The Reproductive Mysteries of Guinea Pigs: Do They Get Periods?

All female mammals have a uterus, and piggy sows are no exception. Since guinea pigs can become pregnant from as early as two months of age, owners may wonder if they can expect any physical changes during heat cycles. Menstruation occurs in humans and a handful of other species, so it is natural to wonder if guinea pigs also get periods.

Female guinea pigs do not get periods, but they do experience estrous cycles. If fertilization does not occur at the optimal time, the lining of the uterus, called the endometrium, is reabsorbed by the animal’s body. Bloody discharge is never normal, and it indicates a health issue.

Owning female piggies does not involve treating period pains, sugar cravings, or extra cage cleaning. Let’s learn more about the cavy heat cycles and the possible cause of any unusual discharges you may notice.

Do Female Guinea Pigs Bleed On Their Period?

Menstruation is a process that only occurs in a tiny number of mammals. Female humans share this physical trait with monkeys, chimpanzees, a few species of bats, and elephant shrews. 98% Of mammal species, including guinea pigs, do not menstruate.

The start of menstruation, or periods, in human females and a few other animals is a natural process and a sort of coming of age. It indicates that the reproductive system has reached maturity.

Female guinea pigs reach reproductive age very young. Sows become sexually mature when they are between 55 and 70 days old! Fortunately, their bodies aren’t quite the same as mammals that experience periods.

Female mammals of all species either have menstrual or estrous cycles. One results in periods, and the other does not. Guinea pigs fall into the category that has an estrous cycle, which is colloquially called being on heat.

An estrous cycle is not the same as a menstrual cycle, which results in regular periods. Female guinea pigs do not bleed since they never shed the endometrial lining of their uterus. If fertilization does not occur during the heat cycle, the sow’s body reabsorbs the lining, and it is not released as a discharge.

Guinea pigs experience spontaneous heat, and ovulation periods can happen up to five times a year. Some things you should know about a female piggy’s estrous cycle:

  • It can happen at any time of the year but is more common during spring.
  • The length of the cycle is 16 days.
  • The female is fertile for between 6 to 11 hours in each cycle, most often at night.
  • Cycles occur spontaneously, and there are no set intervals between each heat.
  • A new estrous cycle begins soon after a female piggy has given birth.
  • There should not be any bloody discharge while a piggy is on heat.

Do Guinea Pigs Have A Monthly Cycle?

Ovulation in female guinea pigs is spontaneous and can happen at any time of the year. Therefore, they do not have monthly cycles and don’t menstruate.

The first heat cycle usually happens when a young sow is around two months old. Cavies are polyestrous animals, meaning they can go into heat several times each year.

Take note that female cavies are not permanently in heat. Estrous cycles occur spontaneously up to five times a year and more often in spring.

A guinea pig sow will be on heat for 16 days. If owners are responsible, and fertilization does not occur, the uterus lining will be reabsorbed, and life will continue as usual. There will not be any menstrual period at the end of the heat cycle.

How Can I Tell If My Guinea Pig Is In Heat?

Although some cavy sows display some behavioral signs when they are in heat, others do not. Some signs that your piggy is in estrous may include:

  • Appearing a little moody or irritable
  • Chasing cage mates
  • May become agitated and appear restless.
  • Trying to mount other piggies.
  • Swaying of hips or rear end
  • She may make more frequent low-rumbling vocalizations.

Even though a guinea pig on heat may show classic behavioral signs that she is on heat, the window period for actual mating is less than 12 hours. There is no need to treat your female guinea pig differently while on heat. She will likely appreciate it if you are extra patient and loving if she seems a bit grumpier than usual.

How Long Do Female Guinea Pigs Get Periods?

Spiny mice and elephant shrews are the only known rodents that get menstrual periods. Guinea pigs, like hamsters, rabbits, and most other mammals on earth, experience estrous cycles and never get periods.

A normal cavy estrous cycle is approximately 16 days long and results in no discharge. Cycles are spontaneous and can come on at any time of the year. A guinea pig of either gender, with any sign of blood on its private parts, requires immediate veterinary attention.

Why Is My Guinea Pig Bleeding From Her Bottom?

Since female guinea pigs don’t get periods, bleeding is never normal. No matter how old or young your piggy is, a veterinarian must check unusual discharges as soon as they are noticed since they can be a sign of something serious.

Blood on your piggy’s private parts could be caused by several conditions, including:

  • Conditions affecting the ovaries or uterus.
  • Bladder stones – This serious condition is relatively common in cavies. It is extremely painful and can result in bloody urine.
  • Urinary tract infection – Dark-colored urine may resemble blood. The discharge may be coming from a piggy’s bladder rather than its uterus.
  • Tumors in the urinary tract or reproductive system – Internal growths can bleed or irritate the area they are attached to, which can result in the animal passing blood.


Only a tiny percentage of mammals on earth have periods, and guinea pigs are not part of this select club. Like cats and horses, cavies are polyestrous, which means they experience heat cycles that occur spontaneously several times a year.

If fertilization does not occur, the uterus’s endometrial lining is simply reabsorbed into the animal’s body. Any blood on a cavy is not menstrual and must be considered a medical emergency.