The use of selection indices for merino sheep:

An index selection scheme for Merino sheep is proposed. It is recommended that for the preliminary selection of young replacement material all available animals should be classed subjectively for breed characteristics and serious defects and that not more than l0% be culled at this stage. For rams the following traits should then be measured objectively: body mass in kilograms(X₁), clean wool mass in kilograms (X₂), fibre diameter in microns (X₃) and fold score (X₄). Each of these traits are then given a relative weight which is of the order of l:7:-l:-l respectively. The index for the selection of rams then becomes: 1 = lX₁+ 7X₂– lX₃– lX₄. For ewes the traits body mass in kilograms (X₁), greasy wool mass in kilograms (X₂), crimps per 25 mm (X₃) and fold score (X₄) are measured objectively. The index for the selection of ewes is: I = lx_l + 4X₂+ lX₃ –lX₄ Rams and ewes with the highest index values are then selected.