Alternative selection strategies for the Mutton Merino breed to optimize breeding systems

This paper deals with the investigation of alternative selection strategies for the Mutton Merino breed to improve lamb meat production and fertility. A main topic is the application of ultrasonic scanning to evaluate the mea t content on live animals. The aim of model calculations was the optimisati on and comparison of five different selection strategies within three diffe rent schemes of gene dissimation. First a basic scheme was defined and opti mised (selection on field records, one-step selection, no scanning). It was regarded as the reference scheme to which all other breeding systems were related. The following schemes considered both, selection with and without scanning. A second scheme, also based on field records, includes two-step s election of rams (called improved field test scheme). In a third and fourth scheme a level of uniform environment was assumed for ram progeny testing. These are a central testing station on the one hand with slaughtering and carcass evaluation on progeny, and one or more contract farms on the other (without slaughtering). For a fifth selection scheme an open nucleus was as sumed with ram progeny testing in associated test herds. In a deterministic approach using the ZPLAN computer program, the monetary genetic gain for the breeding objective (traits lambs weaned, litter weight at weaning, postweaning daily gain and lean meat content) and the profit w ere calculated for each scheme after optimisation of various biological-tec hnical coefficients. The highest profit was achieved with a nucleus scheme (DM 9,16). Due to low recording costs the basic scheme was second (DM 7,19) and, because of high costs, the station scheme was last (DM 4,22). The oth er two schemes were intermediate (DM 6,98 for the scheme with contract farm s and DM 6,58 for the improved field test scheme). On an average over all s chemes, scanning resulted in a 0,24 DM (i.e. almost 30 per cent) increase o f the monetary genetic gain and a threefold higher genetic gain for lean me at percentage. In all schemes scanning lead also to a higher profit because the higher return of selection based on scanning exceeded the higher costs .