MATURE SIZE AND MATURING RATE IN ROC57BL 6 AND RONMRI LINES OF MICE/

In mammals, between-species correlation between mature size and maturi ng rate is high. The within-species relationship is not so clear. An e xperiment with 167 mice of small RoC57BL/6 and large RoNMRI lines was set up, to study the influence of anima mature size on maturing rate. The body mass of animals Nas measured even; 3 days, between the ages 1 2 and 120 days. Individual ages at half the adulthood and at adulthood were determined on the basis of logistic growth curves. Three linear statistical models based on an allometric equation were used to test b etween-line, between-sex-line, and between-family maturing rates. Grow th rate and maturing rate are within the species significantly affecte d by mature size. At mature size, the smaller RoC57BL/6 mice were olde r than the larger RoNMRI mice. In the model with the significant affec ts line, sea and family included, the same allometric coefficient was positive. The model which includes an allometric equation within line and sex was no better fitting than the previous model. Nor all the est imates of allometric coefficients were within expected ranges, but sta ndard errors were relatively high. Because significant effects are par tly of genetic origin and standard errors are high, the selection for higher maturing rate might be possible without changes in mature size. No method for determining degree of maturity during growth has been f ound so far, therefore the selection would be relatively slow, due to the extension of generation interval.