Selection for crimp frequency in the wool of Merino sheep. 1. Direct response to selection

Abstract

Two selection flocks consisting of 100 ewes mated to five rams were established at the Agricultural Research Station, Trangie, in 1950. One flock was selected for high crimp frequency (Crimps Plus), and the other for low crimp frequency (Crimps Minus). Responses in these flocks were measured against a randomly selected control flock maintained in the same environment and with the same management. The Crimps Plus flock showed a steady increase in crimp frequency with realized heritabilities of 0.46 ¦ 0.14 for ewes and 0.38 ¦ 0.15 for rams, calculated over five generations of selection. In contrast, response in the Crimps Minus flock was not linear as there was a large response in the first generation but very little after that. Dam-offspring heritabilities calculated for sheep entering the flocks after the first generation were 0.40 ¦ 0.14 for the Crimps Minus flock and 0.47 ¦ 0.15 for the Crimps Plus flock. It is suggested that prior selection in the base population may have resulted in unequal gene frequencies, and hence the reduction of response in the Crimps Minus flock. No satisfactory explanation could be given for the large response to the first generation of selection in this flock.