Effect of 131I-induced hypothyroidism on indices of reproductive function in adult male dogs

Hypothyroidism has been cited as a cause of infertility, abnormal semen quality, and poor libido in people and animals. The purpose of this study was to evaluate the effect of hypothyroidism on variables indicative of reproductive function in adult male dogs. Nine normal dogs were randomly assigned to 2 groups. Hypothyroidism was induced with 131I in 6 dogs. Three dogs remained untreated, normal, and euthyroid. Thyroid hormone concentrations, body weight, clinical signs, and reproductive function were determined for each dog every 3 months for 2 years. Reproductive function was assessed by determining daily sperm output, total scrotal width, spermatozoal motility and morphology, libido, and serum testosterone and luteinizing hormone concentration responses to exogenous gonadotropin-releasing hormone. The 131I-treated dogs developed clinical and laboratory signs of hypothyroidism. In the hypothyroid dogs, serum concentrations of thyroid hormones were consistently below the reference range and were significantly lower than that in the euthyroid dogs. There was no difference in reproductive function between the hypothyroid and euthyroid dogs. The results of this study show that 131I-induced hypothyroidism does not affect indices of reproductive function in adult male dogs.