Reverse selection in a Japanese quail line previously selected for 4-week body weight.

After 38 generations of individual selection for high 4-week body weight in a Japanese quail line (T) fed a 20% protein diet containing .2% thiouracil, a reverse selected line (TR) was established by selecting quail in the T line with the lowest 4-week body weight. The TR line was thereafter provided with the same nutritional environment as the T line and selected for low 4-week body weight for 5 generations. The mean 4-week body weights of T line quail increased only slightly from generation 38 through 43. The 4-week body weights of the TR line, however, showed a definite downward trend. The difference in 4-week body weight between the T and TR lines in generation 43 was 15.2 g.