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Effects of available nutrition and sire breeding values for growth and muscling on the development of crossbred lambs. 1: Growth and carcass characteristics

R. S. Hegarty A G , C. Shands B , R. Marchant C , D. L. Hopkins D , A. J. Ball E and S. Harden F

A Beef Industry Centre of Excellence, NSW Department of Primary Industries, Armidale, NSW 2351, Australia.

B NSW Department of Primary Industries, Glen Innes ARAS, Glen Innes, NSW 2370, Australia.

C NSW Department of Primary Industries, Armidale, NSW 2350, Australia.

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

E Meat and Livestock Australia, Armidale, NSW 2351, Australia.

F NSW Department of Primary Industries, Tamworth Agricultural Institute, Tamworth, NSW 2340, Australia.

G Corresponding author. Email:

Australian Journal of Agricultural Research 57(6) 593-603
Submitted: 12 November 2004  Accepted: 18 June 2005   Published: 20 June 2006


The growth and development of 387 crossbred lamb progeny from 9 Poll Dorset sires representing muscle (M), control (C), and growth (G) sire-types was studied. Sires were selected on the basis of their LAMBPLAN estimated breeding values (EBVs) for post-weaning growth (PWWT) and depth of loin muscle (PEMD). Lambs were provided with either LOW or HIGH levels of available grazing nutrition from 10 days of age onwards. Liveweight gain (LWG) throughout the study was less on LOW nutrition than on HIGH nutrition, leading to a 9.5 kg lower weaning liveweight (LW) and a 14.9 kg lower final LW in LOW lambs. After adjustment for final LW, HIGH lambs had significantly greater fat depth at the C-site (approximately 40 mm from the midline over the 12th rib) and tissue depth at the GR site (110 mm from the midline over the 12th rib) than did LOW lambs. This effect was consistent across sire-types. Depth of fat at the C-site was positively associated with the EBV of the sire for fat depth. The improvement in pre-weaning LWG, weaning weight, and final weight of lambs resulting from use of sires with a greater PWWT EBV was dependent upon the level of nutrition. This interaction was identified as different slopes (coefficients) for the regression between PWWT and trait for the 2 nutrition levels, indicating that the expression of the sire’s genetic potential for growth at these times was significantly moderated by nutrition. The additional depth of lamb loin muscle resulting from use of sires of higher PEMD EBV was consistent across both LOW and HIGH nutrition treatments, with 1 mm of PEMD leading to a 0.6-mm increase in loin depth. Other consequences of sires having a high genetic capacity for loin muscle depth were reduced carcass C-fat depth with increasing sire PEMD and a tendency for conformation score to improve with the PEMD of the sire. The wool-growth response to improved nutrition was less in M lambs than in lambs of other sire-types, suggesting a difference in priority for protein partitioning between muscle and wool in lambs differing in genetic propensity for muscle growth.

Additional keywords: lamb, sheep, genetics, nutrition, carcass, muscling.


Semen from all sires used in this study was provided free of charge by the studs and this contribution is acknowledged with thanks. Technical support for this study was provided by Stuart McClelland, Reg Woodgate, Bill, Johns, Steve Sinclair, David Stanley, and Joe Brunner (NSW Department of Primary Industries). Thanks to Clare Edwards (NSW Department of Primary Industries) for assistance in pasture species identification and classification and thanks to Dr R. Banks, Dr R. Woolaston, and Dr A. Gilmour for assistance in preparation of the manuscript. The study was funded by NSW Department of Primary Industries and Meat and Livestock Australia under the Management Solutions Program.


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