Economic Weighting of Traits

There are $t$ traits of economical importance to a particular species. Let $\textbf{g}$ be a vector of length $t$ of true breeding values. The Aggregate Genotype, H:

$H=\textbf{v’g}$

Where $\textbf{v}$ is a vector of relative economic values of the $t$ traits in $\textbf{g}$. This can then be approximated by a Selection Index, I:

$I=\mathbf{w'\hat{a}}$

Where $\mathbf{\hat{a}}$ are the EBVs on $m$ traits for one animal and $\mathbf{w}$ are relative economic weights.

​​ Aggregate Genotypes

Contains all the traits of economic importance. Not all information may be known for these traits. Includes all the traits the breeder may want to improve or change and the breeder must define their goals. The Aggregate Genotype is the plan to follow.

​​ Selection Index worked example

​​ Relative Emphasis

​​ Custom Made Indexes

Mating Systems

Which animals of the ones we have selected for mating, should be mated with each other. We should consider:

• the traits to be improved

• the traits to not diminish

• rate of inbreeding

• purpose of mating

• Rate of inbreeding

  • Increases the homozygosity of alleles

• Purpose of mating

  • What reasons are we mating our animals? (protein, fat, milk solids)

• Selection index

  • Mating based on economic importance
    • Would be bad to mate two animals with negative EBV for a given trait

​​ Mating On Index Values

• Random Mating
  • Mating random selected males and females with each other
• Assortative Mating
  • Positive Assortative Mating
    • Index all animals and mate the best with the best and the worst with the worst
    • Creates more variability
  • Negative Assortative Mating
    • Index all animals and mate the best with the worst and vice versa
    • Creates a population closer to the mean

​​ Mating Based on Relationship Status

​​ Linebreeding

• Increasing animals in herd that are related to a particular animal. Inbreeding can take place to concentrate the good alleles in the line.

​​ Deliberate Inbreeding

• Increase homozygosity of alleles at a gene loci
• Inbreeding Depression happens when a performance trait that is influence by non-additive genetic effects - dominance - takes place. Inbreeding can be used to fix this allele, by making the chosen dominant allele homozygous. Guaranteeing offspring to have this trait.

​​ Inbreeding Avoidance

• Outcrossing
  • breeding with the most unrelated breed possible
• Crossbreeding

  • Mating animals of different breeds

  • Heterosis (or Hybrid Vigor) is the superiority of crossbred offspring compared to the average of the two parental breeds

    $H=100*Average of Crossbred - Average of Parents/AverageOfParents$

​​ Crossbreeding Systems

​​ Single Cross

• Rotation System
• Mating between two breeds

​​ Terminal Sire Systems

• Breeds that have good maternal characteristics are mated in a rotation system, and breeds that have good performance traits are mated in another rotation system.
  • Two or more breeds in each system
  • Crossbred females from maternal system then mate with best males from performance system - All offspring go to market (not for breeding)

​​ Composite Breeds

• An animal constructed from two or more breeds. It is created to have the good qualities of each breed in it.