Rats | Breeding


Filed in Small Animals, Rats

Sexually mature rats must be properly paired to breed successfully. A single male rat may be included in a cage with one or more female rats without difficulty. More than one male and female rat may be housed together for breeding purposes within the same enclosure without risking aggressive displays.

Sexually mature rats exhibit a prominent scrotum. Sexually mature female rats exhibit a prominent double row of nipples.

Breeding Rats

Female rats should not be bred before 65 days of age. They are continuously polyestrous, which means they come into heat at regular intervals of four to five days throughout the year, unless they are pregnant or nursing.

The period during which the female is receptive to the male is about 12 hours in duration, and usually occurs at night. Females can come back into heat within 48 hours after giving birth to a litter. This is called a postpartum estrus. This period of receptivity is not used with breeding rats because the breeding male is removed from the enclosure just before the female delivers her litter because of the high probability of injury to the new pups by the male.

After mating, a white, waxy substance is visible within the female's vulva for 12-24 hours. It is not uncommon to find these plugs within the enclosure after they have been discharged.

Pregnancy lasts an average of three weeks. Litter sizes average 6-12 pups, thought it is not unusual for a female's first litter to be smaller in number. Litter sizes decrease as breeding females age. Do not disturb rats for the first two to three days after giving birth. Pups are weaned at about three weeks of age.

Irving Street Veterinary Hospital (San Francisco, CA) materials were used as an information source for this article.

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