Male Anatomy

The reproductive tract of the male or tom cat consists of the penis, testes, scrotum, prostate and bulbourethral glands, and the ductus deferens (also called the vas deferens) (Figure 39-1). The fetal testes are inside the abdomen; they descend through the inguinal ring into the scrotum at birth or shortly afterward. By 6 to 8 weeks of age, testes should be palpable in the scrotum. The hair-covered scrotum is divided by a thin wall into two cavities; each cavity contains a testis, epididymis, and the end of the spermatic cord. The testes may not stay in the scrotum permanently until 4 to 6 months of age. The structure of the feline testis is similar to most domestic animals.⁹ There are three major cell types in the testes:

FIGURE 39-1 Anatomy of the reproductive tract of the male cat.

(From Johnston S, Root Kustritz M, Olson P: Sexual differentiation and normal anatomy of the tom cat. In Johnston S, Root Kustritz M, Olson P, editors: Canine and feline theriogenology, Philadelphia, 2001, Saunders.)

Production of spermatozoa occurs in seminiferous tubules; spermatozoa are then transported into the epididymis, where maturation and storage takes place. The seminiferous tubules are closely packed and convoluted and are surrounded by interstitial cells. The tail of the epididymis becomes the ductus deferens, which carries sperm to the penis after passing through the inguinal canal with the rest of the spermatic cord. The spermatic cord consists of the ductus deferens, the testicular artery and vein, lymphatics, and nerve plexus.

The prostate of the cat is approximately 1 cm in length and covers the urethra near the neck of the urinary bladder. The prostate is androgen-dependent and atrophies after castration. Prostatic disease is very rare in the cat, with only a few cases reports of tumors published.^38,39 The bulbourethral glands are two small pea-shaped structures near the bulb of the penis. During ejaculation, spermatozoa from the epididymis are mixed with secretions from the prostate and bulbourethral glands. It is normal for a small proportion of spermatozoa to travel retrograde through the urethra into the bladder (Figure 39-2). The urethra in the male cat is very narrow and shorter than in the dog.

FIGURE 39-2 Because a degree of retrograde ejaculation is normal in the tom cat, collection of a urine sample after ejaculation allows for detection of sperm.

The penis of the cat contains a vestigial os penis (5 mm in length). When not erect, the penis is completely enclosed within the prepuce. The glans of the penis of a mature tom cat is covered with 120 to 150 penile spines that are directed caudally. The spines are testosterone-dependent and start to appear at about 12 weeks of age, are fully developed at puberty, and are absent in neutered males, disappearing by about 6 weeks after castration (Figure 39-3).

FIGURE 39-3 A, Glans of the penis of an intact tom cat with penile spines. B, Glans of the penis of a castrated cat without penile spines.

In addition to testosterone, important hormones in the male cat include LH and FSH, both produced in the anterior pituitary gland in response to gonadotropin-releasing hormone (GnRH), produced by the hypothalamus. Resting plasma testosterone levels vary widely, because secretion is episodic. Testosterone is not only essential for development of secondary sexual characteristics (e.g., heavy jowls, thick skin) and breeding behavior but also for production of spermatozoa. Castration causes an immediate drop in blood testosterone, but viable sperm may still be present for up to 7 weeks after surgery.

Mating Behavior

Spermatozoa are present in the testes by the age of 5 to 9 months, and full maturity of spermatogenesis occurs at 8 to 10 months of age.³⁷ However, the actual age at which mating begins varies with physical condition, body size, and season. The onset of puberty is typically at 8 to 10 months of age and at a body weight of 2.5 kg or more. However, significant variation among breeds is seen with longhair breeds, such as the Persian, maturing more slowly than shorthair breeds, such as the Siamese. Tom cats probably have a normal breeding lifespan of 10 years or more.

Tom cats are attracted to estrous queens by vocalizing, odors, and behavior. A tom cat will approach a queen in estrus, touch noses, and then investigate her perineum. A flehmen reaction may be exhibited, that is, sampling of the queen’s pheromones by the vomeronasal organ. The tom cat grasps the skin on the back of the queen’s neck and attempts to mount her. The tom cat then treads on his back feet and slides down over the back of the queen, attempting to position for intromission. The tom cat starts a series of pelvic thrusts, and ejaculation follows within 20 to 30 seconds. Semen is deposited in the posterior vagina. The tom cat then quickly jumps away to avoid being swatted by the queen. Once the queen’s postcoital behavior settles down (typically in 10 to 60 minutes), the tom cat will often try to grasp and mount again. A pair may breed several times until the tom cat is exhausted. Breeding usually occurs at night under natural circumstances.

After castration, mating behavior typically ceases, but may persist for years in some mature and experienced tom cats. The behavior may include mounting of other cats or kittens, the owner’s legs, or soft inanimate objects. It is important to ensure the cat is not cryptorchid (see below). A rare cause of breeding behaviors in castrated male cats is a testosterone-secreting adrenal tumor.²⁵ The behavior may be attention seeking or because of a stimulus-poor environment. Ensuring adequate environmental enrichment and interactive time with the owner is often helpful. The behavior should not be rewarded, even inadvertently, by attempts at punishment. Interruption and distraction with another activity is likely to be more effective. Urine spraying may also persist after castration, although typically it resolves in 80% or more of cats. There is one report in the literature on the use of cyproheptadine (2 mg/cat, PO, every 12 hours) for the successful treatment of masturbation and urine spraying in a cryptorchid cat.³² For more on urine spraying, see Chapter 13.

Control of Reproduction

Vasectomy

Vasectomy involves the bilateral removal or occlusion of a portion of the ductus deferens, causing infertility by preventing ejaculation of sperm during copulation. Vasectomy does not remove or prevent undesirable sexual behaviors, because testosterone is still produced. Therefore it is infrequently used for control of reproduction in male cats. However, “teaser tom cats” (infertile males with good libido) may be used in catteries to bring queens out of heat when pregnancy is not desired. Mating with a teaser tom cat induces a pseudopregnancy in the queen and delays return to estrus. Vasectomy does not alter libido or mating ability in adult tom cats. Live sperm may be present for up to 7 weeks after surgery, however.³⁰

Vasectomy is a relatively simple surgical procedure performed through a 1- to 2-cm incision cranial to the scrotum (Figure 39-4).¹⁴ After incision of the skin and subcutaneous tissue, the spermatic cords are identified and exteriorized from the tunica vaginalis using blunt and sharp dissection. Gentle manipulation of the testicle is helpful for identification of the spermatic cord. Once the ductus deferens is isolated, a small segment is removed and the severed ends are ligated. The subcutaneous tissue and skin are closely routinely.

FIGURE 39-4 Vasectomy. A, After incision of the skin and subcutaneous tissue, the spermatic cord is identified. B, The spermatic cord is exteriorized from the tunica vaginalis using blunt and sharp dissection. C, Once the ductus deferens is isolated, a small segment is removed and the severed ends are ligated.

Diseases and Conditions of the Penis

Few problems affect the penis of cats; conditions found more commonly in other species, such as hypospadias and persistent penile frenulum, are rare in the cat. One case report of hypospadias in a 1-year-old Himalayan cat was associated with chronic cystitis.¹⁷ The hypospadias was surgically corrected and the cat recovered fully. A 1-year-old Persian cat presented for infertility was found to have dorsal deviation of the penis resulting from a persistent frenulum.¹

A small number of cases of phimosis have been reported in the cat.^4,10,22 Phimosis is due to constriction of the preputial opening that prevents protrusion of the penis. Phimosis may be congenital or acquired secondary to trauma, inflammation, or neoplasia. The most common clinical signs are stranguria, pollakiuria, and vocalizing during urination²²; other clinical signs include dribbling urine, urinating outside the litter box, and inability to mate. The severity of clinical signs varies with the degree of narrowing. Diagnosis is made on physical examination. In many cases, surgical correction of the defect is necessary.

The records of 10 cats diagnosed with phimosis at Michigan State University Veterinary Teaching Hospital have been reviewed.²² The mean age at presentation was 18.6 weeks (range, 8 weeks to 2.4 years). Two of the cats had other congenital defects (cryptorchidism, penile hypoplasia). Eight of the 10 cats underwent surgical correction of the condition by a full thickness incision in the ventral aspect of the prepuce, with or without resection of a wedge of prepuce. A satisfactory outcome was achieved in seven cats, where long-term follow-up was available. Congenital phimosis has been reported in an 8-week-old domestic shorthair cat presented for hematuria, pollakiuria, and polydipsia.⁴ Urine culture was positive for E. coli. Surgical correction of the phimosis was accomplished by resection of a small wedge of the dorsal prepuce, and along with antibiotic treatment, led to resolution of clinical signs.

Priapism is persistent abnormal erection of the penis in the absence of sexual stimulation, and may be caused by a variety of factors, such as spinal cord injury, trauma, neoplasia, and inflammation. It is rarely reported in the cat. Priapism may be confused with paraphimosis; however, paraphimosis is associated with a narrow preputial orifice or other preputial abnormalities. Without intervention, the penis may become dry and edematous, and even necrotic. Most cases in the cat require surgical management. In a series of seven cases of priapism, six cases were in Siamese cats.¹¹ In four of the cases, priapism developed after unsuccessful attempts at mating, despite the fact that three of the cats were castrated. Five of the cats were successfully treated with perineal urethrostomy, and histologic examination revealed thrombosis of the corpus cavernosum.

Priapism was reported in a 1.5-year-old domestic shorthair cat after routine castration.³⁶ Two days after surgery, the cat developed pollakiuria and stranguria, as well as protrusion of the penis. The cat was successfully treated with perineal urethrostomy. Histology of the resected tissue revealed severe congestion of the corpus cavernosum, with organized thrombi and areas of necrosis. Another case of priapism was reported in a 2-year-old castrated cat with feline infectious peritonitis (FIP).^31a At necropsy histologic examination of the penis revealed severe pyogranulomatous inflammation and fibrinoid necrosis of the corpus cavernosum.

Diseases and Conditions of the Testes

Few conditions of the testes of the cat come to the attention of clinicians, with the exception of cryptorchidism. Other problems that are occasionally encountered include orchitis, neoplasia, and abnormalities of gonadal sex or chromosomal sex.

Orchitis is rare in the cat, although occasionally bacterial orchitis has been reported. Clinical signs include scrotal swelling, pain, and redness. Bacterial orchitis is treated with a broad-spectrum antibiotic for 2 to 3 weeks. Orchitis has also been reported as an uncommon manifestation of FIP⁸; one case report was a cat concurrently infected with FIV.³⁴ Scrotal swelling may be the only sign associated with FIP in affected cats, at least initially (see Figure 33-16). The vaginal cavity around each testis is confluent with the peritoneal cavity so that fluid accumulated in the abdomen may also appear in the scrotum. Lesions in the testes are consistent with a chronic necrotic and fibrinous orchitis and fibrinous periorchitis with vasculitis.

Testicular neoplasia is uncommon in the cat. Examples of both Sertoli and interstitial cell tumors have been reported.^2,26,29,38 Neoplasia of testicular origin developing after castration has been reported in five cats.⁶ All cases involved interstitial cell tumors within the scrotal skin or the spermatic cord. All cats were castrated at 1 year of age or younger, and the mean age at diagnosis of the neoplasia was 9.6 years. Affected cats demonstrated sexual behaviors associated with intact males, such as urine spraying and aggression. Two cats had penile spines. The study authors suggest that care be taken during castration to avoid incising the tunica albuginea to avoid transplantation of small amounts of testicular tissue, and the subsequent development of tumors.

Testicular hypoplasia and infertility may be seen in male tortoiseshell or calico cats. It has been estimated that about 1 in every 3,000 tortoiseshell or calico cats is male.¹⁵ A survey of over 4,500 male cats in the United Kingdom determined that 0.43% were tortoiseshell.¹⁸ Orange is a sex-limited coat color in cats, controlled by a single gene on the X chromosome. Black and orange color may occur together in the female, but normally would not occur together in the male. Males exhibiting black and orange coat color may have various chromosomal abnormalities, such as 39/XXY, mosaicism (two populations of cells with different genotypes from one fertilized egg), or chimerism (two or more populations of cells from the fusion of different embryos). Mosaics or chimeras are often fertile.

Both true hermaphroditism and pseudohermaphroditism are very uncommon in the cat. Many cases are unreported, because karyotyping is not widely available for cats. Affected individuals may be discovered at the time of surgical sterilization. For example, the author has examined a blue tabby intersex cat (Figure 39-5). The cat was presented as a female and was spayed without incident. Several months later, the owners complained of a strong smell to the urine, and on examination, a small penis-like structure was present in the vulva and one testis was found subcutaneously near the vulva. The cat’s specific condition was not determined, because karyotyping and gonadal histopathology was not performed.

FIGURE 39-5 A, External genitalia of an intersex cat presented for ovariohysterectomy that was subsequently found to have one testis next to the vulva. B, A small penis-like structure was present in the vulva, and one testis was found subcutaneously near the vulva.

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