[Body weight dynamics of laboratory white rats in the postnatal development period]

Dynamics of body mass has been followed in 663 noninbred animals from birth up to 3.5 years of age. The rats are kept in vivarium, taking into account necessary demands upon their diet, breeding, amount of the brood and sex dimorphism. The offspring is obtained with a strictly dated time of birth. During the first month of life they are weighed daily (up to a complete maturation, specimens of both sex are measured, till intensity of males and females growth is similar), and then with the interval, increasing as a geometrical progression, with a coefficient 1.1 up to the 1231st day after birth (males only). At every period of observations no less than 7 animals are examined, average mass and standard deviation are calculated. Dynamics of the parameters are determined by means of sliding average. Using the curves on the body mass changes in the laboratory rats during nearly their whole life, it is possible with a desired precise to determined their age at carrying out investigations of wide range on ontogenesis of organs and tissues, when the animals are bred in nurseries.