What about added vitamins. It's utter nonsense to assume that the pet food manufacturers make pet food for the sake of keeping your dog healthy. It is possible to produce a pet food based on shoe leather, used motor oil, coal and water, which if analyzed would meet the legal requirements necessary for it to be sold as pet food. By law, pet foods are not required to contain optimum or best levels of each nutrient. Consequently we see excesses of protein, calcium, phosphorus, magnesium, and sodium to be common in pet foods.
Lets take excess calcium as an example because it is probably one of the most common problems.
The calcium combines with zinc, producing a compound which cannot be absorbed, resulting in a zinc deficiency. Lets take a quick look at how mother nature designed the dog to eliminate the problem of calcium combining with zinc. Normally the liver will be eaten along with maybe the gut contents and perhaps some of the muscle meat. The calcium is eaten at another meal when he eats the bones. Seldom, if ever will both be consumed at the same time.