Kidney function in the newborn is 25 percent of what it will be later in life. These immature kidneys are unable to concentrate urine, and puppies therefore excrete large amounts of dilute urine regardless of whether they take in fluids. Thus, dehydration is a complicating factor whenever puppies become too weak to nurse. This is another reason why it is important to begin supplemental feedings as soon as a puppy stops nursing or stops gaining weight.
Signs of dehydration are lack of moisture in the mouth, a bright pink color to the tongue and mucous membranes, and loss of muscle tone and weakness. When the skin is pinched, it stays up in a fold.
Neonatal diarrhea is a serious cause of rapid dehydration and weight loss. When diarrhea occurs during hand feeding, it usually clears up when the strength of the formula is changed. In all other cases of diarrhea, the puppies should be seen and treated by a veterinarian.