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

Abstract

Reproductive performance of Booroola × Finnish Landrace (BFL, n = 19) and Booroola × Suffolk (BS, n = 18) ewe lambs heterozygous for the F gene were compared to Finnish Landrace (FL, n = 14) and Suffolk (S, n = 26) purebred controls. FL lambs reached puberty earlier (211.3 d, P < 0.001) than the other genetic groups (237.8, 233.0 and 232.9 d for S, BS and BFL, respectively) whereas weight at puberty was lower (P < 0.001) for BFL, FL and BS (36.8, 36.7 and 47.0 kg, respectively) than for S (61.1 kg). About 95% of BFL and BS ewe lambs had at least one record of three ovulations or more over the first three estruses, including puberty. Mean ovulation rates at breeding (second estrus after puberty) to a Hampshire (H) ram were 3.8, 3.3, 2.2 and 1.7 for BFL, BS, FL and S, respectively (BFL and BS vs. FL and S, P < 0.001). The corresponding litter sizes at birth were 2.5, 2.1, 1.6 and 1.3 (BFL and BS vs. FL and S, P < 0.001) which reflected a higher embryonic loss in the Booroola crosses. Percentage ova loss ranged between 32.8% (BFL) and 12.8% (S) 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 × S lambs had the highest average daily gain in both preweaning and postweaning periods (preweaning ADG: 349.9 g d−1; postweaning ADG: 332.1 g d−1) while the other genotypes of lambs performed equally (preweaning ADG: 267.4, 249.5 and 246.8 g d−1 for H × FL, H × BFL and H × BS, respectively; postweaning ADG: 281.2, 276.8 and 281.8 g d−1 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) over purebred S (51.6 kg) and FL (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. Key words: Sheep, ewe productivity, Booroola, ovulation rate, crossbreeding