LAST week’s announcement that the Australian Brahman Breeders Association will review its selection indexes has renewed interest in how these tools are developed and used. The discussion that followed has covered a wide range of views on indexes, the assumptions behind them and the broader role of BREEDPLAN. The review provides an opportunity to revisit how indexes are developed, what they represent and how they can be used with individual EBVs.

Many breeds that publish EBVs also use selection indexes to help producers make balanced selection decisions across several economically important traits at once. These indexes are developed through BreedObject for a defined commercial production system and market.

Developing an index starts with defining a production system, including its herd structure, replacement policy, production environment, input costs, sources of income and target market. This identifies which traits influence profitability in that system and the economic value of improving each one.

BreedObject uses those economic values to determine the emphasis placed on each available EBV, taking into account genetic relationships among traits and the correlated responses expected from selection. The emphasis on an EBV is therefore not necessarily the same as the economic importance of the trait it describes.

The resulting value ranks animals as potential parents according to the expected profitability of their progeny in the production system described. It balances advantages and disadvantages across traits rather than identifying the animal with the highest figure for any one EBV. It therefore focuses on expected genetic outcomes in progeny rather than phenotype alone.

For a producer weighing growth against fertility, or carcase merit against cow size, an index performs calculations that are difficult to make consistently by scanning a page of EBVs. It brings a range of genetic information together around a commercial objective.

A high-indexing animal will not necessarily be above breed average for every EBV. Two bulls can reach similar index values through different combinations of merit. An animal can rank highly while being below average for one trait because its advantages elsewhere are worth more in the defined system. This is an expected outcome of balanced selection and needs to be interpreted in the context of the index objective.

An index should not be treated as a mating plan. Trait limits can vary with the females being joined, the production environment and the management program. A bull whose Birth Weight EBV exceeds a producer’s limit for heifers may still suit mature cows with lower birth-weight genetics, provided his Calving Ease EBVs and the associated risk are acceptable. Market specifications are generally less flexible, although production systems differ in the time and resources available to reach them.

An index does not describe an animal’s phenotype, guarantee the performance of every calf or represent every beef enterprise. It estimates relative genetic merit for profit under a defined production model. It is not a forecast of enterprise profit, and its value should not, on its own, be treated as the maximum premium a producer can pay for a bull. A purchasing decision must also account for the number of cows joined, working life, accuracy, timing of returns and the circumstances of the business.

In practice, producers should first choose the index that most closely matches their production system and market, then consider any individual EBV thresholds that matter to their herd. Accuracy, structural soundness, temperament, reproductive fitness, genetic conditions and pedigree remain an integral part of the selection decision.

This does not mean indexes should be treated as permanent or beyond scrutiny. Their economic and production assumptions should be reviewed as markets, prices, costs, management systems and industry priorities change.

Breed societies periodically review or replace their selection indexes. In 2022, the Brahman breed replaced the Jap Ox and Live Export indexes with the Central Production and revised Live Export indexes. In 2024, Herefords Australia replaced four indexes with two: the Sustainability Production Index and the MSA Production Index. Index development and revision commonly include discussion with breed members, technical specialists and other industry participants. Changing an index is therefore a normal part of maintaining its commercial relevance.

Index reviews generally consider whether production assumptions remain representative, whether prices and costs reflect likely commercial conditions, and whether the target market is accurately defined. They can also examine whether important traits are missing, how sensitive animal rankings are to changes in key assumptions and whether the expected response to selection remains balanced. If the existing indexes do not adequately represent the range of production systems within a breed, an additional index or a more suitable replacement may be appropriate.

The interpretation of an index also depends on the EBVs that underpin it and the way BREEDPLAN analyses the available information.

Contemporary groups allow animals managed under similar conditions to be compared so that environmental and management effects can be separated, as far as possible, from genetic differences. They are essential to the analysis, but they do not confine EBVs to use within a single herd. BREEDPLAN combines performance, pedigree and, where available, genomic information across participating herds. Genetic links through common sires, related animals and the movement of genetics connect those groups within the wider breed analysis. The strength of across-herd comparisons depends on the quantity, quality and connectedness of that information.

Nutrition, pasture and season have major effects on reproductive performance. Nutrition affects how fully females express their genetic potential, while EBVs estimate genetic differences between animals once identifiable environmental effects have been accounted for. Commercial performance reflects both environment and genetics.

A decision to review an index does not mean the development or publication process has failed. Reviews help keep indexes relevant as production systems, costs and markets change. An unexpected ranking can often be better understood by returning to the index objective and the balance of EBVs contributing to the result. An EBV estimates an animal’s genetic merit, expressed through expected differences in its progeny, while an index combines those EBVs to estimate its overall genetic contribution to profitability across a defined production system. Neither is intended to describe phenotype alone.

Confidence in these evaluations depends on the quality and breadth of the information available. Accurate and consistent records from a range of herds and production systems strengthen comparisons, increase confidence in EBVs and allow assumptions to be tested. Continued performance recording therefore provides the evidence needed to identify weaknesses, assess alternatives and support further progress.

A useful review brings producer experience and commercial observations together with technical and economic evidence. It can then assess whether the underlying assumptions remain appropriate, whether the production systems are still relevant and whether any changes would make the indexes more useful to breeders and commercial producers.

Alastair Rayner is the Strategic Account Manager for Southern Australia with Vytelle and Principal of RaynerAg. He has over 30 years’ experience advising beef producers and graziers across Australia. Alastair can be contacted here or through his website: www.raynerag.com.au