AS the spring bull selling season gains 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 driven on the basis of profit-based breeding objectives and the need to make improvements in the genetic makeup of a herd to achieve a production outcome.

The opportunity to shape selection decisions based on access to performance records has helped producers increase confidence in their overall choices. However, there are some important caveats that need to be included in the decisions that are made.

One of the first is to objectively consider the performance recording that is being undertaken by a particular prefix or seedstock producer. While many bull breeders will be offering animals this year with EBVs, not all producers will have exhibited a similar degree of rigour in recording and submitting data for analysis.

While recording large amounts of data will result in improvements in accuracies, equally there is a potential for producers to record only one or two traits, or even just submit a DNA sample and still obtain EBVs for their sale bulls. The result is a series of EBVs that can be used in a selection decision, however it is important to note these EBVs based on lower levels of recording will tend to have lower accuracies.

In practice, lower accuracy means there is greater potential for the EBVs to change as more data is collected, and so a bull that may meet a producer’s requirements on first consideration can easily fall out of consideration as more becomes known about him and his genetics.

For producers seeking to create a shortlist of bulls to physically inspect, appreciating accuracies may be the difference between purchasing a bull that is very suitable and one which later proves to be a marginal choice. An effective way of considering where to start looking for bulls is to look for those breeders who are thorough in their recording and who have sires with higher accuracies, particularly for the traits that are important to a specified breeding objective.

There are many producers who will shape their decisions on selection with some reference to the heritability of traits and their correlation with other traits. Understanding what genetic correlations mean is fundamental in this process.

Perhaps even more important is reflecting on how important these correlations are in a practical sense.

Genetic correlations

Genetic correlations describe how two traits, on average, tend to (or not to) vary 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 figure of -1 or +1 describe cases where a change in one trait is strongly associated with a change in the other, while lower figures (closer to 0) basically mean that for those pairs of traits there will be no pattern to 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 from Bush Agribusiness.

Dr Matt Wolcott

“Genetic correlations are estimated as part of the development which underpins BreedPlan and are one of the key components of its multi-trait evaluation,” Dr Wolcott said.

At the analytical level, genetic correlations help to maximise the information obtained from the recording that seedstock breeders undertake.

Dr Wolcott notes that “for producers attempting to make selection decisions in the yards, attempting to consider the correlation of traits is not only extremely complex, but is largely unnecessary.”

As part of Matt Wolcott’s contribution to “Top Studs”, he summarised average heritabilities and genetic correlations between traits in the BreedPlan evaluations for temperate beef 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 the two measurements of fat depth (Rib and P8).

Average heritabilities (on the diagonal) and genetic correlations between pairs of traits in BreedPlan evaluations for temperate beef breeds – Dr Matt Wolcott AGBU; Source: Bush Agribusiness, Top Studs 2024. Click on graph for a larger view.

What this means in practice is that while carcase weight, for example, is moderately heritable (meaning there is potential for improvement through selection), the genetic correlation with other aspects of carcase composition (rib and P8 fatness, eye muscle area, retail beef yield and marbling) are moderate at best, and are not all in the same direction.

Dr Wolcott explains this saying, “In this example, there is only moderate to weak genetic correlations of carcase weight with other aspects of carcase composition, and both negative and positive correlations can be observed between the carcase traits in the BreedPlan evaluation for temperate beef breeds.

“Relying on carcase weight EBVs, therefore, to provide useful information about a bull’s genetics for other aspects of carcase composition will be ineffective, at best.”

Critically, genetic correlations describe what is observed on average, and they make the largest contribution to breeding value estimation where records for correlated traits are sparse or missing.

In cases where all traits in the breeding objective have been recorded, and included in the evaluation, the impact of genetic correlations on breeding value estimations becomes negligible.

Matt Wolcott’s advice to producers is to recognise that “accurate recording of correlated traits will always trump the expectations of how traits vary in common, at the genetic level, described by their genetic correlations.”

This means that a key question in assessing a stud’s suitability as a source of bulls for your herd is – Do they record the traits which are important to my breeding objectives?”

Alastair Rayner is the General Manager of Extension & Operations with Cibo Labs and Principal of RaynerAg.  Alastair has over 28 years’ experience advising beef producers & graziers across Australia.   He can be contacted here or through his website www.raynerag.com.au