New sheep may be alternative breeds brought in from other environments, new synthetic breeds developed by crossbreeding or as specific crossbred combinations, or new strains of existing breeding populations developed by selection for production traits, identifiable genes or gene complexes. Changing gene frequency is the main underlying feature of all these approaches to genetic improvement. Selection of parents is the common operational ingredient. New products have been a major factor in changing the breed structure of our sheep industry. New more productive breeds have also been produced utilising the complementary features of existing breeds, but with little widespread development of crossbreeding systems based on first cross ewes. Improved reproductive rate from selection or use of new fecund genotypes offers much scope for specialised production of quality market lambs, especially when stratified production a major stimulus to the improvement of terminal sire breeds. They are re-focusing the balance of emphasis on lamb growth and carcass and encourage a search for unique genetic effects on meat quality traits.
Proceedings of the New Zealand Society of Animal Production, Volume 55, , 318-320, 1995
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