Lama Zopa Rinpoche with a student’s pet dog in Italy recently. The advice below was provided to another student requesting Rinpoche for advice on how to purify his dog’s negative karma.

Regarding purification for yourself and your dog, take strong refuge in the Buddha and think that the Buddha sends light to yourself and your dog, and to any other animals or beings you want to think about. Think nectar comes from the Buddha and purifies the negative karma, created from beginningless time, of yourself and the dog and other beings you are thinking about.

Then recite the refuge prayer. Keep reciting the refuge prayer while visualizing the Buddha sending nectar out of his compassion and loving kindness, like sunlight, to yourself and your dog. It’s like switching the light on in a dark room; it totally purifies the negative karma created since beginningless rebirths. You can keep the dog nearby when you do this so the dog can hear you reciting the refuge prayer. This leaves an imprint on the dog’s mind and plants the seed of enlightenment.

If there is no stupa near where you live, then maybe you can go to a center that has a stupa. If you are able to go there that would be very good, then you take your dog around the holy objects, the stupas. Go around the holy objects as many times as possible with the dog. This purifies the negative karma collected since beginningless rebirths, therefore go around as many holy objects as possible with the dog.

This advice, “How to Purify a Dog’s Karma,” is from “Lama Zopa Rinpoche’s Online Advice Book,” published in September 2018 on the Lama Yeshe Wisdom Archive website:
https://www.lamayeshe.com/advice/how-purify-dog%E2%80%99s-karma