Rats are able to breed throughout the entire year when the conditions are suitable. The female can produce five litters every year and the gestation period is only 21 days. The litters may be up to 14, but most of the time they are around seven. They can reach sexual maturity in five weeks under the ideal conditions.
Rats can breed quickly and they do not recognize incest between them, so the son can mate with the mother or brothers with their sisters. There is no set breeding season, but too cold or very hot temperatures may reduce the breeding season. Rats may come into heat every five days unless they are nursing or pregnant. Menopause in rats starts at the age of 18 months and the cycle will start to be irregular until it stops completely. However, the rat can still get pregnant and give birth to a low number litter.
Rats can breed when they are put together during the heat period, but this could be challenging since the since the female may fight off the male. A rat in heat will open its vagina as it is normally closed. It will also give some signs like stroking its back that may lead to the mating dance. It may spin around and dart forward, and it will brace its legs stiffly, lift the head and the tail, and vibrate the ears. This is the display that shows the male that the rat is ready to mate. In the right conditions, a rat can mate with multiple males up to 500 times in a six hour period. This means that females of certain species such as the brown rat can produce up to 2000 babies a year.
The male will get interested at once and will sniff and lick her. During the mounting, it can grasp the scruff using its teeth. In the courtship, the mounting can occur many times, but most of them will only be for foreplay. The female is able to become pregnant after being mounted just once. When the female is not in heat, a persistent and determined male may make her come into heat. The females that are in heat may even escape their cage to find the male. The rat may go into heat again 24 hours after giving birth, but it is not good for her to get pregnant again so quickly.
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