Hybrid vigor, known as heterosis, describes the superiority in performance of crossbred animals compared to their parents. Crossbreeding, in which males and females of different breeds or breed types mate, is the recommended breeding strategy for commercial sheep production.
Unlike cattle, almost all goat and sheep breeds started out as crossbreeds. Selectively crossbred sheep invariably benefit from hybrid vigor and the tactic can be used for specific purposes depending on the producers' needs. For example, a crossbreeding program intended for slaughter meat uses a male of superior growth and carcass merit, such as a Suffolk or Boer, to produce lambs for the slaughter market while maintaining moderate sized females that excel in fitness and reproductive performance. Another crossbreeding scheme could be aimed at producing crossbred females of a specific type, like Spanish mixed with Kiko or Dorset mixed with Finn, for superior breeding.
Sheep are part of Australian heritage, with 76.9 million at the last count in 2009, and the country is the largest wool exporter in the world. Sheep numbers exploded over the last two centuries, and although some of this growth was due to the active support of Britain in its desire for wool, Australia owed much to selective crossbreeding. The country developed new high-production breeds benefiting from hybrid vigor that are now household names; the Corriedale, Coolalee, Polwarth, Booroola Merino, Peppin Merino, and Poll Merino were all created in Australia.
Australian crossbreds are deliberately well suited to the conditions of the country. For instance the Dorper sheep, which was developed in South Africa in the 1930s by crossing Blackhead Persian ewes with a Dorset Horn ram, is now a hardy, fertile, fast-growing meat breed well adapted to the Australia's climate and geography. It was introduced into Australia in 1996 with the potential to be developed for domestic and export meat markets.
Meanwhile the White Suffolk was specifically developed from breeding programs involving the Suffolk breed crossed with a white breed, mainly Poll Dorsets. Noted for their high quality, white, Downs-type wool, according to the Australian White Suffolk Association it is "an Australian breed developed for Australian conditions." Its parent, The Poll Dorset, is the largest prime lamb sire breed in Australia for slaughter - supplying over 70 percent of sires required annually by the industry.