If it meets the criteria of a business. The tax payer must have things like a business plan, a clear profit motive, solid income and expense records, etc. if he animal is a previous family pet turned K9 superstar and the business criteria are met then things directly related to the business aspect would be deductible. But things you would do for your family pet, like feed him, take him to the vet, basic grooming, etc would not be deductible.