CHAPTER 39 The Reproductive Tract
Sexual Differentiation
TABLE 39-1 Timeline of sexual differentiation in canine fetuses*
Gestational age (Post-LH surge) | Sexual differentiation |
---|---|
32 days | Female and male gonads undifferentiated |
36 days | Ovarian differentiation first detected in female embryos |
36 days | Testicular differentiation first detected in male embryos |
36 days | Müllerian duct regression in male embryos first observed |
42 days | Wolffian duct regression in female embryos first observed |
46 days | Müllerian duct regression in male embryos completed |
46 days | Wolffian duct regression in female embryos completed |
* Differentiation of fetal gonads and internal genitalia occurs between 32 and 46 days of gestation relative to the maternal preovulatory luteinizing hormone (LH) surge.
Canine and feline male external genitalia originate from an undifferentiated urogenital tubercle (which forms at the level of the embryonic cloacal membrane). As a direct result of the influence of DHT, the prepuce develops from a circular plate of ectoderm invaginating at the level of the distal tip of the penis, whereas the junction between the preputial and penile mucosa (balanopreputial fold) dissolves at a later stage, also as a direct result of the action of androgens. In the absence of DHT (as in the normal female), the caudal vagina, vestibule, and vulva develop. Determination of gender in newborn dogs and cats may be difficult because the difference at this age is a slightly longer anogenital distance in males (13 to 15 mm) versus females (7 to 8 mm) (Figure 39-2). A pseudohermaphrodite is an animal that has the gonads of one sex with the internal and/or external genitalia and/or the chromosomal complement of the opposite sex (Box 39-1).
Testicular Descent

Figure 39-3 The normal relationship between the vaginal process, epididymal ligament, and gubernaculum.
(Redrawn from Peter AT: The reproductive system. In Hoskins JD (ed): Veterinary pediatrics: dogs and cats from birth to 6 months, ed 3, Philadelphia, 2001, Saunders, pp 463-475.)
Puberty
TABLE 39-2 Onset of puberty in the normal bitch and queen of reported breeds
Species/Breed | Age at pubertal estrus |
---|---|
Canine | |
Beagle | 7.2-23 months |
Labrador Retriever | 7.2-16.3 months |
Mongrel | 6.3-17.1 months |
Feline | |
Abyssinian | 7-14 months |
Birman | 10-18 months |
Burmese | 4-19 months |
Himalayan | 4-16 months |
Manx | 9-18 months |
Siamese | 4-20 months |
Domestic Shorthair | 4.5-15 months |
Domestic Longhair | 6-18 months |
Modified from Johnston SD: Premature gonadal failure in female dogs and cats, J Reprod Fertil Suppl 39:65-72, 1989.
Reproductive Disorders in Male Pediatric Patients
Testicular Abnormalities

Figure 39-4 Sample karyotype form.
(Reproduced with kind permission from Drs. B.P. Chowdhary (Director) and T. Raudsepp (Associate Director) of the Molecular Cytogenetics Laboratory at the College of Veterinary Medicine and Biomedical Sciences, Texas A&M University.)
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