Relationships between Growth Rate, Dressing Percentage and Carcass Composition in Lambs

Abstract

Growth and carcass measurements of 244 lambs from grade Rambouillet and Dorset × grade Rambouillet ewes sired by Dorset, Hampshire or Suffolk rams were used to study the relationships between growth rate, dressing percentage and carcass composition when slaughtered at 45 to 48 kilograms. When breed of sire influenced growth rate, carcass composition was not necessarily changed. Generally, Dorset-sired lambs grew slower, had less bone, more fat and higher dressing percentages than Suffolk-sired lambs. Hampshire-sired lambs tended to show a growth pattern similar to Suffolk-sired lambs but were similar to Dorset-sired lambs in carcass composition. Ram lambs, with their higher growth rates, had less fat and more bone in the carcass and lower dressing percentages compared with wether and ewe lambs. Singles were much heavier than twins at birth and weaning but singles grew at rates similar to the twins from weaning to slaughter. Although the single lambs were 3 weeks younger than twins at slaughter, carcasses were very similar in composition. The singles had .56% more bone than twins (P<.1). The associations between measures of growth and carcass composition, on a within breed, sex and rearing type basis were generally very low. Among the measures of growth, only birth weight had significant correlations with the percentages of bone, lean or fat in the carcass (P<.01). Weaning weight had a low correlation with the percent of bone in the carcass while postweaning average daily gain did not have any signifigant association with carcass composition. Generally, associations between measures of growth rate and carcass composition were too low to be of any predictive value when lambs were slaughtered at about 45 to 48 kg weight. Weaning weight was positively associated with dressing percentage, while postweaning average daily gain showed a negative association with dressing percentage (P<.01).