Genotype and age effects on sheep meat production 4. Carcass composition predicted by dual energy X-ray absorptiometry
E. N. Ponnampalam A B G , D. L. Hopkins C , F. R. Dunshea B F , D. W. Pethick E , K. L. Butler D and R. D. Warner BA Australian Sheep Industry Cooperative Research Centre, Armidale, NSW 2350, Australia.
B Animal Production Sciences Platform, Department of Primary Industries, 600 Sneydes Road, Werribee, Vic. 3030, Australia.
C NSW Department of Primary Industries, Centre for Sheep Meat Development, PO Box 129, Cowra, NSW 2794, Australia.
D Science Innovation and Quality, Department of Primary Industries, 600 Sneydes Road, Werribee, Vic. 3030, Australia.
E School of Veterinary and Biomedical Science, Murdoch University, Murdoch, WA 6150, Australia.
F Present address: The University of Melbourne, Melbourne, Vic. 3010, Australia.
G Corresponding author. Email: eric.ponnampalam@dpi.vic.gov.au
Australian Journal of Experimental Agriculture 47(10) 1172-1179 https://doi.org/10.1071/EA07008
Submitted: 9 January 2007 Accepted: 28 March 2007 Published: 19 September 2007
Abstract
This study compares the carcass composition of different genotypes of Australian sheep slaughtered at four ages (110, 236, 412 and 662 days of age, or 4, 8, 14 and 22 months of age). The genotypes used were Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M). Approximately 150 mixed sex animals were slaughtered at each age and the right sides (half carcass) were scanned by dual energy X-ray absorptiometry (DXA) for chemical lean, fat and bone mineral percentages of the carcass. Carcass lean percentage decreased (P < 0.001) across sire groups from Merino to Poll Dorset to Border Leicester at each age, while fatness increased (P < 0.001) in the opposite direction. With age, the magnitude of difference between genotypes for fatness became greater. There was a marked increase (P < 0.01) in ash mineral percentages in M × M and PDg × M genotypes relative to other genotypes in the 14- and 22-month groups. There were no differences (P > 0.1) between PDg × M and PDm × M in either chemical lean or fat percentages at any age but ash mineral percentage was higher in the PDg × M genotype at older ages (P < 0.05). This in turn led to differences in chemical lean : ash mineral content at later ages between PDg × M and PDm × M. Wethers had higher chemical lean (P < 0.05) and lower fat (P < 0.05) percentages in the carcass than ewes at all ages but ash mineral and chemical lean : ash mineral content did not differ between sexes. It was clear that the level of chemical lean or fat or ash mineral composition reached by some genotypes at one age was equivalent to that reached by other genotypes at the next measurement age. Those genotypes that reach a specification at younger ages will be more productive for meat production. Purebred Merino genetics will always be less productive in terms of carcass weight and muscle related productive traits (loin weight, semitendinosus muscle weight, eye muscle area) than BL and PD genetics, but the relative productivity of PD and BL genetics will depend on the traits used in the specification [see also Ponnampalam EN, Hopkins DL, Butler KL, Dunshea FR, Warner RD (2007) Genotype and age effects on sheep meat production. 2. Carcass quality traits. Australian Journal of Experimental Agriculure 47, 1147–1154]. The results suggest that selection for muscling had a greater impact on reducing ash mineral content associated with bone mineral mass than on increasing lean mass in the carcass.
Acknowledgements
Technical support for this study was provided by Tony Markham, Jayce Morgan, Andrew Roberts, Sally Martin, Brent McLeod, Steve Sinclair, Joe Brunner, Stuart McClelland and Amanda Lang (NSW Department of Primary Industries), Kirstie Martin and Kirsty Thomson (University of New England), Peter Allingham (CSIRO), Tracy Lamb and Rachel McGee were funded by CSIRO, Drs Danny Suster and Matt McDonagh, Matt Kerr, Dete Hasse, Oliver Fernando, Erin Rutty, Paul Eason and Fahri Fahri (DPI, Victoria), Dr Greg Nattrass (SARDI) and Dr Martin Cake and Mal Boyce (Murdoch University). The excellent co-operation of Junee Abattoir employees and management is gratefully acknowledged. The study was funded by Meat and Livestock Australia and the Australian Sheep Industry Cooperative Centre.
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