Inbreeding in the Elsenburg Dormer sheep stud

Abstract

Data of the Elsenburg Dormer sheep stud which was kept closed since its inception, were collected over a period of 50 years (1941-1990). These data were analysed to monitor the increase in actual level of inbreeding and to investigate the effect of inbreeding on some early growth and reproduction traits. In total, 9 551 pedigree, 8963 birth weight and 7782 weaning weight records were available.The average level of inbreeding of all animals over all years was 15%. At the end of the study the average inbreeding coefficient in the population was 20.5% with a minimum of 18.2% and maximum of 26.3%. The regression coefficients of lamb inbreeding on birth weight (BW), weaning weight (WW), average daily gain (ADG) and Kleiber ratio (ADG/WW^0.75) were -0.008, -0.099, -0.0009 and -0.021, respectively. All these coefficients differed significantly (P < 0.01) from zero. Inbreeding of the dam had no significant effect on these traits. No significant effect of lamb or dam inbreeding on average litter size (lambs bom/ ewe lambing), survival rate (lambs weaned/lambs born) and still births was observed.

Data van die Elsenburgse Dormerskaapstoet wat geslote was vanaf oorsprong, is oor 'n periode van 50 jaar (1941-1990) ingesamel. Hierdie data is ontleed om die toename in die werklike vlak van inteling te monitor en die effek van inteling op sekere vroeë groei- en reproduksie- eienskappe te ondersoek. In totaal was 9551 stamboom-, 8963 geboortegewig- en 7782 speengewigrekords beskikbaar. Die gemiddelde vlak van inteling van alle diere oor alle jare was 15%. Aan die einde van die studie was die gemiddelde inteeltkoëffisiënt in die populasie 20.5% met 'n minimum van 18.2% en maksimum van 26.3%. Die regressiekoëffisiënt van inteling van die lam op geboortegewig (GW), speengewig (SW), gemiddelde daaglikse toename (GDT) en Kleiberverhouding (GDT/ SW^0.75) was -0.008, -0.099, -0.0009 en -0.021, onderskeidelik. Al hierdie koëffisiënte het betekenisvol (P < 0.01) van nul afgewyk. Inteling van die ooi het geen betekenisvolle effek op hierdie eienskappe gehad nie. Geen betekenisvolle effek van lam- of ooi-inteling op fekunditeit (lammers gebore/ooie gelam), oorlewingsvermoë (lammers gespeen/lammers gebore) en peri-natale mortaliteit (doodgeboorte) is gevind nie

Keywords: Dormer sheep, early growth traits, inbreeding depression, reproduction traits