Elliotdale and crossbred lambs: growth rate, wool production, fat depth, saleable meat yield, carcass composition and muscle content of selected cuts

Abstract

Growth and carcass parameters were studied for 62 second-cross lambs (Poll Dorset rams over Border Leicester x Merino ewes) and 55 purebred Elliottdale lambs. Second cross lambs grew faster (P<0.001) from weaning to the first slaughter time than Elliottdale lambs and consequently weighed more and had heavier carcasses. Elliottdale lambs produced significantly (P<0.001) more wool between birth and weaning. The slope of the relationship between GR (tissue depth over the 12th rib 110 mm from the midline) and carcass weight was 1.24 � 0.23 mm/kg for second cross lambs and 0.82 � 0.17 mm/kg for Elliottdale lambs, indicating the latter lambs were leaner at heavier weights. Measures of subcutaneous fat depth at the 5th/6th and 12th/13th ribs were similar when carcass weight differences were considered for a subsample of 21 second cross and 26 purebred Elliottdale lambs. Subjective assessment of fat distribution and carcass conformation by 2 assessors revealed a significant (P<0.001) difference between breeds; second cross lambs having a better conformation. Saleable meat yield, carcass composition, and muscle content of several cuts were determined for a subsample of lambs. At a common side weight of 8 kg there was no significant difference in saleable meat yield. At this weight, crossbred lambs had a significantly (P<0.05) higher muscle content (505 g/kg) than Elliottdale lambs (480 g/kg). Fat content was similar at 300 g/kg with crossbred lambs having significantly (P<0.05) less bone (190 g/kg) than Elliottdale lambs (2 10 g/kg). The legs of carcasses from crossbred lambs were shown to contain significantly more muscle than those of Elliottdales (206 v. 195 g/kg). Carcass weight explained some of the variation in weight of leg and forequarter muscle (r2 = 0.63 and 0.61). This was improved by including an assessment for conformation from 1 assessor (r2 = 0.69 and 0.64). Eye muscle area at the 12th rib did not add significantly to the prediction; it was not different between breeds, nor was its depth to width ratio different between breeds. The pH measurements of the M. longissimus thoracis et lumborum were similar between breeds.