A collaborative project has been established in AgResearch and at the University of Adelaide to identify genetic markersfor carcass composition and meat quality traits in beef cattle. Two extreme breeds were used, Jersey (J) and Limousin (L).First-cross Jersey x Limousin bulls (X) were mated to cows of both breeds to produce three-quarter Jersey (XJ) and threequarter Limousin (XL) animals. A total of 261 and 155 back-cross cattle of both sexes were slaughtered as 2-year-olds atRuakura in the springs of 1998 and 1999, respectively. A further 400 cattle of the same back-crosses are under evaluationin Australia. Relative to the mean off-pasture weight and hot carcass weight of the XJ cattle slaughtered at Ruakura in1998 (404 and 202 kg), the corresponding XL means were 472 and 262 kg respectively, 1.8 and 2.6 phenotypic standarddeviations (s.d.) heavier. A series of carcass composition traits was obtained from the weights of saleable meat, trimmedfat and bone from individual joints on the right side of each animal, after 24 h in the chiller. Over all joints, the weights ofmeat, fat and bone (as a % of their total) were 66.6, 9.6 and 23.8 for XJ and 71.7, 7.1 and 21.2 for XL, representingdifferences of 2.8, 1.4 and 2.2 s.d. units respectively. Weights of high value cuts (% of side weight) were 50.4 for XJ and52.7 for XL, a 2.3 s.d. difference. Ratios of meat to bone were 2.80 for XJ and 3.93 for XL, a 5.5 s.d. difference. Standarderrors of all the above differences in s.d. units were 0.16. The largest differences between the two breed crosses for theabove traits were 2.8 and 5.5 s.d, for meat percent in the side, and for meat to bone ratio, providing good opportunities forgenetic marker studies. In the AgResearch animals, consisting of progeny from three sire groups, markers from over halfof the genome have been analysed so far. A significant marker has been identified for meat percent in the side. The twoinformative sires had the same genotype for this marker, and the difference between sire-derived alleles in their effect onmeat percent averaged 0.99 s.d. (F statistic for each sire, 45.47 and 8.84).
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 113-114, 2000
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