Canine Reproduction - Common Questions Part 2

These notes form part of the Dogs NSW Member Education Breed Seminars, held on DOGS NSW grounds - Dr. Ciaran Galvin MVB (UCD IRELAND)

 

COMMON QUESTIONS WHICH YOU MAY OR MAY NOT KNOW THE ANSWERS TO?

‘To castrate or not to castrate’, that is the question?
While studies have demonstrated the safety of castration in dogs as young as 7 weeks of age, there are no prospective long- term studies demonstrating the optimal age for castration of male dogs.
Pros of castration include a decrease in incidence of sexually dimorphic behaviours, and decreased incidence of diseases of the prostate and testes. The sexually dimorphic behaviours best controlled by castration are mounting, roaming, and urine marking. Aggression is often not controlled by castration, as the underlying cause of aggression is usually not hormonal. Testicular neoplasia is very common in dogs, with a reported incidence of 0.9%. Testicular tumours usually arise in aged dogs and are rarely malignant; castration is curative. Prostate disease is very common in intact male dogs. By 6 years of age, 75 to 80% of intact male dogs have histologic or clinical evidence of benign prostatic hypertrophy (BPH) . BPH is usually not associated with severe clinical signs but does predispose the dog to prostatitis. Castration is a cure for BPH and promotes resolution of prostatitis.
Cons of castration. Obesity is the most common nutritional disorder in dogs and multiple retrospective studies have demonstrated a correlation between castration and weight gain. Weight gain is easily controlled by the owner.

Are there alternatives to castrating my dog?
In males the Hormones FSH and LH are required for normal male fertility. The negative feedback effect of progestins is not enough to significantly impair spermatogenesis in male dogs. Similarly, administration of testosterone and androgen antagonists has not been demonstrated to impair spermatogenesis.

Superlorin®
Suprelorin® is a subcutaneous implant designed to prevent fertility and suppress libido in male dogs for a minimum of six or twelve months, depending on the size of the implant (4.7 vs. 9.4mg).
The implant, placed beneath the skin between the shoulders, releases a slow and continuous dose of deslorelin, a gonadotropin-releasing hormone (GnRH) analog. Deslorelin suppresses the reproductive endocrine system by preventing the production of pituitary hormones and testosterone, the male gonadal hormone.

So long as deslorelin is being released, the dog remains infertile and behaves as if castrated. (Note, however, that the manufacturer reports that it will generally take 2-3 weeks after implantation for testosterone to be reduced, and about 6 weeks to become infertile due to sperm stored in the reproductive tract).

Superlorin®  offers value for dogs who cannot safely undergo surgery, persons who wish to prevent fertility and testosterone production without castration (dogs can receive sequential implants), and persons who are unsure about castration and want to “trial” a “castrated” dog—for example, persons who want to ensure that castration would not impact their dog’s working, herding, or hunting abilities.

I heard hypothyroidism affects fertility. Is this true?
Hypothyroidism is the most common endocrine disorder in dogs. Most cases are due to autoimmune thyroiditis and the inciting cause is rarely identified.

Accurate diagnosis requires demonstration of decreased serum concentrations of free T4 and increased concentrations of thyroid stimulating hormone.

Hypothyroidism has been anecdotally associated with decreased libido, poor semen quality, and retrograde ejaculation in dogs. However, no study has demonstrated a cause- and- effect relationship between hypothyroidism and fertility in male dogs. Because hypothyroidism is caused by autoimmune destruction of the thyroid gland with subsequent atrophy, it is possible that concurrent autoimmune destruction of the thyroid and gonads may be responsible for this apparent link. Several studies in male dogs suggest this connection. This does not explain why some hypothyroid dogs with poor reproductive function return to normal fertility when properly supplemented with thyroid hormone.

Are there any Nutritional supplements to improve fertility?
Compounds commonly described as nutritional supplements that enhance semen quality in dogs are those containing glucosamine, most commonly in preparations for joint health, and those containing amino acids, specifically L- carnitine.

While carnitine is secreted in the canine epididymis, the site of maturation of spermatozoa we do not know if it has any role in improving motility of sperm.

Omega- 3 fatty acid supplementation has been demonstrated to improve motility of frozen- thawed spermatozoa in stallions and to improve motility and sperm concentration in the boar.
Treatment of subfertile men with an antioxidant preparation has been associated with increased linear velocity of spermatozoa and increased pregnancy rate. In rats, consumption of pomegranate juice, which contains vitamin C and several antioxidant compounds, was associated with improved semen quality. Vitamin, mineral, and herbal therapies marketed for enhancement of libido or semen quality have not been proven to be of benefit in dogs; however, no scientific studies have been reported.

This article appeared (with permission) in DOGS NSW magazine, February 2018 edition.