Milk and milk proteins have been around for eons. While likely not a large part of dog or cat diets beyond the weaning period, some milk constituents have periodically found their way into pet diets for years -- likely as leftovers from the family's cereal bowls.
Most texts instruct us to avoid feeding milk products to cats and dogs past weaning as they lose the lactase enzyme activity necessary to utilize the lactose sugar found in milk. However, it is becoming increasingly common to find petfoods that contain whey, a milk protein, as a prominent ingredient on their labels.
