A parametric analysis of the growing CFHB (Wistar) rat

Measurements of body weight and body, tail and hindlimb lengths were made at various times during the postnatal development of the CFHB-Wistar rat using simple techniques which avoided unnecessary stress being applied to the animal. All the graphical relationships studied using these measurements indicated that growth was divided into two phases which meet at 16 days. This was particularly noticeable when either body length or hindlimb length was plotted against either age or body weight. Body weight appeared to be a better indication of maturity than time; and linear relationships were found when measurements of body lengths were plotted against the square root of body weight. Curvilinear graphs were obtained when body weight was plotted on alternative scales. Results suggest that prior to 16 days metabolism is probably directed more towards attaining sufficient maturity to enable the animal to survive independently, than to increasing its stature; but after 16 days this situation is reversed.