Genetic variations in body composition are apparent as differences among breeds, crosses, selected strains and sire groups. Crossbreeding, use of terminal sires and selection within breeds has tended to concentrate on total meat output rather than quality, despite consistent consumer signals against fat. Evidence suggests that, in males selected using live animal ultrasound measurements of fat and muscle depths, about half of the selection pressure available to improve growth rate should be sacrificed in order to maximise economic response through decrease in carcass fat content. Genetic variations in lean/fat partitioning to different regions and muscles of the carcass, and in traits affecting the wider sensory appeal of cooked meat, are also important to the range and consistency of meat products. Indirect live animal indicators are vital to minimising the high cost of progeny testing. Meat product tenderness is one example. Much of the variation is under the control of the calpain system for which genetic differences have been found among breeds and crosses, related families, selection lines, and in strains segregating for major genes and genetic markers (e.g. calpastatin and the CSSM18 and TGLA122 markers of the callipyge gene in sheep). Decreased post mortem tenderness is associated with decreased proteolytic enzyme activity which in some cases is related to increased lean growth rates in the live animals as well. Between and within muscle variations in actin/myosin interactions, lipid, myoglobin contents and solubilities can also give rise to genetic variations in tenderness, meat flavour, colour and the heat gellation properties of myosin. The biochemical basis of these effects suggests useful indicator traits (e.g. LDH and ICDH enzyme activity associations with fibre type, intra-muscular fat and haem iron contents) which are likely to offer innovative genetic solutions to long-term industry competitiveness.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 157-162, 1996
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