Economic benefits in selection for weight and composition of lamb cuts predicted by computer tomography T. Kvame a, * , J.C. McEwan b , P.R. Amer c , N.B. Jopson c a Department of Animal and Aquacultural Sciences, Agricultural University of Norway, P.O. Box 5025, N-1432 Aas, Norway b AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand c Abacus Biotech Limited, P.O. Box 5585, Dunedin, New Zealand Received 29 July 2003; received in revised form 29 January 2004; accepted 15 March 2004 Abstract Consumer preferences for lamb cuts are affected by the size, shape and fatness of cuts. Using computer tomography (CT), the best anatomical scan sites for prediction of weight and composition of four primal cuts; hindleg (HL), loin (LN), rack (RK) and forequarter (FQ) were examined. The economic benefit of incorporating cut distribution into a breeding programme was evaluated. The weight and composition of cuts were predicted by CT in 300 lambs. Each CT image was classified according to anatomical location relative to the spine, and the areas of subcutaneous fat, intermuscular fat, lean and bone measured for each cut. A stepwise regression procedure was used to find the best subset of two anatomical positions to predict the tissue depot weights and total cut weight for each cut. The results show that the weight and composition of primal lamb cuts can be very accurately predicted from six to eight CT scan sites recorded per animal (R 2 range from 0.85 to 0.98 for total cut weights). Net benefit predicted from two selection indices for a hypothetical breeding programme given a 10-year horizon showed higher (NZ$1.02 million) net benefits when selection was for composition of cuts and fat (six images) than breeding for weight of lean and against fat in the carcass (four images). D 2004 Elsevier B.V. All rights reserved. Keywords: Sheep; Computer tomography; Body composition; Carcass value 1. Introduction Internationally, consumer preferences for lamb cuts are affected by the size of cuts and their fatness (Jeremiah et al., 1993). The New Zealand lamb market is largely (91%) for exports of which 53% are sold to the European Union (EU; Meat and Wool Innovation, 2002). In 1995, 75% of the exports to EU were in the form of cuts, compared to only 20% in 1981 (Burtt and Francis, 1996). Ultrasonic scanning of the loin (12th rib) is widely used in commercial breeding programmes as it meas- ures response to selection for composition of lean and fat in the carcass (Afonso and Thompson, 1996; Cameron and Bracken, 1992; Fennessy et al., 1993; 0301-6226/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2004.03.002 * Corresponding author. Agricultural University of Norway, Department of Animal and Aquacultural Sciences, PO Box 5025, N- 1432 Aas, Norway. Tel.: +47-64-94-70-41; fax: +47-64-94-79-60. E-mail address: turi.kvame@iha.nlh.no (T. Kvame). www.elsevier.com/locate/livprodsci Livestock Production Science 90 (2004) 123 – 133