Booroola Merino sheep were developed on the Southern
Tablelands of New South Wales, Australia. They differ from normal Merino in two
ways. First, they are more fertile; their fertility is as high as any breed in
the world. The number of lambs born per ewe lambing is 2.4, with a range of 1
to 6. Half-Booroola ewes on average wean 20 percent more lambs than comparable
Merinos under the same conditions. Secondly, Booroolas have the ability to
breed at most times of the year, thus extending the breeding season.
The high profligacy of the Booroola Merino is due to the
action of a single gene. Booroola actually refers to a gene called the B gene
(also called F for fecundity). The B gene can be transferred into any breed
sheep and does not appear to be influenced by nutrition.