Genetic and environmental trends of early growth traits in the Elsenburg Dormer sheep stud

Abstract

Data from the Elsenburg Dormer sheep stud were used to estimate genetic and environmental change in early growth traits from 1943 to 1990. Best linear unbiased predictions (BLUP) of breeding values were obtained by Restricted Maximum Likelihood (REML) procedures fitting a direct additive and maternal additive genetic model. Environmental change, calculated as the difference between phenotypic and genetic values, was found to be negative for all traits studied. Genetic trends were smaller but significantly positive. The higher maternal trends reveal that the biggest genetic improvement was in the additive genetic ability of ewes to produce faster growing or heavier lambs. The relative low but linear genetic trends suggest that selection pressure on these traits was low during the 48 years, probably owing to higher selection emphasis on traits other than the growth traits studied.

Data van die Elsenburg Dormerskaapstoet is gebruik om die genetiese en omgewingsveranderinge in vroeë groeieienskappe vanaf 1943 tot 1990 te beraam. Beste lineêre onsydige beramers (BLUP) van teelwaardes is verkry deur Beperkte Maksimum Aanneemlikheid(REML)-prosedures deur 'n model wat direkte additiewe sowel as mateme additiewe waardes as toevallige effekte ingesluit het. Omgewingsveranderings, bereken as die verskil tussen fenotipiese en genetiese waardes, was negatief vir al die eienskappe. Genetiese tendense was kleiner maar betekenisvol positief. Die hoër tendense vir maternale waardes dui daarop dat die beste genetiese vordering gemaak is in die additiewe genetiese vermoë van ooie om vinniger-groeiende of swaarder lammers te lewer. Die relatiewe lae maar lineêr-betekenisvolle genetiese tendense dui aan dat seleksiedruk op hierdie eienskappe baie laag was gedurende die afgelope 48 jaar, moontlik as gevolg van hoër seleksiedruk op ander eienskappe as groei- eienskappe.

Keywords: Dormer sheep, early growth traits, genetic and environmental trends.