Hypothyroidism Spay/neuter in dogs was found to be correlated with a three fold increased risk of hypothyroidism compared to intact dogs. The researchers suggest a cause-and-effect relationship:
Castration increases the severity of autoimmune thyroiditis in mice” which may explain the link between spay/neuter and hypothyroidism in dogs. Hypothyroidism in dogs causes obesity, lethargy, hair loss, and reproductive abnormalities.