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From Milk EBV to Maternal Weaning Weight EBV

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From Milk EBV to Maternal Weaning Weight EBV

Wagyu-Specific Improvement in Maternal Trait Evaluation

Introduction

One of the most important changes accompanying the Australian Wagyu Association’s (AWA) transition from Estimated Breeding Values (EBVs) to Wagyu Breeding Values (WBVs) is the replacement of the long-standing Milk EBV with a new trait: Maternal Weaning Weight WBV.

While often referred to as “Milk,” the prior EBV was never a direct measure of milk production. Advances in Wagyu-specific data, modelling, and biological understanding now allow AWA to more accurately describe and evaluate maternal performance through a trait that better reflects what is actually observed in Wagyu production systems

 

What the Milk EBV Represented

In BREEDPLAN, the Milk EBV was defined as the maternal contribution to a calf’s 200-day weight, not milk yield itself. This contribution includes:

  • Milk production
  • Maternal behaviour and temperament
  • Mothering ability
  • The dam’s ability to support calf growth up to weaning

Over time, the term “Milk” led to widespread misunderstanding, with many breeders interpreting the EBV as a direct estimate of lactation performance.

 

Limitations of the Prior Milk EBV in Wagyu

As AWA’s Wagyu dataset expanded, several technical limitations of the Milk EBV became evident resulting from inaccurate trait relationships.

Analysis of Wagyu data showed that the BREEDPLAN Milk EBV had little to no meaningful genetic relationship with most growth, fertility, and carcase traits, except for birth weight measures and gestation length.   This pattern did not align with observed Wagyu performance in commercial and seedstock herds. Anecdotal and performance-based feedback from Wagyu breeders consistently indicated that Milk EBVs were often a poor predictor of actual maternal performance observed in the paddock.

 

Why Maternal Weaning Weight Is a Better Trait

The Maternal Weaning Weight WBV replaces the Milk EBV to more accurately describe what is being measured and to a Wagyu-specific underlying genetic model.

A Clearer Biological Definition

Maternal Weaning Weight represents the maternal genetic effect on calf growth to weaning, independent of:

  • The calf’s own growth genetics
  • Environmental and management effects

This definition removes ambiguity and aligns the trait name with its biological meaning.

Wagyu-Specific Genetic Parameters

Unlike the Milk EBV, Maternal Weaning Weight WBVs are calculated using:

  • Wagyu-only heritabilities and genetic correlations
  • Full multi-trait models incorporating growth, fertility, and carcase traits

 

As a result, Maternal Weaning Weight shows:

  • Positive genetic relationships with growth and fertility traits
  • Expected relationships with gestation length
  • Slight negative relationships with some marbling traits, reflecting real biological trade-offs in Wagyu systems

 

Relationship Between Milk EBVs and Maternal Weaning Weight WBVs

Comparative analyses demonstrate that Milk EBVs and Maternal Weaning Weight WBVs are strongly but not perfectly correlated.

Milk to maternal weaning weight

Figure 1. Distribution and Correlation of Milk EBVs (x axis) and Maternal Weaning Weight WBVs (y axis) for all animals.

 

Across the entire population, the correlation between Milk EBVs and Maternal Weaning Weight WBVs is approximately 0.8, indicating that animals ranked highly for Milk generally remain strong maternal animals.  However, the weaker correlation means:

  • Some animals re-rank significantly
  • Differences are most evident in animals with lower EBV accuracy
  • High-accuracy, widely used sires show stronger alignment (correlations ~0.85)

These re-rankings reflect changes in the genetic parameters within AWA’s new Wagyu-specific model.

 

Practical Implications for Breeders

What Stays the Same

  • The trait still measures maternal contribution to calf growth to weaning
  • Interpretation remains comparative (higher = stronger maternal effect)
  • Accuracy remains a key consideration in selection decisions

What Improves

  • Clearer trait definition and communication
  • Better alignment with observed paddock performance
  • More reliable selection for maternal functionality without unintended bias
  • Improved balance between maternal performance and carcase outcomes

 

Why This Change Is Only Possible Now

The replacement of Milk EBV with Maternal Weaning Weight WBV is only possible because AWA now has:

  • A much larger Wagyu-specific dataset
  • Substantially increased genomic coverage
  • Independent control of genetic evaluation models
  • The ability to update parameters based on Wagyu data alone

 

Conclusion

The transition from Milk EBV to Maternal Weaning Weight WBV represents a refinement in maternal trait evaluation. The prior Milk EBV was the best available tool at the time, but advances in data, genomics, and analytical capability now allow AWA to deliver a more biologically accurate, Wagyu-specific maternal trait.

Important Notice and Disclaimer

It is very important that you appreciate when viewing the AWA database that the information contained on the AWA database, including but not limited to pedigree, DNA information, Estimated Breeding Values (EBVs) and Index values, is based on data supplied by members and/or third parties.

Whilst every effort is made to ensure the accuracy of the information reported through AWA, AWA officers and employees assume no responsibility for its content, use or interpretation. AWA disclaims all liability (including without limitation, liability in negligence) for all expenses, losses, damages and costs you may incur as a result of the use by you of the data on this AWA database and the information supplied by ABRI and AGBU being inaccurate or incomplete in any way for any reason.

Regarding EBVs and Index values, it is very important to appreciate, and you need to be aware that:

  • EBVs are derived using Wagyu Single Step BREEDPLAN technology developed independently by the Animal Genetics and Breeding Unit (AGBU), using the information contained within the AWA database.
  • AGBU is a joint venture of NSW Department of Primary Industries and the University of New England, which receives funding for this purpose from Meat and Livestock Australia Limited.
  • AWA relies solely on advice provided by AGBU and ABRI in accepting Wagyu Single Step BREEDPLAN software.
  • EBVs published in Wagyu Single Step BREEDPLAN are estimates of genetic potential of individual animals and may not reflect the raw animal phenotype.
  • EBVs can only be directly compared to other EBVs calculated in the same monthly Wagyu Group BREEDPLAN analysis.

 

Regarding pedigree and DNA testing results submitted to the AWA, it is very important to appreciate, and you need to be aware that:

  • Animals whose registration identifiers start with PED are Pedigree Recorded Animals. What this means is that the details which Australia Wagyu Association Limited (AWA) used to register the animal were obtained from a Recognised Wagyu Registry Organisation – in other words a Wagyu breed association based outside of Australia. AWA has not independently verified the information with respect to the animal or the details recorded about the animal. You should read AWA’s by-laws which sets out details regarding the definition of a Pedigree Recorded Animal.
  • Future events cannot be predicted accurately. AWA makes no statements, representations or warranties as to the accuracy or completeness of, and you should not rely on, any information contained in the registration details of this animal or their capability to achieve any purpose. AWA disclaims all liability (including without limitation, liability for negligence) for all claims, expenses, losses, damages and costs you may incur as a result of the information set out in the registration details of this animal for any reason being inaccurate or incomplete in any way or incapable of achieving any purpose.
  • Pedigree and DNA data submitted and supplied to AWA may have errors in it which cannot be detected without further DNA testing.
  • Technology may have advanced since a particular test was undertaken so that previous inaccuracies which were not detectable are now able to be detected by current testing technology.
  • AWA estimates that less than 1% of the pedigree entries, ownership or breeding details in the AWA Herdbook may have errors or which may be misleading. For this reason, users ought to consider if they need to obtain independent testing of the relevant animal (if possible) to ensure that the data is accurate.

 

Regarding prefectural content, it is very important to appreciate, and you need to be aware that:

  • Prefectural content is based on the estimation of prefectural origin from Japanese breeding records of 201 foundation sires and 168 foundation dams. As genotype-based parent verification is not used in Japan, and full Japanese registration certificates are not available for all foundation animals, exact prefectural composition for these sires and dams cannot be validated.
  • The calculation of prefectural content for Australian Herdbook animals relies on the accuracy of pedigree records and DNA samples provided by AWA members.
  • The reporting of prefectural content for animals within the AWA Herdbook relies on the calculation provided by ABRI.

If you consider that you do not understand or appreciate the nature and extent of the data provided on this website or the EBVs of a particular animal, then AWA strongly recommends that you seek independent expert advice.

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