From Petfood Industry:

Excessive quantities of minerals in dogs’ diets have become more of an issue over the years, as high meat diets and nutrient supplements have become more common. Copper is one nutrient that can be a double-edged sword.

Recently, Greg Aldrich, PhD, discussed the health effects of copper in dog food. Although all dogs need copper in their diets, a small percentage of dogs suffer from a problem with copper storage in their bodies. Copper can build up in their liver and cause hepatitis, cirrhosis and other diseases.

For those dogs that might be prone to copper storage disease, a lower copper and higher zinc diet may prove beneficial. There remains little doubt that diet could exacerbate the condition in affected dogs. For the rest of the dog population, scientists don’t know if the copper issue is a diet-induced condition, but Aldrich considered it unlikely.

In 2012, Petfood Industry reported how meat-first diets may result in overages for a number of nutrients, especially protein, fat, calcium and phosphorus. In general, the higher the level of meat in a pet food, the higher the concentration of calcium, phosphorus, magnesium and certain micro-minerals.

In a dog’s body, copper can act as a pro-oxidant at high concentrations. This can result in the production free radicals, which are particles that can damage cell membranes, nucleic acids and cellular protein. Free radicals may also reduce shelf life of extruded pet foods.

Avoiding mineral excesses for optimal pet nutrition

'The implication to consumers is that meat-first diets are better for their pets.', 'Elevated trace mineral concentrations are also common in petfoods relative to AAFCO recommendations.'] Many petfood companies stress the importance of meat-first formulations. The implication to consumers is that these diets are better for their pets.