In the genetic model: Phenotype = Genotype + Environment. Genotype represents the genetic potential of an animal to reach a level of performance and can be split into two components — 1) The component of Breeding Value (additive genetic merit) and 2) Gene Combination Value (GCV), which can also be thought of as the non-additive part.
We use selection decisions to build Breeding Value (BV). Mating decisions influence GCV. Based on your breeding objectives and what traits you consider to be of primary importance to unlocking profit potential in your commercial cow-calf operation, selection and mating are tools in your tool box to build better genotypes.
Heritability can be thought of as the amount of phenotypic variation which is explained by additive genetic variation. As such, heritability serves as an indicator of how easily traits can be changed through selection.
When traits are highly heritable (40% or more), less of phenotypic variation is explained by GCV or environmental influences. On the other hand, low heritability traits are influenced to a greater degree by the GCV part of genotype and the environment.
For example: if the trait of Heifer Pregnancy is estimated to have a heritability of 7%, it follows that 93% of the variation we see in phenotypes for Heifer Pregnancy are influenced by GCV and environment.
The biological phenomenon of heterosis (or hybrid vigor) is the result of GCV from the mating decision to crossbreed. The following table shows the inverse relationship between heritability and heterosis relative to categories of traits.
The table shows that low heritability traits show a higher level of heterosis. High heritability traits are influenced more by additive genetic merit and to a lesser extent due to GCV.
Highly heritable (carcass) traits are most effectively improved through selection programs to improve additive genetic potential. We can impact low heritability traits more quickly through crossbreeding to capitalize on heterosis.
In regard to building back a better cow herd through sound, intentional selection and mating decisions, the single strongest argument for crossbreeding is the advantage in reproductive fitness and longevity of crossbred cows.
If crossbreeding, remember that heterosis does not substitute for additive genetic merit, it builds off of it. Selection of breeds (and breeding stock within those breeds) should be based on EPDs, indicating the BV for traits most economically important in your production system.
Analysis of all the components of your production system including your intended use and marketing endpoint for each calf crop should dictate the selection and mating decisions you make.
Your Next Reads:
Building Back Better Using Selection Decisions and Breeding Values
Building Back Better: Tips for Replacement Heifer Development
Building Back Better Using Breeding Objectives and Selection Pressure
Building Back Better by Analyzing Your System
Building Back Better: Better Genotype Through Selection and Mating
Building Back Better With Mating Decisions and Gene Combination Value
