Selection for economic characters in Australian Merino sheep. II. Relative efficiency of certain aids to selection.

Abstract

Theoretical consequences of the use of progeny testing, sib testing, and mass selection are examined in a flock of 1,000 ewes producing 700 progeny of breeding age each year. Selection based on a combination of individual merit and merit of half-sibs should result in approximately the same annual improvement as that achieved by optimum use of progeny-tested sires. In large flocks extensive use of outstanding sires by artificial insemination may increase progress for traits with heritability of about 0.3 by a factor of about 1.2 as compared with mass selection. The advantages to be gained by progeny testing and artificial insemination may be outweighed by the dangers of inbreeding, and the cost involved would have to be considered. As most of these advantages should be achieved by combination or even by mass selection, which avoid inbreeding and much of the cost, progeny testing with wide use of progeny-tested sires is unlikely to be the most economical road to flock improvement.