Abstract
A simple and effective procedure based on a combination of weight of greasy fleece shorn and weight of lambs weaned was used to select replacement animals during the development of the Minnesota breeds of sheep in the United States. Ewe productivity based on weighting factors representing conversions of weight of grease fleece shorn for each ewe in terms of weight of their weaned lambs could be typical of those derived from considering costs and returns. This procedure can also be utilised in various countries when attempting to evaluate breeds and their crosses. The Minnesota breeds of sheep represented by 421 ewes and their 367 lambs, and Minnesota breed crosses consisting of 1037 ewes and their 849 Suffolk-sired lambs studied here failed to demonstrate large difference in the performance traits representing two major sources of income from sheep production used to estimate ewe productivity. The ranking among breeds remained fairly consistent when the added value for grease fleece weight increased by up to five folds. The exception was purebred Minnesota 105 demonstrating significantly lower productivity and the crossbred Minnesota 103×107 demonstrating significantly higher productivity. It was concluded that difference in the relative value of weight of grease fleece shorn to weight of lambs at weaning need to be of considerable magnitude for the productivity of breeds to vary dramatically. The use of a combination of weight of grease fleece for the ewe and weight of their lambs at weaning to establish productivity demonstrates promise for the evaluation of breeds, particularly for countries in the vicinity of the Himalayan range where the value of fleece has been increasing from the sale of speciality products. Productivity indices are only recommended for countries and regions within a country, where the application of multi-trait animal model procedures for the simultaneous genetic evaluation of morphological characteristics and production performance for parents and their offsprings is currently not feasible.
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