Diminished discrimination in Merino genetic evalutations.

Many Merino studs use across-year Best Linear Unbiased Predictor (BLUP) evaluations performed with incomplete pedigree but with common sires providing links between successive years commonly in the form of linked sire evaluations. Simulation results are presented which show that sire-only pedigree structures under BLUP analysis lead to significant underestimation of the genetic differences between years. This would have some impact on the efficiency of selection across age groups, and would cause severe underestimation of genetic trends within a flock. An optimal solution to this problem is also likely to be found by such simulation studies.