Copper is an essential mineral for dogs, cats, humans — and all living things, for that matter.
So, you’ll almost always find some form of copper on a dog food label. That’s because in order to legally claim the product is “complete and balanced” for nutritional adequacy, a dog food must contain sufficient copper to meet AAFCO nutrient profiles.
According to the official 2015 AAFCO publication, a dog food must contain at least 7.5 mg of copper per each kilogram of dog food (on a dry matter basis, of course).
However, any mineral (even sodium) can be toxic in excessive amounts. The maximum for copper as published by AAFCO is currently 250 mg.
Because some compounds of copper have such poor bioavailability for dogs, AAFCO does not permit its oxide form (like copper oxide, cupric oxide, etc.) to be used to meet the association’s official nutrient profiles.
So, manufacturers must use copper sulfate or a chelated form of the mineral such as copper proteinate (or copper complexed with an amino acid or polysaccharide).
The personal interest (lay) article mentioned by Susan Thixton that was published in The Battle Creek (Michigan) Enquirer appears to base its warnings on a hypothesis proposed by one well-meaning veterinarian.
And his “theory” is certainly worthy of further investigation.
However, until a scientific study that addresses the specific topic of copper sulfate toxicity in dogs can be referenced, I would suggest to those concerned to avoid the hysteria about these recent claims.
Please read this pet food industry article about copper sulfate written by a respected animal nutritionist, Dr. Greg Aldrich of Kansas State University for a more enlightening and scientific explanation.
Hope this helps.
