Die doeltreffendheid van vroeë seleksie van Merinoramme op grond van 'n seleksie-indeks

Abstract

Efficiency of early selection or Merino rams on a selection
index. Production traits of 196 unselected young Merino rams were measured at two consecutive shearings with six months' wool growth, at the age of 12 and 18 months. The correlation between repeated measurements of the same traits was about 0,60. Final selection was based on a selection index estimated from measurements of body mass, clean wool mass and fibre diameter over a 12-month period with relative weighing factors of 1: 25: -9 respectively. A similar selection index, based on the first six months' data, had a correlation of 0,84 with the final total selection index. Consequently, early selection based on an early selection index would be highly efficient. With 50% selected at the early stage and 5 - 20% at the final stage, the efficiency of selection would still be close to 100%. A simple selection index based on body mass and greasy wool mass with relative weighing factors of 1: 15 (including no data of fleece analyses) had a correlation of 0,45 with the final selection index. If 50% would be selected at the early stage according to this index, the efficiency of selection would decrease by about 5%. The results obtained were in agreement with the theory of early selection.

Prestasietoetsing is by twee opeenvolgende geleenthede gedoen op 196 ongeselekteerde jong Merinoramme wat met ses-maandewolgroei geskeer is op 12- en 18-maande-ouderdom. Die korrelasie tussen herhaalde metings van dieselfde produksiekenmerke was ongeveer 0,60. Finale seleksie is gedoen op grond van 'n seleksie-indeks saamgestel uit metings van liggaamsmassa, skoonwolmassa en veseldikte oor 'n 12-maandeperi ode met relatiewe wegingsfaktore van onderskeidelik 1: 25: -9. 'n Soortgelyke seleksie-indeks, bereken op die data van die eerste ses maande, het 'n korrelasie van 0,84 met die finale totale seleksie-indeks getoon. Gevolglik sou vroeë seleksie op grond van die vroeë seleksie-indeks 'n hoë mate van doeltreffendheid gee. Met 50% op die vroeë stadium geselekteer en 5 - 20% op die finale stadium, sou die doeltreffendheid van seleksie nog naby 100% wees. 'n Eenvoudige seleksie-indeks, gebaseer op liggaamsmassa en rouwolmassa met relatiewe wegingsfaktore 1: 15 (met geen data van vag-ontledings nie), se korrelasie met die finale seleksie-indeks was 0,45. Indien 50% op die vroeë stadium volgens hierdie indeks geselekteer sou word, sou die doeltreffendheid van seleksie met ongeveer 5% verlaag word. Hierdie verkreë resultate stem goed ooreen met die teorie van vroeë seleksie.

Keywords: Early selection, Merino rams.