As the spring bull selling season gathers momentum across northern NSW and into Queensland, many bulls will be assessed by commercial producers and evaluated on a myriad of requirements.
Ideally, selection decisions are made on the basis of profit-based breeding objectives and the need to make improvements in the genetic makeup of the herd to achieve a productive outcome.
The opportunity to base selection decisions on access to performance records has helped producers increase their confidence in their overall choices. However, there are some important caveats that should be included in the decisions that are made.
One of the first things to consider is the performance of a particular seed or seed producer. While many bull breeders will show this year’s animals with EBV values, not all producers will be as meticulous in recording and submitting the data for analysis.
While recording large amounts of data can lead to improvements in accuracy, there is also the potential for farmers to record just one or two traits, or even just provide a DNA sample and obtain EBV values for their bulls for sale. The result is a series of EBV values that can be used in selection decisions, however it is important to note that these EBV values based on lower levels of recording tend to be less accurate.
In practice, the lower accuracy means that there is greater potential for EBV values to change as more data is collected, so a bull that may meet the producer’s requirements at first consideration may easily fall out of consideration as more is known about him and his genetics.
For producers looking to create a shortlist of bulls to physically examine, estimating accuracy can be the difference between purchasing a bull that is a great fit and one that later proves to be a marginal choice. One effective way to consider where to start your bull search is to look for those breeders who are careful to record their data accurately and who have parents who are more accurate, especially with regard to the traits that are important to a specific breeding goal.
There are many producers who will form their selection decisions with reference to the heritability of traits and their association with other traits. Understanding the meaning of genetic associations is essential to this process.
Perhaps most important is to consider how these connections matter in practical terms.
Genetic associations
Genetic correlations describe how, on average, two traits tend to vary (or not vary) together. This is expressed as a number between -1 and +1. Negatively correlated traits describe situations in which, as one trait increases, there is a corresponding decrease in the other, while positive correlations describe a common increase (or decrease) in both traits.
Correlations closer to an absolute number of -1 or +1 describe cases where a change in one trait is strongly associated with a change in the other, while low numbers (closer to 0) essentially mean that for those pairs of traits there will be no pattern to how one changes with respect to the other.
Dr. Matt Wolcott From the Animal Genetics and Breeding Unit at Armidale provided an overview of genetic associations as part of a contribution to the recently published study. Bush Agribusiness’s ‘Best Agribusiness Companies 2024’ report.
Dr. Matt Wolcott
“Genetic associations are assessed as part of the development that underpins BreedPlan and are a key component of multi-trait assessment,” said Dr. Wolcott.
At the analytical level, genetic associations help maximize the information obtained from the recording made by the seed breeder.
“For producers trying to make selection decisions in arenas, trying to look at correlations between traits is not only overly complicated, it is largely unnecessary,” Dr. Wolcott points out.
As part of Matt Woolcott’s contribution to “Top Studs,” he summarizes the average heritability and genetic correlations between traits in BreedPlan’s evaluations of moderate beef breeds.
The figure below shows that genetic correlations tend to be moderate to weak, with the only strong relationships observed between some weight traits, or the two measures of fat depth (Rib and P8).
Average heritability (diagonal) and genetic correlations between trait pairs in BreedPlan evaluations of moderate beef breeds – Dr. Matt Woolcott AGBU; Source: Bush Agribusiness, Top Studs 2024. Click on chart for larger view.
What this means in practice is that while carcass weight, for example, is moderately heritable (i.e. there is potential for improvement through selection), the genetic correlation with other aspects of carcass composition (rib fat and P8, eye muscle area, retail beef production and marbling) is moderate at best, and not all in the same direction.
“In this example, there are only moderate to weak genetic correlations between carcass weight and other aspects of carcass composition, and both negative and positive correlations between carcass traits can be seen in the BreedPlan evaluation of moderate beef breeds,” explains Dr. Wolcott.
“Therefore, relying on relative carcass weight values to provide useful information about bull genetics in relation to other aspects of carcass composition would be ineffective, at best.”
Crucially, genetic associations describe what is observed on average, and they make the greatest contribution to estimating the value of breeding where records of associated traits are rare or missing.
In cases where all traits are captured in the educational objective and included in the assessment, the effect of genetic associations on educational value estimates becomes small.
Matt Woolcott’s advice to producers is to realize that “accurate recording of correlated traits will always outperform predictions of how traits co-vary, at the genetic level, as shown by their genetic associations.”
This means that the key question in evaluating a male’s suitability as a source of bulls for your herd is – do they score on the traits important to my breeding goals?
Alistair Rayner is General Manager Expansion and Operations at Cibo Labs and Director of RaynerAg. Alistair has over 28 years’ experience advising beef producers and growers across Australia. He can be contacted here or through his website www.raynerag.com.au
