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Determination of Patient Sex and Spay-Neuter Status

Brenda Griffin

Sex Determination

Physical examination should always include determination or verification of each patient's sex. Obviously, this is essential in the context of spay-neuter programs. Wise clinicians never assume a patient is the sex they have been told, but instead always make that determination for themselves prior to performing surgery. Verifying the animal's sex, as well as assessing their reproductive status, informs and prepares the surgeon for the appropriate procedure. It may also prevent him/her from attempting to spay a male calico cat.

Sexing Dogs

Determining the sex of a dog is generally straightforward and can almost always be quickly accomplished through physical examination, including simple visual inspection of the external genitalia. In this species, the male and female anatomy are distinct and easy to identify, even in the case of very young patients. In female dogs of all ages, the vulva is readily identified on the ventral midline in the caudal inguinal area between the hind limbs (Figure 1.1a and b). It consists of two thick folds of tissue (called the labia pudenda or vulvar lips), which form a rounded commissure dorsally and a pointed commissure ventrally, producing a tear-drop shape. The vertical slit-like opening between the two labia (known as the vulvar cleft) marks the external orifice of the urogenital tract. Of note is that a fold of skin surrounds the canine vulva. In young puppies, the vulva is small and somewhat recessed in this fold (referred to as an "infantile" or "juvenile" vulva), but becomes increasingly prominent as the pup develops and attains puberty.

In male dogs, both the penis and the scrotum are readily identified on the ventral midline. The penis, encased in its prepuce or sheath, is located in the mid abdominal region caudal to the umbilicus, while the scrotum lies in the caudal inguinal area between the hind limbs (Figure 1.2a and b). Although minimal hair is present in the inguinal region of young puppies, within a few months the prepuce generally becomes well covered by hair, while the scrotum becomes increasingly pendulous. In puppies the testicles descend into the scrotum very soon after birth, usually within the first several days, and are typically palpable by two to four weeks of age depending on the pup's size (Ley et al. 2003). By the time a male puppy is presented for castration (i.e. at six weeks of age or older) both testes should be present in the scrotum and, if not, a tentative diagnosis of cryptorchidism should be made. Although relatively uncommon, testicular descent is sometimes delayed. Later descent is possible because the inguinal canals do not close until the time of puberty, usually around 5-10?months of age depending on the individual dog. Although late descent of one or both testicles is possible during this time frame, it may not be desirable to postpone castration (Griffin et al. 2016).

Figure 1.1 External genitalia of a female puppy (a) and adult dog (b). Note the tear-drop shape of the vulva, which is located in the caudal inguinal area between the hind limbs.

Figure 1.2 External genitalia of a male puppy (a) and adult dog (b). The penis is encased in a sheath (called the prepuce) and the testicles lie within the scrotum. Note that the adult dog's prepuce is well covered with hair and the scrotum is much more pendulous than that of the male puppy.

In dogs, the reported prevalence of cryptorchidism ranges from 0.8 to 10%, with the highest rates often occurring in certain breeds, including Chihuahuas, miniature schnauzers, Pomeranians, toy and miniature poodles, Shetland sheepdogs, Yorkshire terriers, boxers, and German shepherd dogs (Yates et al. 2003; Birchard and Nappier 2008). Despite the fact that cryptorchidism is one of the most frequently recognized congenital defects in small animal practice, it is not necessarily the most common reason that one or both testicles are not readily palpable in the scrotum of young puppies. In fact, a more common reason might be temporary retraction into the inguinal area. Indeed, when the testicles are not readily palpable in the scrotum, it may not indicate that a puppy is truly cryptorchid; rather, it may simply be a function of the fact that small, slippery testicles can easily escape detection during examination because they sometimes retract into the inguinal area when digital pressure is applied. Furthermore, it is possible for one or both testicles to slip back through its respective external inguinal ring into the canal or abdomen. This can occur in awake patients, and in the author's experience it occurs even more commonly when a pediatric puppy is anesthetized and placed in dorsal recumbency. If the testicles are absent from the scrotum on palpation, lifting the patient into an upright position often allows the "missing" testicle(s) to descend back into its proper anatomic location in the scrotum. This can be done by holding the puppy gently around the chest to support its body weight, taking care to support the head and neck if needed, while allowing the hind limbs to gently hang down (Figure 1.3a-c). Alternatively, with the puppy in dorsal recumbency, gentle continuous digital pressure may be applied to "smooth" down the soft tissue of the groin, beginning in the area of the inguinal rings and continuing caudally toward the scrotum; this action will usually push the missing testicle(s) back into the scrotal sac (Figure 1.4a-c). These techniques can be used to locate testicles that "disappear" from the scrotum and help the surgeon avoid unnecessary exploration for the gonads. Whenever possible, the goal should be to verify that both testicles are present in the scrotum prior to surgery, so that the surgeon can plan accordingly if cryptorchidism truly exists. For information on surgical castration of cryptorchid dogs, see Chapter 14.

Sexing Cats

In contrast to dogs, determining the sex of cats can be more challenging, particularly in the case of small kittens. Unlike dogs, where the external genitalia of both sexes are readily visible in the inguinal (groin) area, the external genitalia of male and female cats are located in the perineal region beneath the tail. The small size of the species' penis and vulva, combined with the fact that these structures are generally well covered by hair, further complicates their identification. Upon inspection, the penis is not visually obvious in tomcats at any age and, prior to weaning age, the presence of the testicles in the scrotum is usually not visually apparent either. Although present in the scrotum at or within a few days of birth, the testes are simply too small to be either visually apparent or easily palpable in the first few weeks of life. Although the feline penis never becomes visually obvious, the testes do quickly become larger as kittens grow and are increasingly readily visible beneath the anus by six to eight weeks of age. Usually by the time of a kitten's first veterinary visit, the testicles are readily palpable in the scrotum (Griffin 2006). If one or both testicles is absent, a diagnosis of cryptorchidism is highly likely: delayed or late testicular descent is possible but very uncommon in cats. The reported prevalence of cryptorchidism is relatively low in cats (<2%), although much higher rates have been reported in the Persian breed (Millis et al. 1992). As is the case in pediatric puppies, care must be taken to ensure accurate examination, because gentle digital pressure applied during scrotal palpation may cause small testicles to temporarily slip into the inguinal region, where they may elude detection. The techniques previously described for returning such testicles to their proper anatomic location in the scrotum can be used for kittens as well as puppies. Notably, the absence of testicles following neutering can also make sexual determination of a tomcat difficult for untrained observers.

Figure 1.3 (a-c) Holding a puppy upright in this position with the hind limbs hanging down may allow the testicles to descend back into their proper anatomic location within the scrotal sac (a). Initially, the left testicle was retracted back into the inguinal area proximal to the scrotum (b), but it quickly reappeared in the scrotum when the puppy was held in this position (c).

Figure 1.4 (a-c) With the puppy in dorsal recumbency, the soft tissue of the groin can be digitally "smoothed" down from the area of the inguinal rings toward the scrotum in order to gently push the testicles back into the scrotal sac.

Careful inspection of the perineal area is necessary in order to determine the sex of a cat or kitten. For adults, an individual's overall body type and/or appearance may sometimes suggest the cat's sex. For example, many male cats are larger in stature with heavier bones than female cats, and most calico cats are females (Figure 1.5). That said, such characteristics should never be used to determine sex without concurrent inspection of the perineal area. When there are no obvious testicles present, visual inspection of the perineum focuses on evaluating the distance between the anus and genital opening, as...