Selection of cattle is the process by which we determine which animals become parents, how many offspring they will produce and how long they will remain in our breeding herd. When we select replacement heifers or herd bulls we are practicing selection. When we cull old, open cows or ornery herd bulls we are practicing selection. The focus of this article is on replacement selection. Specifically, the best way to determine which animals will become the parent stock in our commercial cow-calf operation.
After we have analyzed our production system, identified our breeding objectives and determined the traits on which to apply selection pressure, the goal is to identify the animals with the best genes and let them reproduce. The animals with the best genes are said to have the best Breeding Value (BV). BV, based on the additive genetic effect of individual genes (across the genome), serves as the best indicator of an animals genetic value as a parent. BVs are trait specific. Since BVs are based on the effects of individual genes, they represent the part of genotype which can be passed from parent to offspring. Successful selection is based on identifying the animals with the best BVs (for traits of primary economic importance) to become our next generation of parents. Using Expected Progeny Differences (EPDs) in sire selection or Genetic Merit Scorecards on groups of commercial heifers are examples of modern tools available to assist us in determining the BV of potential parent stock in cow-calf operations.
Heritability is important to define relative to selection. Heritability is the relationship between phenotypic values and breeding values for a trait in a population. More precisely, heritability is the proportion of phenotypic variation that can be explained by additive genetic variation for a given trait. Quantitative, polygenic traits in beef production can be lumped into three categories. These include: Reproductive traits (for example: heifer pregnancy percentage or rebreeding intervals in the cow herd). Reproductive traits are low in heritability. Scientific literature indicates the heritabilities of reproductive traits fall into a range between 0 to 20%. Growth Traits (for example: weaning weights or yearling weights), are moderate in heritability typically falling into a range between 20 to 40%. Carcass traits (such as marbling, fat thickness or ribeye size) are highly heritable (40% or higher).
For example, the Sire Summary of the American Angus Association currently estimates the heritability of carcass marbling to be 48%. This can be interpreted to mean that the additive genetic variation of marbling accounts for 48% of all the variation we observe in marbling phenotypes.
In summary, selection should be based on identifying animals with the best BV for traits of primary economic importance. Effective selection decisions lead to building additive genetic potential. Additive genetic change is cumulative and permanent. While genotypic value represents the overall effect on an individual animal’s genes, BV represents the only part of genotypic value that can be transmitted from parent to offspring. Finally, heritability estimates for a given trait serve as an index of how easily the trait can be changed through selection.
The other part of genotype is Gene Combination Value (GCV). Since it is the result of genes paired at loci across the genome, and only one gene from each locus is transmitted by parents, it represents the part of genotype which can’t be passed from parents to offspring. GCV will be discussed in more detail next week.
Dr. Mark Johnson, OSU Extension beef cattle breeding specialist, continues his Build Back Better series with an in-depth look at genotypes, selection, and mating. Learn how genetic selection and mating strategies can strengthen your herd’s long-term performance and profitability on SunUpTV from Dec 6, 2025. https://www.youtube.com/watch?v=bsGVAySqtfE
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