Growth Curves for Body Weight of the Laboratory Rat

Body weight growth of rats, bred and reared in small cages, occurs in two main stages, which overlap to a degree. During the first stage, when rats develop to maturity, all parts of the animal (e.g. head, body, limbs, tail) grow, resulting in high relative growth rates. During the second stage, one of post-maturity growth, there is an increase in body weight, unaccompanied by corresponding significant changes in such measures as limb and tail length. It is thought that the increase in body weight during the second stage is due to an increase in body fat; however, further experimentation is required to verify this contention.