Genotype and age effects on sheep meat production. 5. Lean meat and fat content in the carcasses of Australian sheep genotypes at 20-, 30- and 40-kg carcass weights

Leanmeatand fat content of Australiansheep genotypes were comparedat20-,30- and 40-kg carcass weights. Sheep comprised Poll Dorsetgrowth ·Border Leicester Merino (PDg ·BLM), Poll Dorsetgrowth ·Merino (PDg ·M), Poll Dorsetmuscling ·Merino (PDm ·M), Border Leicester ·Merino (BL ·M) and Merino ·Merino (M ·M) genotypes. Lambs wereraisedasamixedflockundergrazingandslaughteredat4,8,14and22monthsofagewitheachslaughtertimeinvolving ~150mixed sex animals. At 24h after slaughter, chilled carcasses were halved along the backbone and the right sides were usedfordeterminationoflean,fatandashpercentagesusingdualenergyX-rayabsorptiometry.Withinaparticularagegroup andgenotype,animalsgrowingatfasterratesandreachingheaviercarcassweightshadlowercarcassleanmeatcontentthan slowergrowinganimals.Merinocarcassesweighing20and30kghadsimilarlevelsofleanmeattoPD ·Mgenotypes,which wasgreaterthanthatfromtheBL ·Mgenotype.Second-crossPD ·BLMcarcassesweighing20kgat4monthsand30kgat 8monthshadsimilarcarcassfatandleanpercentagesto20-kgMerinocarcassesat8monthsandfirst-crossPD ·Mcarcasses weighing30kgat14 months, respectively. At40-kgcarcass weight, 22-month-oldMerinoshad similarlevelsofleannessto carcasses from 22-month-old PD ·M animals and carcasses from 14-month-old second-cross PD ·BLM animals. Carcass leanmeatcontentdecreasedwithincreasingcarcassweightandfirst-crossBL ·Manimalshadthelowestcarcassleanacross allweightcategories.Therewasamajoraccelerationincarcassfatnessbetween14and22monthsassociatedwithareduction inmuscle deposition.Results indicatethatage ofthe animalshouldbe taken intoaccount whencarcass leanand fat contents are compared at a particular carcass weight. Merinos will achieve weight/composition specifications at least equally well to crossbreds but will take longer with a likely increase in production costs.