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Pet Rats - Growth and Lifespan of Rats

Growth and Lifespan

Rats are born after 21-28 days gestation, although the normal term is 22-23 days. Rats have poor eyesight but their senses of hearing and smell are many times more sensitive than ours. Baby rats' eyes open when they are between 13-16 days old, although they can hear and smell a few days after birth.

Food for Baby Rats

Baby rats often start to nibble solid food as soon as their eyes open, but they still need their mother's milk until they are at least four weeks old. As with all mammals, mother's milk is the best food for young rats - they should not be weaned from the mother, or fed milk substitutes/animal formula, without good reason. Their bodies are designed to thrive on rat milk, not cat formula! There is no need to offer soft weaning foods; unlike human babies, young rats have teeth and can gnaw from the moment they start to eat solids. They do not need purees.

Cute rat walking

Leaving Their Mother

Rats normally leave their litter at 6 weeks of age; they are fully weaned from their mother at 4-5 weeks, but benefit greatly from staying with their breeder and being socialised until 6 weeks, since the period from 2-6 weeks of age is a crucial stage in the rat's mental and social development. It is important that rats are allowed to stay with their litter until this age.


Rats usually become fertile between 5-12 weeks of age, but does have been known to get pregnant as young as 3 1/2 weeks. This is only an issue if young does are introduced to older males who can mate with them; their litter brothers will not become fertile until after 5 weeks of age.

Pet rat in a pocket

If litters are not separated by sex at 6 weeks old, some does are likely to be pregnant. We are aware that most rat books say that does do not become fertile until 8 weeks old, but unfortunately, many baby female rats have not read the books, and get pregnant a lot younger than this! Such early pregnancy places a great strain upon the mother and her babies; please don't take the risk.

Rats grow rapidly until they reach 12-14 weeks. After this, the growth slows down but they continue to fill out until they reach six months of age. Adult bucks usually weigh 400-700g, does around 200-500g.

As long as a rat has been handled as a youngster, it will bond to you no matter how old it is when you first get it. Rats usually live for around two years, although some make it to three and beyond. A big cage, other rats for company, a healthy diet, and lots of exercise is the best way of making sure that your rats have a long, happy life. last updated 1 Oct, 2017


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