GROWTH AND CARCASS CHARACTERISTICS OF FIRST AND SECOND CROSS LAMBS LOT-FED TO HEAVY WEIGHTS

SUMMARY The growth, carcass characteristics and meat quality of 75 cryptorchid lambs lot-fed for 43 days was examined. The lambs were sired by Texel and Poll Dorset rams and born to Merino or Border Leicester x Merino ewes giving 4 genotypes (TM, TBM, PDM, PDBM). The PDBM lambs grew significantly (P < 0.05) faster than the TM and PDM lambs with TBM lambs not significantly different from the other groups. A linear model (P < 0.001) best explained changes in ultrasonically measured fat and eye muscle depth over the feeding period. There was a significant difference (P < 0.05) between genotypes for fat depth measured over the eye muscle (Fat C) and at the GR site. Both the TM and PDM lambs produced significantly (P c 0.05) leaner carcasses than their second cross equivalents when adjusted to a carcass weight of 28.5 kg. The dimensions or area of the eye muscle were not affected by genotype, but the TBM lambs had the lowest EUROP score (or best conformation) and the PDM the highest, the difference being significant (P < 0.05). Genotype had no significant effect on L* (relative lightness) or a* (relative redness) values of the eye muscle. TM and PDM carcasses had significantly higher bl* (relative yellowness) values (tail fat) than TBM carcasses and at the 12th/13th rib site the TBM carcasses also had significantly (P c 0.05) lower b2* values. First cross (TM and PDM) lambs will be leaner at heavier weights, providing a saleable meat yield advantage over second cross lambs, but from the limited sample of sires used no advantage of Texel sired lambs over Poll Dorset sired lambs was evident.