Growth and carcass characteristics of Dorset down sired lambs from six ewe genotypes : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours) at Lincoln University

In New Zealand a large part of the national export earnings comes from sheep farming (Morris and Clarke 1982), with a high proportion of these earnings derived from lamb production. World markets, as for other meats, are increasingly rejecting fatness and waste (Fraser, Stamp and Cunningham 1987). This has continued to put pressure on the processing industry which in turn imposes serious financial penalties on over fat lambs (Bray, Moss, Barton and Saville 1990). Premiums are also paid for heavy lambs, with some of the savings associated with lower per kilogram processing costs being passed down to the lamb producers. Therefore, within a given time frame, the carcass that produces the greatest income is heavy with a low GR measurement. Lambs achieving this target at younger ages will typically return greater profits to the farmer. Unfortunately carcass weight and fat traits have a positive correlation where high carcass weights tend to have a high fat measurement (Waldon, Clarke and Rae 1991). One of the difficulties farmers face, is producing carcasses that are lean enough at the desired weight. This paper, therefore, aims to identify the determinants of growth and carcass characteristics, emphasising those which lead to production of heavy, lean lambs within a time short period. A model has been proposed identifying the key components, as distinguished by this trial, which determine the efficiency of lamb production relative to current weight and fatness demands