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How to keep your dog or cat at its correct weight
Know the issues related to obesity.
The first step in combating pet obesity is to make sure your pet is not suffering from a medical illness that either contributes to obesity or is a complication from being overweight. In dogs and rarely in cats, hypothyroidism, or low thyroid hormone levels, can cause a pet to gain weight.
Hypothyroidism can also cause a dog's hair to thin or fall out in patches. The dog may also become less playful and energetic.