Thesis (PhD(Agric))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This study set out to determine (co)variance components for the important production, reproduction and conformation traits of a South African fine wool resource flock that was established at the request of the South African wool industry. A secondary aim was to assess progeny of these animals under pastoral conditions in areas where the production of fine wool is uncommon. The Cradock fine wool Merino stud was established in 1988 with ewes bought from producers with the finest clips in South Africa. Data collected from 1988 to 2010 were used to estimate the (co)variances for the genetic fine wool resource flock. The quantification of the interdependencies of fibre diameter (FD) with production, reproduction and subjective traits were the main objective of this study. It is evident from the results of this study that FD is a highly heritable (0.63 ± 0.03) trait, which can lead to marked genetic progress provided that there are adequate levels of phenotypic variation available during selection. Fibre diameter was unfavourably correlated with body weight (0.30 ± 0.05), clean fleece weight (0.24 ± 0.05) and reproduction (0.59 ± 0.18), which implies that selection for reduced FD can have a detrimental effect on all these traits. Despite these unfavourable genetic correlations genetic gain in the other economical important traits was achievable in the stud (-0.129 ± 0.033). These results were supported by the results obtained during the evaluation of progeny of this stud under pastoral conditions where the production and reproduction of the fine wool animals were comparable with medium wool animals. It can therefore be concluded that selection for reduced FD can be practiced without detrimental effects on the economically important traits and subsequently the profitability of the sheep enterprise, as long as breeders have a reasonable selection objective based on economic considerations. / AFRIKAANSE OPSOMMING: Hierdie studie het dit ten doel gehad om (ko)variansie komponente vir die belangrike produksie, reproduksie en subjektiewe eienskappe in 'n Suid-Afrikaanse fyn wol hulpbronkudde, wat gevestig is op versoek van die Suid-Afrikaanse wolbedryf te bepaal. 'n Sekondêre doel was om die nageslag van hierdie diere onder veldtoestande te evalueer in gebiede waar die produksie van fynwol ongewoon is. Die Cradock fynwol Merino stoet is in 1988 gestig met die aankoop van ooie van produsente met die fynste skeersels in Suid-Afrika. Data wat ingesamel is vanaf 1988 tot 2010 is gebruik in die bepaling van (ko)variansie komponente vir hierdie genetiese fynwolkudde. Die kwatifisering van die interafhanklikheid van veseldikte (VD) met produksie, reproduksie en subjektiewe eienskappe was die hoofdoel van die studie. Dit is duidelik uit die resultate van die studie dat VD `n hoogs oorerflike (0.63 ± 0.03) eienskap is, wat tot vinnige vordering in VD kan lei indien genoegsame fenotipiese variasie beskikbaar is tydens seleksie. Veseldikte is ongunstig gekorreleer met liggaamsgewig (0.30 ± 0.05), skoonvaggewig (0.24 ± 0.05) en reproduksie (0.59 ± 0.18), wat beteken dat seleksie vir ʼn verlaagde VD nadelige vordering in hierdie eienskappe tot gevolg kan hê. Ten spyte van hierdie ongunstige genetiese korrelasies was die genetiese vordering in die ekonomies belangrike eienskappe haalbaar in die kudde wat ondersoek is (- 0.129 ± 0.033). Die laasgenoemde resultate word ondersteun deur die bevindinge dat die nageslag van hierdie stoet se produksie en reproduksie ooreengestem het met medium wol diere onder veldtoestande. Die gevolgtrekking wat gemaak kan word uit die studie is dat VD verlaag kan word sonder nadelige gevolge in die ekonomies belangrike eienskappe, asook die van `n skaapboerdery onderneming. Om dit te vermag moet telers `n aanvaarbare benadering tot seleksie, gegrond op ekonomiese beginsels, volg.