An analysis of postnatal growth in OF1 mice within an interval of 1-220 days of age.

The body weight growth of OF1 mice, both females and males, from day of birth to 220 days old is studied herein. After comparison of different theoretical models, an extension of Koops's multiphasic functions, the tetraphasic, is proposed as the best choice in so wide a time interval in mouse development. This function has allowed us to take into account different aspects of growth. Coefficients and phases of this function are characterized. The end of the first phase was established at 17 days of age. The second phase finished at 35 days of age in females and at 39 days in males. This difference increased during the third phase: the end of it was at 173 days of age in males, and at 160 days in females. The end of the fourth phase in OF1 mice would be produced after 220 days of age. Inflexion points in every four phases, in females and males, are situated. The biggest weight increase occurred in the second phase in both sexes, specially in males (1.26 g per day). Biological meanings of every phase are also discussed. The short lifetime of rodents have allowed us to study a great number of growth phases in a short period of time. Thus the present analysis could be a good starting point for the study of growth curves in other species of mammals.