I have nothing to add about attuning pets, but I did want to mention that I have two loving dogs in my life, Snickers and Cody.
Cody is a gentle and old soul. He loves getting reiki treatments. Our reiki treatments have appeared to lower his anxiety about fireworks and thunderstorms.
Snickers on the other hand wants nothing to do with reiki. I've even thought that perhaps hands on was too much for him, so I tried to give him distance reiki, but when I asked if he'd like to receive it, it was a resounding "NO!".
Makes me chuckle. I often say they are yin/yang. One mellow, one tense. One black, one white. They are very delightful indeed.