Puppies need mother's milk because it contains important ingredients like colostrum and DHA.When a puppy's mother does not produce milk or mother's milk is not available, a milk replacement can be used, but not Ensure.
Ensure is a meal supplement that is dense in calories, high in sodium and sugar. It is meant as a supplement for food in cases where the patient is to frail to eat or refuses to eat enough food. Puppy milk replacement is more than just calories and contains important vitamins and other nutrients specific for puppies.
Mother's milk is important to help puppies develop and gain weight. Without it, a puppy's immune system will not develop correctly and it can be more susceptible to illness. It will not gain weight properly and its chance for overall survival is diminished.
Milk replacement products for puppies contain all the nutrients a puppy needs and does its best to mimic mother's milk. Ensure does not have these nutrients including those for immune system development and instead only causes the puppy to gain weight.