We exist in a universe of energy and our human bodies are made up of energy; animals are no different. Just like us, when your pet's energy is balanced, they are more relaxed and more likely to be healthy. When it is 'low' or unbalanced, they'll often be more easily affected by stress and less resistant to illness. Reiki is the universal life force energy that flows around and through all living beings. Therefore, this wonderful holistic practice can benefit animals in the same ways as humans.
Animals cannot give us verbal permission, so we don't really 'do' Reiki on animals, we offer it to them and since the practice is about connecting hearts, not hands, treatment can be directly on the body or some pets may prefer to experience the energy from a distance rather than hands-on. Reiki energy does not come from the practitioner but through them. Animals respond to your loving touch as well as intention, so whether the animal is open to it and happily allows physical contact, or stays on the other side of the room, treatments are equally effective.
Depending on the location, some of the treatment rooms I work from allow pets, so if you're booking in for a Reiki session for yourself, why not bring your pet along to experience the energy in the room; some regular clients do this, and their pets love it!