Van Wyk, J. B.Delport, G. J.Cloete, S. W. P.Swanepoel, Jan Willem2016-01-062016-01-062006-052006-052006-05http://hdl.handle.net/11660/2019English: Genetic (co)variances for yearling body weight (BW), clean fleece weight (CFW) and mean fibre diameter (MFD) in the SA Dohne Merino population were estimated using records of 107 389 animals recorded between 1992 and 2004. The data include records of 1 530 sires and 45 178 dams. An animal model with direct and maternal additive, maternal permanent and temporary environmental effects was fitted for all traits. Sire-flock (SF) and sire-flock-year-season (SFYS) was included as additional random effects. Fixed effects were (FYSSM) (1594 classes), type of birth (singles, multiples), age of dam (2 to 7+ years) and average age (± SD) at measurement fitted as a linear covariate (385 ± 12 days). Estimates obtained by single -trait analyses were used as starting values in three-trait analyses. The direct genetic heritability estimates for FD, CFW and BW obtained from the three-trait analysis were 0.447 (0.009), 0.216 (0.008) and 0.277 (0.008) respectively. The genetic correlations were 0.050 between BW and CFW, 0.100 between BW and FD and 0.139 between FD and CFW. The phenotypic correlations were 0.318 between BW and CFW, 0.129 between BW and FD and 0.180 between FD and CFW. Direct genetic correlations of BW, CFW and MFD were positive, which suggest that selection for bigger and heavier sheep would generally lead to a stronger MFD and higher CFW. Because these values are very low the subsequent effect of this phenomenon would be that the effect of selection for body traits on fleece traits would be very small and vice versa. Genetic trends were calculated using the annual average breeding value estimates (EBV) for each trait. According to the genetic trends derived, the selection policy followed did cause genetic change in the traits studied, even though it was slow. The level of inbreeding (F) in the South African Dohne Merino sheep population is very low. The proportion of animals that was inbred to some extent increased from 0% (average F=0) in 1980 to 38% in 2003 (average F=1.22%). No significant inbreeding depression on BW, CFW and MFD could be found. In general the results suggest that inbreeding at present is not a serious problem in the South African Dohne Merino breed.Afrikaans: ‘n Analise van die Dohne Merino skaapras in Suid Afrika is gedoen. Die data dateer vanaf 1992 tot 2004. Genetiese parameters van onderskeidelik groei- en woleienskappe vir 12 tot 14 maande oue diere is beraam. Veseldikte (VD), skoon vaggewig (SVM) en liggaamsgewig (LM) inligting van 107 389 diere wat 1 530 vaars en 45 178 moers insluit, was beskikbaar vir ontledings. Benewens direkte genetiese-, maternale genetiese- en omgewingseffekte, is vaar-kudde en vaar-kudde - jaar-seisoen effekte as addisionele toevallige effekte ingesluit. Die waardes wat bereken is uit enkel-eienskap analises is gebruik as beginwaardes vir die drie - eienskap analises. Die beraamde direkte oorerflikhede van die drie-eienskap analises was 0.447 (0.009) vir VD, 0.216 (0.008) vir SVM en 0.277 (0.008) vir LM. Die genetiese korrelasies tussen LM en SVM was 0.050, 0.100 tussen LM en VD en 0.139 tussen VD en SVM. Die fenotipiese korrelasies tussen LM en SVM was 0.318, 0.129 tussen LM en VD en 0.180 VD en SVM. Genetiese korrelasies tussen LM, SVM en VD was positief, wat ‘n aanduiding is dat seleksie vir ‘n groter dier kan lei tot sterker wol en ‘n swaarder vag. Omdat hierdie waardes baie laag is, sal die gevolglike gekorreleerde effek van seleksie vir groei-eienskappe op woleienskappe baie laag wees en vice versa. Genetiese tendense is verkry deur die gemiddelde voorspelde teelwaarde (VTW) per jaar vir elke eienskap te bereken. Uit die genetiese tendense is dit duidelik dat seleksie gebaseer op teeltdoelwitte, daargestel deur die Genootskap, wel genetiese vordering in al drie eienskappe getoon het , alhoewel vordering baie stadig was. Die vlak van inteling in die Suid Afrikaanse Dohne Merino populasie is tans laag. Produksie en reproduksie vlakke sal dus nie negatief deur inteling beinvloed word nie. Die persentasie diere wat tot ‘n sekere mate ingeteel is, het gestyg van 0% (gemiddelde F=0%) in 1980 tot 38% (gemiddelde F=1.22%) in 2003. Geen betekenisvolle inteeltverval kon gevind word nie. Die resultate dui daarop dat inteling tans nie ‘n ernstige probleem in die Suid Afrikaanse Dohne Merino skaapras is nie.enDohne Merino sheepFibre diameterBody weightGenetic parametersInbreedingClean fleece weightMerino sheep -- South Africa -- Dohne -- GeneticsSheep -- Breeding -- South Africa -- DohneDissertation (M.Sc.Agric. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2006Genetic- phenotypic- and environmental trendsDissertationUniversity of the Free State