Maître de Conférences, Reproduction Animale - Ecole Nationale Vétérinaire d'Alfort (Paris)
Alfort Cedex, France
Advances regarding different aspects of canine male reproduction have been made in the past 5 to 10 years. This lecture will try to review the most practical ones, in various fields of veterinary andrology.
1. Recent Advances in Control of Reproduction
1.1. Surgical Control of Reproduction
Early spaying has been studied in male dogs, and also its effect on future health. However, in Europe, veterinarians are often reluctant to perform such early surgeries, although they bear no detrimental effect. The normal and side-effects of vasectomy in the dog have also been recently documented (Ferreira de Souza 2006, Perez-Marin et al. 2006).In the States, intratesticular or intra-epididymal injections of zinc arginate have been proposed to control male reproduction and avoid castration. Zinc gluconate was also successfully studied recently in the same purpose (Tepsumethanon et al. 2005).
1.2. Medical Control of Reproduction
The use of GnRH agonists has been studied by several authors, as these molecules are commercialized in some countries (Australia, New Zealand, USA...) and may well be soon put on the market in Europe. GnRH agonists act by down-regulating GnRH receptors in the pituitary, and they therefore exert a suppressive action, leading to a reversible "medical castration", without any side effects. Potential clinical application may be postponement of puberty, reduction of aggressiveness, control of fertility and control of prostatic diseases. It may also be valuable in working dogs (like guide dogs for blind or handicapped people) which could be used without being castrated and therefore may be able to mate bitches at the end of their working carrier. Deslorelin has been the most studied GnRH agonist drug in the male dog (see lecture from Pr. Stefano Romagnoli).
A review of the non-surgical methods of contraception and sterilization has just been published by Kützler and Wood (2006).
2. Recent Advances in Pathology of Male Reproductive Organs
2.1. New Descriptions
Recently, a Granulosa cell tumour of the testis was described in a spitz dog (Bontempo et al. 2005). The first case of a primary osteosarcoma of the penis bone in a 13-year-old mixed breed dog was also reported (Bleier et al. 2003). A case of an atresia of the preputial orifice in a 2-month-old puppy, with subsequent fistulous tracts, was described (Meilan 2066). In 2005, Niebauer et al. suggested that relaxin of prostatic origin may be a local factor involved in connective tissue weakening and subsequently in perineal hernia formation in old male dogs.
2.2. New Ways of Diagnosing Male Organic Pathology
Many studies have been published about the use of ultrasound to diagnose prostatic problems. Atalan et al (1999) have studied the accuracy of this technique to estimate the volume and the weight of the canine prostate. They showed that the best ultrasound predictors were the prostate width and length. Powe et al. (2004) found a strong accordance between cytologic and histopathologic diagnoses for prostatic conditions. Levy et al. (2006) recently showed that a prostate with a normal ultrasound examination may be considered as not infected. These authors also showed that, in case of a dog suffering from a "prostatic syndrome", a negative urinalysis offers a good exclusion test of prostatic infection. In case of a positive urinalysis, it is recommended to further perform a bacteriological identification after an ultrasound-guided biopsy in order to confirm the infection. Root Kustritz (2006) reviewed the indications, techniques, possible side-effects and interpretation of tissue and culture samples from the canine reproductive tract, including prostatic tissue samples. Madrigal et al (2006) also studied specific changes in the proteinogram from dog semen prostatic fractions, which may proved useful in a near future in the diagnosis of highly advanced prostate processes.
Some new approaches have also been made in the diagnosis/treatment of prostatic diseases, like the use of trans-urethral ultrasound (TUUS), which could find potential applications in prostate cancer diagnosis and staging, accurate measurement of the prostate, image guided biopsy or even in surgery of the prostate. Ultrasound also bears some perspectives in the treatment of prostatic abscesses, performing an ultrasound-guided drainage (+/- a local or general antibiotic therapy) instead of applying a heavier surgery like omentalisation.
Some authors have also studied the use of Doppler system in male genital pathology. Günzel-Apel et al. (2001) found significant changes in case of benign prostatic hyperplasia or testicular neoplasia. Agut (2004) found an increased blood flow when using colour Doppler in case of orchitis and a reduced blood flow in case of testicular torsion. The interests of computer tomography has also lead to preliminary studies, for example in diagnosing neoplasms and/or metastasis in case of retained intra-abdominal testis. This technique may also help to differentiate prostatic abscesses (ring-effect after IV administration of contrast medium) from cysts (no ring-effect). In case of prostatic abcedation, it may also help to evaluate extracapsular spreading of pus.
Masserdotti et al (2005) studied the cytologic features of testicular tumours after fine needle biopsies performed in 92 dogs. Cytology provided a sensitivity of 95% for seminomas, 88% for sertolinomas and 96% for Leydig cells tumours. The specificity was 100% for all the tumours types, thus showing that cytology is a very reliable technique.
2.3. New Treatments
When trying to reduce the volume of the prostate, some trials using anti-estrogenic drugs, such as clomifene and tamoxifen citrate, have been attempted. However, they may also induce an estrogenic response, due to their partially agonist effect. Potential applications in treatment of prostatic diseases in dogs are currently being studied by researchers. But they remain experimental at the moment.
Lévy et al. (2006) have studied the aerobic bacteria in the prostate of 45 dogs suffering from infectious prostatitis and found that most bacteria found showed a relatively low sensitivity to usual anti-infectious agents often used in veterinary medicine. In this study, overall bacterial sensitivity was best towards marbofloxacin, cefquinome and enrofloxacin.
New surgical treatments involving male genital tract have been described. In France, a debate about the use of orchidopexy in case of inguinally located retained testis has occurred. New surgical treatments of urethral prolapse in the dog has also been published.
3. Recent Advances in Male Infertility
Veterinarians are more and more often asked to diagnose and solve fertility problems in male pure-bred dogs. Still, in 2006, very little is known about male infertility in the dog.
3.1. New Discovery Concerning the Causes of Infertility
3.1.1. Prostatic Problems
The prostate is the only accessory gland present in the dog, as no seminal vesicles exist. A prostatic problem often plays a direct role in decreasing fertility. Chronic prostatitis has been shown to be a rather common cause of infertility in dog. It is often suspected when a dog brought for semen collection for Artificial Insemination or freezing of the semen suffers from haematospermia, especially in the 3rd fraction of the ejaculate. In case of haematospermia, when suspecting an infectious prostatitis, Lévy et al. (2006) showed that bacterial examination after an ultrasound-guided biopsy seems the only reliable diagnosis technique, much more than semen culture.
When treating prostatic problems in the dog, the use of common anti-androgenic compounds may definitively alter the quality of semen and subsequent fertility. That is why many reports have been made about the use of 5 α reductase inhibitors (finasteride). Finasteride is a 4-azasteroid synthetic drug that inhibits 5α-dihydroreductase, an enzyme that is responsible for the metabolism of testosterone to dihydrotestosterone in the prostate, liver and skin.
Different regimes have been proposed:
1 mg/kg daily PO for 21 weeks. Treated dogs had a marked decrease in prostate size 5-15 weeks after treatment began. The prostate size was significantly reduced (30% of the initial value) and fertility was fully restored after a20-22 weeks recovery (Iguer-Ouada 1997)
Reduced doses of 0.1 mg/kg or 0.5 mg/kg daily PO for 16 weeks have proved to be effective (43% reduction of the prostatic volume). Finasteride treatment reduced the volume of the ejaculates without affecting sperm number, sperm defects, libido or fertility after Artificial Insemination (Sirinarumitr et al. 2002).
Recently, some new anti-androgenic drugs (osaterone acetate) seemed to decrease the size of the canine prostate without altering spermatogenesis and may be potentially used in breeding dogs (Mimouni et al. 2006).
3.1.2. Retrograde Ejaculation
Retrograde ejaculation consists of a retrograde backflow of semen into the bladder when ejaculation occurs. This leads to either aspermia or oligospermia. In dogs, retrograde ejaculation is not well documented. This problem does not seem to be permanent. Treatment of retrograde ejaculation has been better documented recently (Romagnoli 2004, Beaufays et al 2004). Treatment may be attempted by collecting semen when the bladder is full (which makes the sphincter close more firmly). Sympathomimetic drugs like phenylpropanolamine (3 to 4 mg/kg per os twice daily) or pseudoephedrine (4 to 5 mg/kg per os three times daily or 1 to 3 hours before semen collection or attempted breeding) may be tried.
3.1.3. Hormonal Dysfunctions
Central hormonal causes are not well documented. Testicular tumors which are responsible for excessive hormonal secretion (Sertoli cells tumors, Leydig cells tumors) may cause a decrease of spermatogenesis, even when these tumors are located only in one testicle and still quite small in size. Hypothyroidism is often stated as a potential cause of infertility. The link between hypothyroidism and low quality semen is still unclear and probably very much overestimated.
3.1.4. Infectious Diseases
Infectious diseases probably represent a major cause of infertility in male dogs living in breeding kennels. Germs can cause prostatitis, which may alter the biochemical composition of prostatic fluids and may induce a permanent or temporary blockage of the ducts as they enter the prostate. But infections often lead to an orchitis/epididymitis, with a subsequent alteration of the quality of the semen. Canine Brucellosis infection in males have been well described and any male dog suffering from infertility with a bad spermogram should be serologically tested for this disease. Recently also, the interest of leukocytes quantification in the ejaculate has been further studied (Martin 2005).
3.2. New Diagnosis Tools
Veterinarians should be aware that in many cases of true azoospermia the size of testes remain unchanged.
In case of azoospermia, it is recommended to assay the alkaline phosphatase concentration in seminal fluid. This concentration is much higher in the epididymis than in the testes or prostate. A normal intact dog with an incomplete ejaculation usually shows a concentration of this enzyme in seminal fluid at less than 5000 units/L, because little epididymal fluid has been ejaculated. Male dogs with true azoospermia, due to causes other than bilateral blockage of the outflow tract usually have concentrations over this level. In males with bilateral obstructive azoospermia, the concentration may be very low (sometimes as less than 10 units/L).
In the case of true azoospermia, ultrasonography of testes may show tumors, or heterogeneous testicular tissue, which makes the veterinarian often believe that spermatogenesis is reduced and that the seminiferous tubes are empty. Ponzio et al (2002) have studied the interest of testicular ultrasound in evaluating fertility in the dog. In wild canids, it was shown that males with proven fertility had larger testis, a greater diameter of mediastinum testis or a parenchyma of higher echogenicity.
Testicular biopsy should be considered as among the last attempts to know the exact state of decline of the spermatogenesis. If some sperm cells (for example, spermatids) remain present inside the seminiferous tubes, the prognosis may not be desperate. In some cases, karyotype could also be evaluated.
3.3. New Treatments
Aromatase inhibitors, such as formestane, exert an anti-androgenic effect by inhibiting the conversion of testosterone into estradiol 17 β. in peripheral tissues. Recently some of these compounds (4-androsten-4-ol-3,17-dione) have been successfully used experimentally to improve spermatogenic function in oligozoospermic and azoospermic dogs (Kawakami 2003).
Intra-cytoplasmic sperm injection (ICSI) has been poorly studied yet in the dog (Fulton et al. 1998).
4. Recent Advances in Semen Processing
In the past few years, many papers have reviewed the new techniques for a precise assessment of canine semen quality and male fertility. Rijsselaere et al (2004) showed that, in case of haematospermia, the presence of up to 10% blood is not detrimental for chilling canine semen at +4°C, but is not recommended in case of semen freezing. The recovery and freezing of epididymal sperm has been successfully tried, which may be performed in recently dead dogs (post-mortem recovery). Hermansson & Linde-Forsberg (2002) and Verstegen et al. (2002) have showed that preliminary chilled semen at +4°C could further be successfully frozen, thus making it possible for veterinary practitioners to collect the semen and send it to specialised semen banks, by overnight express services, to have it frozen afterwards. The same successful study was done by Ponglowhapan et al. (2004) using epididymal sperm. Finally, the improvement of fertility after A.I. by adding prostatic fluid to respectively collected or epididymal dog semen was studied by some authors (Nöthling et al. 2005, Hori et al. 2005).
References are available upon request.