Tea tree oil is often found in varying concentrations and should never be used on pets. As little as 7 drops of 100% oil has resulted in severe poisoning, and applications of 10-20 mls of 100% oil have resulted in poisoning and death in both dogs and cats. Clinical signs include a low body temperature, weakness, walking drunk, inability to walk, tremors, coma, increased liver enzymes, and even death.
http://www.petpoisonhelpline.com/poison/tea-tree-oil/
http://www.petpoisonhelpline.com/poison/tea-tree-oil/