Effect of 131 I‐Induced Hypothyroidism on Indices of Reproductive Function in Adult Male Dogs

Abstract

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 131 I 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 131 I-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 131 I-induced hypothyroidism does not affect indices of reproductive function in adult male dogs.Key words: Luteinizing hormone; Scrotal width; Semen; Spermatogenesis; Testosterone.H ypothyroidism is a frequently diagnosed endocrine disorder in dogs. The most common causes of canine hypothyroidism are lymphocytic thyroiditis and idiopathic thyroid atrophy. 1 Hypothyroidism is reported to cause subfertility, poor semen quality, and decreased libido in several species, including people, rats, goats, and dogs, 1-7 but the mechanisms by which this occurs have not been elucidated. Lymphocytic thyroiditis associated with lymphocytic orchitis has been described as an inherited condition in a colony of Beagles. 2 Affected dogs had decreased testicular size and subfertility or sterility. Subnormal fertility and poor semen quality were reported in a colony of Borzois with lymphocytic thyroiditis, but testicular biopsies were not evaluated in those dogs. 8 In both colonies, hypothyroidism did not develop until dogs were Ն2 years old. Lymphocytic thyroiditis and lymphocytic orchitis are considered to be immune-mediated diseases. Whether hypothyroidism causes decreased fertility or whether decreased fertility is a result of lymphocytic orchitis that occurs simultaneously with, but not as a direct result of, lymphocytic thyroiditis is unknown. Whether hypothyroidism in the Beagle and Borzoi colonies is representative of canine hypothyroidism is also not known. The purpose of this study was to evaluate the effects of experimentally induced hypothyroidism on reproductive function in adult male dogs. Materials and Methods Dog Selection and Study DesignNine male Beagles, 11-17 months of age, weighing 10.9-15 kg, were determined to be normal on the basis of physical examination, negative Brucella canis serology, normal libido, normal seminal characteristics...

Concentrations of Prolactin, LH, Testosterone, TSH and Thyroxine in Normospermic Dogs of Different Breeds

“…Nevertheless, we conclude that primary or secondary hypothyroidism can be excluded in these dogs, as basal TSH concentrations were at physiological levels and TRH injection induced a clear TSH increase in all dogs of this breed. Normal semen quality, in contrast, is not a relevant parameter as regards thyroid assessment, as Johnson et al (1999) reported that no relation exists between hypothyroidism and disturbed fertility in male dogs.…”

Hypothyroidism

“…However, work by C. Johnson, et al (1999) in Beagles failed to document any deleterious effect of experimentally induced hypothyroidism on any aspect of male reproductive function. However, work by C. Johnson, et al (1999) in Beagles failed to document any deleterious effect of experimentally induced hypothyroidism on any aspect of male reproductive function.…”

Effect of repeated semen ejaculation on sperm quality and selected biochemical markers of canine semen

“…However, in dogs, extragonadal sperm reserves are rarely completely depleted in the course of 5-7 days. In the work of Johnson et al (1999), extragonadal sperm reserves in dogs became completely depleted after 10.5 days on average. In general, total sperm counts in ejaculates from healthy adult dogs should reach 200-300 million to 1 billion.…”