THE POSSIBLE GENETIC-IMPROVEMENT OF REPRODUCTION AND SURVIVAL RATE INAFRINO SHEEP USING A THRESHOLD-MODEL

The objective of this study was to estimate heritability and breeding values on the underlying scale for different reproductive traits and s urvival rate in Afrino sheep to ascertain whether they can be improved by selection on estimated breeding values obtained under a threshold model. Data collected on the Carnarvon Afrino flock over the period 19 69 to 1994 were analysed by means of a GFCAT set of programmes. The re productive traits analysed included fertility (whether a ewe lambed or not; 0 or 1), litter size (number of lambs born to a ewe mated; 0, 1, 2 or 3), fecundity (number of lambs born to a ewe that lambed; 1, 2 o r 3), number weaned (number of lambs weaned to a ewe mated; 0, 1, 2 or 3) and survival rate from birth to weaning (whether a lamb born alive , was dead or alive at weaning; 0 or 1). Heritabilities on the underly ing scale of 0.20, 0.27, 0.42, 0.19 and 0.02 were estimated for the re spective traits. The results suggest that reproduction rate, but not s urvival rate, can be increased in Afrino sheep by selection on breedin g values estimated on the underlying scale applying a threshold model.