Non-random mating for selection with restricted rates of inbreeding and overlapping generations.

Anna K Sonesson,Theo H.E Meuwissen

doi:10.1186/1297-9686-34-1-23

Abstract

Minimum coancestry mating with a maximum of one offspring per mating pair (MC1) is compared with random mating schemes for populations with overlapping generations. Optimum contribution selection is used, whereby ΔF is restricted. For schemes with ΔF restricted to 0.25% per year, 256 animals born per year and heritability of 0.25, genetic gain increased with 18% compared with random mating. The effect of MC1 on genetic gain decreased for larger schemes and schemes with a less stringent restriction on inbreeding. Breeding schemes hardly changed when omitting the iteration on the generation interval to find an optimum distribution of parents over age-classes, which saves computer time, but inbreeding and genetic merit fluctuated more before the schemes had reached a steady-state. When bulls were progeny tested, these progeny tested bulls were selected instead of the young bulls, which led to increased generation intervals, increased selection intensity of bulls and increased genetic gain (35% compared to a scheme without progeny testing for random mating). The effect of MC1 decreased for schemes with progeny testing. MC1 mating increased genetic gain from 11–18% for overlapping and 1–4% for discrete generations, when comparing schemes with similar genetic gain and size.

Highlights

For breeding schemes, the selection step determines the increase in average coancestry of the population, but the mating step can improve the genetic structure of the population for the round of selection
When using optimum contribution with a restriction on ∆F and discrete generations, minimum coancestry mating with only one progeny per mating pair (MC1) increased genetic response from 5 through 23% compared with random mating
Because MC1 mating makes relationships more homogenous across families, the relationship among animals with the highest Estimates of breeding values (EBVs) will be reduced. It will be easier for optimum contribution selection to select animals with the highest EBVs when MC1 mating is used instead of random mating

Summary

Introduction

The selection step determines the increase in average coancestry of the population, but the mating step can improve the genetic structure of the population for the round of selection. When using optimum contribution with a restriction on ∆F and discrete generations, minimum coancestry mating with only one progeny per mating pair (MC1) increased genetic response from 5 through 23% compared with random mating. Factorial mating schemes [17] avoid extreme relationships by exchanging full-sib relationships for (maternal) half-sib relationships, which is done in the MC1 scheme by restricting the number of progeny per mating pair to zero or one Both these effects result in a population with more homogenous relationships among animals. A third effect of non-random mating, especially minimum coancestry mating, are decreased inbreeding levels of the progeny and of parents of the generation, which leads to a larger Mendelian sampling variance. A larger Mendelian sampling variance leads to increased genetic variance and genetic gain

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