Rats begin their lives after just 20 – 30 days of gestation. Once born they cannot rely on their eyesight too much as rats don’t have the best eyesight in the world. Instead, they tend to rely on their sense of smell and hearing which are both orders of magnitude more sensitive than ours. In fact, their eyes only open after 13 – 16 days old but they are able to both hear and smell just a few days after being born.
They start eating solid food right away but also keep breastfeeding up to 4 weeks old. Like all of us mammals, they need their mother’s milk and this is by far the best food for them. It’s best to let this natural mother/offspring relationship continue uninterrupted as it’s important, not only for their nutrition, but for their mental development as well. Try and avoid weaning them on milk formula as much as possible. They do not need soft foods since they have teeth from birth and can start gnawing at things right away.
Rats tend to leave the litter at around 6 weeks of age and are weaned from their mother at 4 to 5 weeks. The period of 2 – 6 weeks of age is the most crucial in terms of development for rats so it’s really important that they are allowed to be with their litter until this age.
Rats usually become fertile between 5 and 12 weeks old but they can get pregnant as early as 3.5 weeks. Litters should be separated by sex at 6 weeks old otherwise the chances are high that some does will get impregnated. Does becoming pregnant at a very young age places a lot of stress on the mother and the babies so it’s not worth risking it. Up until around 13 weeks, does grow in size rapidly. This growth sharply tapers off soon after but they do continue to grow up until around 6 months old. An adult buck will usually weigh between 400 and 700 grams while does will weigh about 200 to 500. Rats will learn to bond with you at almost any age given enough touch and handling. They live to about 2 years old but some have been known to live up to 3 or even 4 years on rare occasions. Rats need play time, a good diet, a large cage, other rats to play with and exercise and they will be the happiest little guys around.