These 2 spellings are usually used interchangeably (in Australia and other English-speaking countries). However, in some specialist publications (notably the national, state and territory departments of agriculture), a distinction in meaning is made between the spellings:

• carcase: the body of an animal that has been slaughtered for meat (eg at an abattoir)
• carcass: the body of an animal that has died from natural causes, including disease or injury.