REPRODUCTIVE PERFORMANCE OF BOOROOLA × FINNISH LANDRACE AND BOOROOLA × SUFFOLK EWE LAMBS, HETEROZYGOUS FOR THE F GENE, AND GROWTH TRAITS OF THEIR THREE-WAY CROSS LAMBS

and was related to the level of prolificacy. Lamb mortality at birth was high in BFL (23.7%) compared to BS, FL and S (6.5, 0.0 and 0.0%, respectively, P < 0.001). Litter size at weaning (50 d of age) averaged 1.9, 1.8, 1.5 and 1.3 for BS, BFL, FL and S ewe lambs (BS vs. S, P < 0.02). Growth performance of H-sired progeny from the four genetic groups of ewes showed that H x S lambs had the highest average daily gain in both preweaning and postweaning periods (preweaning ADG: 349.9 g d '; postweaning ADG: 332.1 g d ') while the other genotypes of lambs performed equally (preweaning ADG 267.4,249.5 and246.8 g d ' for H x FL. H,x BFL and H x BS, respectively; postweaning ADG: 281.2, 276.8 and 281.8 g d ' for the same genetic groups). Overall productivity of ewe lambs in terms of kilograms of lamb produced showed a slight, nonsignificant, advantage for Booroola-cross ewe lambs (55.8 and 54.5 kg for BS and BFL) overpurebred S (51.6 kg) andFL(44.9 kg). These results indicate that ovulation rate and litter size can be increased by incorporating F gene in both prolific (FL) and nonprolific (S) background genotypes without resulting in any significant difference in total weight of lamb produced per ewe.