Effects of crossbred ewe genotype and ram genotype on lamb carcass characteristics from the lowland sheep flock

Abstract

A study was carried out on five lowland farms in Northern Ireland over 2 years to investigate the effects of crossbred ewe and ram genotype on lamb carcass characteristics. Four ewe genotypes were sourced from six hill farms – Bluefaced Leicester×Blackface (BLXB), Texel×Blackface (TXB), Suffolk×Cheviot (SXCH) and Texel×Cheviot (TXCH). On each farm groups of 20 to 30 of each crossbred ewe genotype were crossed with Suffolk or Texel sires. Within each of the ram breeds, high lean growth index rams sourced from UK sire reference schemes (SRS) were compared with rams sourced from flocks not involved in objective genetic improvement programmes (control). Throughout the 2 years of the study the ewes lambed at 1 and 2 years of age. Lambs from each of the crosses were slaughtered at 36, 44 and 52 kg live weight. Assessed on a 5-point scale, lambs from BLXB ewes had the poorest conformation classification values (2.8) (P<0.001) compared with 3.0–3.2 (S.E. 0.051) for lambs from the other ewe genotypes. Lambs from TXB, SXCH and TXCH ewes had similar conformation classification values. The differential in conformation classification values between lambs from BLXB ewes and those from the other genotypes was greater when the ewes were crossed with Texel (0.6 units) compared with Suffolk rams (0.3 units) (P<0.05). Differences in conformation between the sire breeds varied according to ewe genotype (P<0.05). When crossed with BLXB ewes there was no difference between Texel and Suffolk-sired lambs in terms of conformation classification values (2.7 v. 2.8 (S.E. 0.07), while with all the other ewe genotypes, Texel-sired lambs had a significantly higher conformation classification than Suffolk-sired lambs (3.5 v. 3.0 when crossed with T×B; 3.2 v. 2.9 when crossed with SXCH; 3.4 v. 3.0 when crossed with TXCH (S.E. 0.07)). Sire reference scheme-sired lambs had greater growth rates from birth to slaughter (203 g/day) compared with control-sired lambs (193 g/day) (S.E. 3.7 days) (P<0.05) and were of an improved conformation classification (3.1 v. 3.0 (S.E. 0.04)) (P<0.01). There was a significant interaction (P<0.01) between ram breed and ram source on lipid content of the carcass. Within the Suffolk-sired lambs, there was no significant difference between SRS-sired lambs (197 g/kg) and control-sired lambs (190 g/kg) (S.E. 6.2 g/kg). However, within the Texel-sired lambs, SRS-sired lambs had a lower lipid content (174 g/kg) than control-sired lambs (204 g/kg) (S.E. 6.2 g/kg) (P<0.01).