AGB 211: Livestock and Poultry Breeding (2+1)

RECIPROCAL RECURRENT SELECTION

• It is a system of selection for increasing the combining ability of two or more lines or breeds that nick or combine well. Individuals in two lines are not completely homozygous in opposite ways for all pairs of genes but that one allele may be present at a high frequency in one line and at a low frequency in other line. Crossing the lines and selecting the individual to reproduce each pure line on the basis of the performance of their crossbred progeny make the two lines more homozygous in opposite direction. It is a method of selection between lines or families or breeds to take advantages of overdominance, dominance, epistasis, or only additive effects.
• In farm animals, selection is usually carried out for more than one trait, since one trait may be affected mostly by non-additive gene action and another by additive gene action or both. Hence, it is to select and improve the best and mating the best to best followed by crossing the improved lines or breeds to take the advantage of hybrid vigour due to non-additive gene action.
• Randomly selected representatives of each of the non-inbred strains are progeny tested in crosses with the other. Those individuals of each strain having the best cross progeny are then intermated to propagate their respective strains. Offspring from these within strain mating are again progeny tested in crosses with the other and the cycle repeated.

• These systems are useful in breeds or strains in which their performance is already high for highly heritable traits and in which it is desired to improve the potential performance of their crosses for the low heritable traits related to fertility and liveability e.g. litter size and early growth rate in swine.