The pig vulva is an external anatomical feature of female pigs, crucial for reproduction. Its appearance provides insights into a sow’s physiological state, offering visual cues for reproductive cycles and overall health in pig husbandry.
External Anatomy
The pig vulva, the external opening of the female pig’s reproductive tract, is located below the anus. It appears as a rounded, wrinkled structure with two fleshy lips, or labia, meeting at dorsal and ventral commissures. In gilts, young female pigs, the vulva is generally smaller and less pronounced than in older sows.
Vulva size varies, with mean lengths of 4.9-5.9 cm and widths of 1.8-2.1 cm in pubertal pigs. The ventral commissure often conceals the clitoris, a structure of erectile tissue. The external genitalia also contain connective and fatty tissues, with few hairs present.
Role in Reproduction
The pig vulva serves two primary biological functions within the reproductive process: facilitating mating and acting as the terminal exit point during farrowing. During copulation, the vulva is the external orifice through which the boar’s penis enters the female reproductive tract for semen deposition. The cervix, located internally beyond the vagina, is the site where semen is deposited during natural mating or artificial insemination.
During farrowing, the vulva becomes part of the birth canal, serving as the passageway for piglets to exit the sow’s body. As farrowing approaches, the vulva and vagina enlarge and relax to accommodate piglet passage. This physiological change supports a successful birth, enabling uterine contractions to push piglets out.
Observing Reproductive Readiness
The pig vulva’s appearance changes throughout the sow’s reproductive cycle, indicating readiness for breeding or farrowing. During proestrus, the period before estrus (heat), the vulva typically swells and reddens. This change, often more pronounced in gilts, results from increased estrogen stimulating blood flow and fluid retention. Swelling and reddening can begin 2-5 days before breeding receptivity, peaking and subsiding 24-36 hours before standing heat.
As the sow enters estrus, a clear, watery discharge may be observed from the vulva, becoming sticky and thick as estrus progresses. The clitoris may also become more prominent and red. Additionally, the vulva may appear more relaxed. These changes are important for identifying the optimal breeding time, as accurate estrus detection helps achieve high farrowing rates.
Leading up to farrowing, the vulva exhibits distinct changes, often 10-14 days before birth. During the last week of gestation, the vulva may become swollen, red, and relaxed, signaling approaching parturition. A slight mucous discharge may also be visible on the vulva’s lips hours before the first piglet is born. These visual signs, combined with behavioral changes, indicate the sow’s progression towards giving birth.