Factors influencing the rate of genetic improvement
The rate of genetic improvement in a beef herd is influenced by multiple factors. These include selection intensity, accuracy of selection, genetic variation, and generation length.
Selection intensity is the difference between the genetic value of animals selected as parents and all animals available for selection. A higher selection intensity drives a higher rate of genetic improvement. Typically, higher selection intensity is applied to males (only a small percentage of all male calves are used as sires) than to heifers (a large percentage of all female calves are retained as dams).
More genetic gains will be achieved if selecting the top 5% of available animals as parents than if selecting the top 50%. For females, culling the bottom 50% of potential replacement heifers versus the bottom 10% would increase your selection intensity and drive genetic gain.
Accuracy of Selection
This refers to how accurately you select breeding animals. More accurate selection drives the rate of genetic improvement.
Accuracy of selection can be improved by making use of all available information. To improve your selection accuracy:
- Source your bulls from a seedstock producer that records all traits that are of interest to you
- Use genetic tools such as BREEDPLAN to better understand the genetic merit of an animal (this will be explored in more detail in Module 2: Breeding objectives – COMING SOON)
- Using DNA technologies (where available; see Module 6: DNA Technologies in beef breeding – COMING SOON for more detail)
Greater genetic variation provides a greater potential to make genetic improvement.
Access to a wider range of genetic variation can be achieved by sourcing genetics from a range of bull breeders. This may include bulls from another breed (e.g. crossbreeding) and/or semen from bulls for use in AI programs.
Generation length is the average age of the parents in a population at the time that their progeny are born. A shorter generation length drives the rate of genetic improvement by bringing younger, genetically superior replacements into the breeding herd.
Some ways in which you can reduce the generation length in your herd include:
- Lowering the age of your heifers at first calving (e.g. from 3 year old to 2 year old)
- Retaining a higher proportion of replacement heifers
- Using yearling bulls
- Culling animals based on genetic merit rather than age
It is important to be aware of the antagonistic relationships between some of the factors that influence the rate of genetic improvement in a herd. For example, using yearling bulls to lower generation length may also lower the accuracy of selection (as generally yearling bulls have less information recorded than older bulls).
Specific characteristics in animals can be achieved through selectively breeding parents, so that progeny are produced with the more desirable characteristics.