“If you love your animal very much, this is what you must do for them, for their good rebirth and quick liberation from samsara. When the animal is dying or has died, recite OM MANI PADME HUNG, Heruka mantra and Heruka root mantra, and other mantras such as the Milarepa and Namgyalma mantras. You can recite the long mantras 21 times or more, and one mala or more of the short mantras. Blow strongly on the animal’s body after each recitation. Or, you can blow on water, visualizing each deity absorbed into the water. Each drop of water now has the power to purify negative karmas. Then, as you pour the water on the animal, all its negative karmas are purified.
If the animal is dying, you can do Medicine Buddha practice, visualizing the seven Medicine Buddhas on the crown of the animal. Then, you can also do 35 Buddhas practice, with nectar coming out of the 35 Buddhas and purifying the animal’s negative karma. Do this with strong refuge in the 35 Buddhas to protect and guide your animal.
When the animal is in the process of dying or even after its breath has stopped, if you have some sand from a Kalachakra sand mandala, you can mix it with butter and put it on the crown of the animal’s head. Each sand grain has many Buddhas abiding in it. It’s especially good if it has been blessed by His Holiness the Dalai Lama”. [3c]
Lama Zopa Rinpoche