animal breeding Elements needed to make genetic progress

Genetic gain per year (ΔG) depends on balancing several factors, as expressed in the equation ΔG=(Aσ_gi)/I,where A is the accuracy of selection, σ_g is the standard deviation of the additive genetic variation in the population, i is the selection intensity (proportion selected for further breeding), and I is the generation interval (age of breeding). The σ_g factor cannot be easily changed within a breed, though it can be changed by crossbreeding. The other quantities in the equation can be changed. More complete pedigree records on candidates for breeding can increase the accuracy of selection, but waiting for candidates to reach full maturity in order to have better genetic data will increase the generation interval. Whether an increase in generation interval is justified by a more accurate selection process depends on individual circumstances. Selection intensity can also be increased, by narrowing the proportion of the population used in breeding, but it should be done without increasing the generation interval. Because generation interval is the divisor in the genetic gain equation, anything that increases the generation interval has an unfavourable impact on genetic progress, all else being equal.