As a result, cells don't convert the nutritional energy it needs into biologically usable fuel as fast as usual. This decreased cell function causes a number of physical changes in a hypothyroid dog. Over a third become lethargic and mentally dull, and just under a third show hair or skin abnormalities. Hair-producing cells slow down, so there is less hair growth and more hair loss. Also, hypothyroid pets may suffer an increased propensity to joint disease, especially ligament damage.
Some veterinarians also suspect a link between behavior problems and hypothyroidism.
Increased aggression is the most commonly suspected behavior change, but some veterinarians speculate that a few hypothyroid dogs may develop anxiety- related or compulsive behaviors. If your pet develops a sudden behavioral change, have your dogs thyroid status examined. Since the physical signs of hypothyroidism develop gradually and vary from dog to dog, the disorder often goes undiagnosed. But veterinarians have found that hypothyroidism typically develops after 2 years of age and is more common in certain breeds such as golden retrievers and Doberman pinschers. While all owners should be on the lookout for changes in their dog's appearance or behavior that suggest hypothyroidism, owners of middle-aged dogs or genetically predisposed dogs should be especially watchful.