Pure-bred or Composite? - How 'pure' is a pure breed?
Pure 'British Breeds' were historically the 'status' alternative to Merinos. 'Cross-breds' were
second class, usually destined for slaughter. 'Composites' is a newer term, usually for breeding stock with genes chosen for excellence from several breeds.
Studs, the breed societies and ASSBA (Australian Stud Sheep Breeders Association) were historically focussed on keeping established breeds pure. A 'composite stud'
seemed a contradiction in terms! However some stud breeders, as well as their customers, now want to share the new genetic improvement options for both gene selection
and gene transfer. They argue that 'rare breed' enthusiasts can focus on purity, but studs should meet commercial needs. This can be quite controversial.
A complication for many breed societies comes from the new genes involved with breeding to poll. Some breed societies have rules which base 'purity' on the number of
back-crosses to the base breed ancestor, using the logic that after four or five back- crosses the resulting lamb has a very high percentage of the 'blood' of the base breed.
However flocks can go through back-crosses following 'purity' rules, but can still keep more genes than just poll. If the polled ancestor was an old-style 'coat-hanger'
Merino ("just a bone frame for a wool coat"), a buyer hopes that the poor meat genes have been bred out. If the polled ancestor was a White Suffolk, Poll Dorset, Texel or
SAMM, the breeder will probably want to keep its good meat genes as well as the poll gene. If other genes are not bred out, the final flock is more than just a polled
version of the original breed. When a new ram is bought from another flock which has used a different breed as the polled ancestor, complex genetic mixing is inevitable.
Some genes can be checked visually (eg horn genes in rams), and there are genetic tests for some genes (also horn/ poll). However there are no affordable tests to check for
all the genes of other breeds. Even if the 'purity' rules have been followed, you are still buying a combination of breed genes. Whether 'pure breds', 'cross-breds' or
'composites', almost all sheep in Australia have some genetic mixing.
In the future, affordable genetic tests may let every breeder check their flock's genes against a 'pure' standard. There are already hints that the results may be a shock,
and may provide pure breed societies and their members with a lot of problems. Certainly it will put the spotlight on 'purity' as a goal, compared with gene transfer.
In the meantime, both farmers and stud breeders need to make their own decisions!