Female pigs do not have periods in the same way women do; instead, they have an estrous cycle characterized by signs of heat, such as a swollen, reddened vulva, but they do not experience the outward bleeding of the uterine lining that occurs during menstruation. The lining of a pig’s uterus is reabsorbed, a process different from the shedding seen in a menstrual cycle.

What pigs do experience (Estrous Cycle)

Behavioral and physical changes: Pigs enter a period called “heat” (estrus) where they become sexually receptive to mating.

Signs of heat: You may observe a swollen, reddened vulva, mucus discharge, restlessness, vocalization (like high-pitched whining), mounting other pigs, or a “standing” reflex where the female stands rigid and immobile when mounted.

Key differences from human menstruation

No outward bleeding: A significant difference is the lack of visible bleeding from the vulva.

Internal process: In female pigs, like other mammals that don’t menstruate, the uterine lining is reabsorbed internally at the end of the reproductive cycle.

Menstruation is rare: True menstruation, with visible bleeding, is a relatively rare phenomenon found primarily in primates and a few other specific species.

Immediate veterinary care is needed for a sow that is still bleeding weeks after giving birth. A small to moderate discharge in the first few days after farrowing is normal, but prolonged or heavy bleeding is a serious symptom of an underlying medical problem.

Potential medical causes
Prolonged postpartum bleeding can be a symptom of several conditions, including:

Retained afterbirth or fetus: If part of the placenta or a mummified piglet remains inside the uterus, it can cause infection and persistent bleeding.

Uterine infection (metritis): Bacteria can enter the uterus during farrowing, causing an infection that results in large amounts of foul-smelling discharge, which may include blood. Metritis is often accompanied by fever, lethargy, and a loss of appetite.

Vulval or uterine trauma: The vulva or uterus can be injured during a difficult or assisted birth. A severe vulval hematoma (blood-filled swelling) can occur, and if it ruptures, it will cause heavy bleeding.

Uterine prolapse: Though usually happening within hours of farrowing, a prolapse can sometimes occur later. This is a life-threatening condition where the uterus turns inside out and protrudes from the body, causing significant blood loss.

Cystitis (bladder infection):

Infections of the bladder or kidneys can lead to blood or pus in the urine, which may be mistaken for a vaginal discharge.

What to do immediately
Contact a veterinarian immediately. Prolonged bleeding is a serious issue that requires a professional diagnosis and treatment. In some cases, it can be life-threatening.
Monitor the sow closely. Take note of her behavior and any other symptoms, as this information will be vital for the vet.

Appetite: Is she eating and drinking normally?

Energy level: Does she appear lethargic or weak?

Fever: Is she unusually warm to the touch? A fever can indicate a severe infection.

Milk production: Is there a drop in milk production? Reduced milk supply is often an early sign of a problem.

Piglets: Are her piglets showing signs of being underfed, such as weakness or diarrhea?

Provide supportive care. Keep the sow in a clean, quiet, and comfortable environment to minimize stress and prevent further infection.

Do not attempt manual intervention. Unless you are a vet or experienced in such a procedure, you risk causing further injury, shock, or infection.