Although I sometimes give my dogs their supplements in a bit of peanut butter, I wouldn't give it as a regular treat. Aflatoxins can be present in peanut butter. Aflatoxins are a group of naturally occuring fungi that produce toxic mold. They can be found in grains and commercial products such as peanut butter, cooking oils, cosmetics and so on. If you do give peanut butter once in a while, definitely use the natural product that doesn't contain any sugar or preservatives.