Objectives and selection criteria for Dorset sheep in Australia

Abstract

Selection objectives were defined for the Dorset breed in each of its three roles in the Australian prime lamb industry. Traits influencing returns to the prime lamb producer were identified and included in the selection objective when the Dorset is used (1) as a terminal sire (TS), (2) as part of a crossbred dam which is mated to a sire of another breed (XD) and (3) as part of a crossbred dam which is mated to a Dorset sire (XDTS). Characters used as selection criteria included those that could be recorded by breeders with different performance recording programs. Index coefficients, genetic gains in each trait included in the selection objective and the correlation between selection objectives and indices were calculated. Correlations were also calculated among the three selection objectives and among the selection indices using a certain set of selection criteria, but derived for different selection objectives. The results indicate that definition of the selection objective has only a moderate influence on the genetic gains of the traits included in the objective. The use of a single measure of liveweight as a selection criterion provided a good estimate of breeding value for objective TS but was less satisfactory for objectives XD and XDTS. Indices derived for selection objective XDTS were highly correlated with indices developed for objectives TS and XD. Thus the generalised use of indices derived for XDTS would result in negligible loss of genetic gain for objectives TS and XD. It is concluded that separate definitions of selection objectives for the three roles of the Dorset breed is not warranted. The use of selection indices developed for objective XDTS would result in little or no loss of genetic gain in the important production traits of the Dorset breed.