Thyroid issues in reproduction.

Observations in people and animals demonstrate relationships between thyroid and reproductive functions. Thyroid issues of importance to small animal reproduction are twofold. First, some thyroid disorders, such as lymphocytic thyroiditis and some forms of congenital hypothyroidism, appear to be heritable. Those traits might be considered undesirable. If so, to eliminate the trait affected animals would not be selected as breeding stock. Second, thyroid disorders may adversely affect fertility, pregnancy, or neonatal health. If a causal relationship existed between thyroid and reproductive disorders, correction of one would be expected to result in resolution of the other. This is often not the case. Although animals and people with thyroid disorders may also have reproductive disorders, usually disorders other than thyroid disease are the cause of reproductive abnormalities. It appears that euthyroidism supports optimal reproductive performance, but clinically significant reproductive dysfunction is manifested only under certain uncommon conditions of thyroid disease in dogs and cats.