Neither should dolphins drink cat's milk, nor squirrels drink camel milk. That is not nature's plan. Instinctively, we know that dog's milk and pig's milk contain substances best suited for those specific species. Most human adults would be disgusted at the thought of consuming canine or porcine hormones, lactoferrins or immunoglobulins. All hormones regulate one or more of the thousands of metabolic processes occurring every second inside of the human body.
Some hormones regulate cellular metabolism.
Vitamin D, the sunshine vitamin, is actually a steroid hormone. In the 1850's, scientists first recognized that the thyroid gland produced a substance which regulated metabolism. A decade later, it was noted that the pancreas acted as a gland, secreting a substance that would later be identified as insulin. Hormones are chemical messengers. Adrenalin is a hormone.