LIMITS TO SELECTION

Press, Volume CIX, Issue 32050, 26 July 1969, Page 8

LIMITS TO SELECTION

“Selection of prolific strains can increase the lamb crop but within a breed it is generally considered that there is a genetic limit and the nearer the limit in selection the more difficult it is to make further progress,” Mr T. W. W. Jones, an English district advisory officer now in New Zealand under an exchange .scheme, told farmers at the North Canterbury conference at Waipara last week.

“Cross-breeding may, therefore, be a short-cut to increased lamb crops,” he said. Mr Jones said about 30 per cent of the ewe flock in the United Kingdom were cross-

breds derived mainly from longwool rams crossed with mountain ewes. There was a three-tier system where hill breeds were bred pure in the hill country, with older ewes being brought on to lower ground or drafted off the hill farm to the foothills for crossing with longwool rams to produce crossbreds, which on lowland farms were crossed with Down rams to produce the fat lamb. The best known examples of this system were the Scotch Blackface ewe crossed with the Border or Hexham Leicester to give the Mule dr Greyface, the North County Cheviot crossed with the Border Leicester to give the Scotch Halfbred and the Swaledale ewe crossed with the Teeswater ram to produce the Masham. All these cross-

breeds were capable of lambing percentages of up to 200 per cent, though 150 per cent would be the average, and they made exceedingly good mothers.

“That improved prolificacy can be obtained by crossbreeding has been shown by the Coopworth and the Perendale,” said Mr Jones. “This is- much quicker than by selection within existing flocks of the desired type. “Recording, selection, and breeding whether within a pure breed or with crosses is a slow process and large numbers of animals are required. In New Zealand Romney breeders’, groups have outlined programmes whereby breeders are pooling resources to select elite ewes and rams of improved prolificacy. This will certainly improve the lambing percentage, but eventually a stage will be reached when the genetic potential of the breed will have been achieved and the introduction of new genes

will be necessary to obtain further increased prolificacy. “By cross-breeding and rigorous selection it is easier to combine together desired characteristics. Basic information on the pure breed and large numbers'will be required. It is, however, by no means a static situation and what is required toddy may not be in the future and new breeds with different combinations of genetic material will be continually evolved.”