Abstract:
The growth rates between 5 and 11 months, and 11 and 17 months, of 284 ewe lambs born in the spring of 19.51, and 269 born in the autumn of 1952, were analysed. The growth rates were calculated as the differences between the logarithms of the successive body weights. The analysis of the data indicated that: (i) there is a negative correlation between the two growth rates due to environment in the two different periods; (ii) the genetic correlation between the two growth rates is zero, and it therefore appears that there are different sets of growth genes operating during the two periods of growth; (iii) the heritability for the first and second periods of growth is 0.27 and 0.31 in one group and 0.04 and 0.22 in the other group respectively. Environment therefore plays a greater part in causing variation in the growth rates than does heredity.