The growth and carcass composition of strains of mice selected for large and small body size

Abstract

The growth and carcass composition of two strains of mice (N- andC-strain), which had both been selected for large and small body size by Falconer, have been studied.Differences in body weight between mice of theN-strain and their controls were apparent at birth and were fully maintained up to 30 weeks of age. The patterns of growth were similar in all three lines, although the large line grew at a faster rate than the small line, the controls being intermediate. Differences in absolute and relative rates of growth between the three lines reach a maximum from 21 to 35 days of age and declined thereafter.Growth in the large line of theN-strain from 14 to 40 days of age was largely due to an increase in body protein and water; after this age, increase in weight was caused mainly by fat deposition. In the small line of this strain, protein, water and fat were deposited at a more constant rate during the whole growing period. Differences in rates of growth may account for the differences in the percentage composition found between mice of the large and small lines of theN-strain at the same age.