As the spring bull selling season gathers momentum across northern NSW and Queensland, many bulls will be valued by commercial producers and graded against a host of requirements.
Ideally, selection decisions are driven by profit-based breeding objectives and the need to make improvements to the genetic makeup of a herd to achieve a production outcome.
The ability to shape selection decisions based on access to performance data has helped manufacturers increase confidence in their overall selections. However, there are some important caveats that should be factored into the decisions that are made.
One of the first is to objectively consider the record of performance being undertaken by a given prefix or seed producer. While many bull breeders will be offering animals this year with EBV, not all producers will have shown a similar degree of rigor in recording and submitting data for analysis.
While recording large amounts of data will result in improvements in accuracy, there is also the potential for producers to record only one or two traits, or even just submit a DNA sample, and still receive EBV for bulls. their sales. The result is a series of EBVs that can be used in a selection decision, however it is important to note that these EBVs based on lower enrollment levels will tend to have lower accuracy.
In practice, the lower accuracy means that there is a greater potential for EBVs to change as more data is collected, and so a bull that may meet a producer’s requirements on first inspection can easily fall through the cracks. out of the spotlight as more is known about him and his genetics.
For producers looking to build a short list of bulls to physically inspect, accuracy assessment can be the difference between buying a bull that is a great fit and one that later turns out to be a marginal choice. An effective way to consider where to start looking for bulls is to look for those breeders who are careful in their registration and who have sires with the highest accuracy, especially for traits that are important to a particular target. breeding.
There are many producers who will shape their selection decisions by reference to the heritability of traits and their correlation with other traits. Understanding what genetic correlations mean is essential in this process.
Perhaps even more important is the reflection of how important these correlations are in a practical sense.
Genetic correlations
Genetic correlations describe how two traits, on average, tend to vary (or not) in common. This is expressed as a number between -1 and +1. Traits with a negative correlation describe cases where, as one trait increases, there is a corresponding decrease in the other, while positive correlations describe a common increase (or decrease) for both traits.
Correlations closer to the absolute value of -1 or +1 describe cases where a change in one trait is strongly associated with a change in another, while lower numbers (closer to 0) essentially mean that for those pair of traits there will be no the pattern of how one changes in relation to the other.
Dr. Matt Wolcott from the Animal Genetics and Breeding Unit in Armidale provided an overview of genetic correlations as part of a contribution to the recently published ‘Top Studs – 2024’ report by Bush Agribusiness.
Dr. Matt Wolcott
“Genetic correlations are assessed as part of the development that supports BreedPlan and are one of the key components of its multi-trait assessment,” said Dr Wolcott.
At the analytical level, genetic correlations help maximize the information obtained from the census that seed breeders make.
Dr Wolcott notes that “for producers trying to make selection decisions in yards, trying to account for trait correlation is not only extremely complex, it is largely unnecessary.”
As part of Matt Wolcott’s contribution to Top Studs, he summarized the average heritabilities and genetic correlations between traits in BreedPlan’s ratings for soft-meat breeds.
The figure below shows that genetic correlations tend to be moderate to weak, with the only strong relationships seen between some weight traits, or two measures of fat depth (Rib and P8).
Average heritability (on the diagonal) and genetic correlations between trait pairs in BreedPlan estimates for soft meat breeds – Dr Matt Wolcott AGBU; Source: Bush Agribusiness, Top Studs 2024. Click on the chart for a larger view.
What this means in practice is that while carcass weight, for example, is moderately heritable (meaning there is potential for improvement through selection), the genetic correlation with other aspects of carcass composition (fatness of ribs and P8, eye muscle area, retail beef yield and marbling) are moderate at best and not all in the same direction.
Dr Wolcott explains this statement, “In this example, there are only moderate to weak genetic correlations of carcass weight with other aspects of carcass composition, and both negative and positive correlations can be observed between carcass traits in the BreedPlan evaluation for soft meat breeds.
“Therefore, relying on EBV with carcass weight to provide useful information about a bull’s genetics for other aspects of carcass composition will be ineffective, at best.”
Critically, genetic correlations describe what is observed on average, and they make the greatest contribution to the estimation of breeding value where data on correlated traits are scarce or absent.
In cases where all traits in the breeding target are recorded and included in the evaluation, the impact of genetic correlations on breeding value estimates becomes negligible.
Matt Wolcott’s advice to producers is to recognize that “accurately recording correlated traits will always exceed expectations of how traits vary in common, at the genetic level, described by their genetic correlates.”
This means that a key question in assessing the suitability of the stud as a source of bulls for your herd is – Do they record the traits that are important to my breeding objectives?”
Alastair Rayner is General Manager of Expansion and Operations with Cibo Labs and Director of RaynerAg. Alastair has over 28 years of experience advising beef producers and carriers throughout Australia. He can be contacted here or through his website www.raynerag.com.au