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RESEARCH ARTICLE
Contents Vol 48(7)

Intramuscular fat levels in sheep muscle during growth

M. J. McPhee A B , D. L. Hopkins A C and D. W. Pethick A D E
+ Author Affiliations
- Author Affiliations

A Australian Sheep Industry Cooperative Research Centre, Armidale, NSW 2350, Australia.

B NSW Department of Primary Industries, Beef Industry Centre of Excellence, JSF Barker Building, NSW 2351, Australia.

C NSW Department of Primary Industries, Centre for Sheep Meat Development, Cowra, NSW 2794, Australia.

D Department of Veterinary Biology and Biomedical Science, Murdoch University, South Street, Murdoch, WA 6150, Australia.

E Corresponding author. Email: D.Pethick@murdoch.edu.au

Australian Journal of Experimental Agriculture 48(7) 904-909 https://doi.org/10.1071/EA08046
Submitted: 22 January 2008  Accepted: 21 April 2008   Published: 20 June 2008

Abstract

A 5 × 4 factorial experiment was designed in which lambs representing five genotypes were slaughtered at four ages (110, 236, 412 and 662 days of age). The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorsetgrowth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Both sexes (ewes and wethers) were represented for each genotype and slaughter age combination. In total, 595 animals were slaughtered and the carcass composition and intramuscular fat were measured. Carcass composition [fat, ash and protein (lean)] was determined by dual energy X-ray absorptiometry, with the intramuscular fat percentage determined using near-infrared spectroscopy following removal and weighing of the entire longissimus thoracis et lumborum (LL) muscle. Analysis revealed that the proportion of intramusular fat in the loin relative to total carcass fat decreases as animals mature, thus indicating that intramusular fat deposition occurs early in the maturation of sheep. Furthermore, as animals became heavier and older the accretion rate of intramuscular fat in the LL muscle slowed down. Both genotype (P < 0.05) and sex (P < 0.001) were found to impact on this pattern, with Border Leicester × Merino animals exhibiting the largest increase in intramuscular fat proportion in the LL muscle (4.92 and 5.50% at 22 months of age for ewes and wethers, respectively). The Poll Dorsetgrowth × Border Leicester Merino animals were found to have the greatest absolute levels of intramuscular fat in the whole LL muscle (80.95 and 97.60 g at maturity for ewes and wethers, respectively). The amount of intramuscular fat significantly increased as the sheep became older and fatter; however, these differences were quantitatively small. As such, finishing prime lambs to high levels of total carcass fatness would have little effect on any eating quality benefits associated with increased intramuscular fat proportion.


Acknowledgements

Technical support for this study was provided by David Stanley, Leonie Martin, Edwina Toohey, Tony Markham, Jayce Morgan, Sally Martin, Brent McLeod, Steve Sinclair, Joe Brunner, Stuart McClelland and Amanda Lang (NSW Department of Primary Industries), Kirstie Martin and Kirsty Thomson (formerly University of New England), Peter Allingham (CSIRO) and Tracy Lamb and Rachel McGee funded by CSIRO, Drs Eric Ponnampalam, Danny Suster and Matt McDonagh, Matt Kerr, Dete Hasse, Oliver Fernando, Erin Rutty and Fahri Fahri (DPI, Victoria), Dr Greg Nattrass (SARDI) and Dr Martin Cake and Mal Boyce (Murdoch Uni). Testing of samples for IMF was undertaken by the meat science section at the University of New England. The excellent co-operation of employees and management from Junee and Hillside abattoirs is gratefully acknowledged. The study was funded by NSW Department of Primary Industries, Meat and Livestock Australia and the Australian Sheep Industry Cooperative Centre.


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