litter was normal but pH was lower (6.9) than usual (7.5 to 9.3).