How do rats reproduce?

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Rats, like other rodents, have developed a very successful and prolific breeding strategy. They are highly social animals, they take care of each other and, although the males do not have a very developed parental care, the females do help each other to be able to raise all the offspring..

In this AnimalWised article we will tell you How do rats reproduce, how are the reproductive cycles of females and males and how is the development of the offspring after birth.

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  1. Sexual behavior and factors that affect
  2. Reproductive system and cycle of the male rat
  3. Reproductive system and cycle of the female rat
  4. Development of rats after birth

Sexual behavior and factors that affect

Sexual behavior appears during puberty. Males reach this stage at 6 weeks of age and females between 6 and 8 weeks after birth. The behavior is dimorphic between females and males, that is, they have a different sexual behavior according to the sex to which they belong. Males have active reproduction throughout their lives and, on the other hand, females only accept to copulate when they are in heat or estrus..

Sexual behavior is regulated by hormones and is affected by environmental factors:


Female rats are annual polyesters, in other words, they can reproduce all year round if the appropriate lighting conditions are met (12 hours of light and 12 hours of darkness). In nature, these conditions do not occur during the winter months, so during this time the birth rate is very low. In captivity, domestic rats do reproduce all year round, without reducing the number of heats or offspring, as long as we provide them with adequate light / dark cycles..

If we talk about the rat as a pet, we must also take into account the intensity of light, as high intensities can produce eye damage, especially if we talk about albino rats.


Animals with a small size, such as rats, badly withstand extreme temperatures, whether they are low or high. Due to the surface / volume ratio of their body, they poorly regulate these temperatures. In periods of the year when the temperature is very high or low, anestrum is produced in the females and they will not go into heat, therefore, they will not reproduce.

Nutritional condition

During pregnancy, a increase of certain components on the diet, but overeating is always harmful. It has been shown that a caloric restriction before heat can improve fertility and possibly lengthen the reproductive life of the female. Vitamin deficiency can cause infertility, especially vitamins A, E, B2 and B1.

Presence or absence of the opposite sex

The presence of the opposite sex favors the appearance of sexual maturity. In contrast, absence inhibits maturity, especially when there is a dominant male.


Pheromones are crucial when it comes to establish relations among rats. Not only do they mediate the reproductive cycles, they also provide information on the hierarchy within the group, health status, fertility, etc..


Rats are very sensitive animals. In the wild, they may decide to leave the nest for a safer one, but in captivity, noises and even strong smells (such as perfume) can cause high levels of stress, leading to suppression of heat or cannibalism of the young..


Overcrowding only occurs in captive rats, therefore, we must ensure that we offer our pets a cage with the appropriate dimensions. If the rats are crowded they will not reproduce, as the females will enter anestrum.

Reproductive system and cycle of the male rat

The male rat reaches puberty when it is 6 weeks old, but will not reproduce until it reaches 10 or 11 weeks old, At this point, it will be able to reproduce throughout its life.

The reproductive system of male rats is very similar to that of other mammals. It consists of a penis, two testicles, the accessory glands, and the tubes that carry sperm to the outside. In the testicles, we find structures called the head, body and tail of the epididymis through which the developing sperm will pass as they mature and the seminiferous tubules, where the sperm are created.

The spermatogonia (male germ cells) are formed from cells in the seminiferous tubules of the testes. Each spermatogonia can produce up to 120 sperm. These sperm develop during their passage through the epididymis, going through several phases:

  1. Primary spermatocyte
  2. Secondary spermatocyte
  3. Spermatid
  4. Spermatozoon

Upon reaching the tail of the epididymis, the sperm will be fully developed and the ability to fertilize an egg is achieved by joining the seminal fluids produced by the accessory glands. This cycle of sperm creation and maturation lasts 13 weeks approximately.

As we said, the reproductive system of male rats is very similar to other mammals, with two exceptions:

  • They have clotting glands, which allow the clotting of ejaculated semen that plugs the entrance to the vagina, which is known as a vaginal plug.
  • The prostate is double instead of simple, with a ventral and a dorsal zone.

Reproductive system and cycle of the female rat

Like most quadruped females, they present bicornuate uteri (uteri with two horns) located on both sides of the abdomen. They also have two ovaries, vagina, clitoris and vaginal entrance.

Females reach puberty between 6 and 8 weeks old, but will not reproduce until 10-14 weeks. They are annual polyestric, so they have jealousy throughout the year and these last between 4 and 5 days. As in other mammals, the heat of rats consists of 4 phases: proestro, estrus, metaestro and right-handed.

  • Proestro: lasts about 12 hours, the vulva thickens slightly and the vagina is dry. May accept male, but fertilization will not occur.
  • Oestrus: lasts 14 hours. The vulva is completely swollen (vulvar swelling) and the vagina is dry. It will accept the male and lordosis will occur, that is, the female will acquire a curved position of the spine. If there is copulation, we can observe the vaginal plug, which serves as a reproductive strategy to prevent another male from trying to copulate with the female and thus ensure their own offspring. This plug dissolves naturally in less than 12 hours after copulation.
  • Metaestro: lasts for approximately 21 hours. The vulva begins to lose thickness. Ovulation occurs and the female will not accept the male.
  • Right handed: it is the longest phase and lasts 65 hours. The vulva returns to its normal state and the vagina is moist. Does not accept the male.

If fertilization does not occur during the cycle, the female will suffer a pseudopregnancy, which will last between 12 and 14 days. If fertilization occurs, the gestation it will last between 21 and 23 days.

Development of rats after birth

Female rats may have litters of 6 to 15 young. Young at birth are completely dependent on their mother, weigh about 3 or 5 grams, are deaf and blind, pink in color and have no hair. We can know that they are newborn because there will be no milk in the stomach, in less than 12 hours after birth we will see a white color in the belly, it corresponds to a stomach full of milk.

When the young are 7 days old, their skin will begin to be covered by a fine and soft coat of hair. Ear canals begin to open and ears separate from head.

At approximately 2 weeks, they will open their eyes, some open them earlier than others and do not have to open both at the same time. At this age they will begin to investigate the nest, they will even be able to leave, although the mother will continually return them to the shelter.

From the 21 days old, the cubs will go weaned gradually, they will begin to take solid food, gain independence and learn everything necessary for adult life.

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