ESTIMATION OF GENETIC-PARAMETERS FOR LITTER SIZE IN SHEEP USING A NONLINEAR METHOD

Variance components and breeding values were calculated for litter size in three breeds of sheep, using non-linear (GFCAT) and linear (REML, BLUP) models. GFCAT heritabilities ranged from 0.09 to 0.27, with heritabilities on the outward scale which were fairly similar to the REML estimates. REML heritabilities and repeatabilities ranged from 0.00 to 0.10 and from 0.00 to 0.20, respectively. Correlations between breeding values of rams obtained by BLUP and GFCAT ranged from 0.91 to 1.00. Correlations between breeding values of daughters and rams estimated by the two methods were fairly consistent within breed. It was concluded that rams could and should be evaluated by the more justified GFCAT method, and because of the similarity between results of the two types of methods that ewes should be evaluated by BLUP until non-linear methods can be performed with an animal model.