Updates to BBR Reference Population

In April 2025, all animals will receive a new Breed Base Representation (BBR) estimation based on updated business rules for selecting purebred bulls in the BBR reference population. CDCB is now able to apply more refined business rules to better identify purebred animals for the BBR reference population, due to the increasing availability of genotyped animals, along with advancements in data quality, methodologies, and technology (such as more complete pedigrees and the introduction of constructed IDs).

The BBR reference population will now be selected from the genotyped, progeny-tested bull population (minimum 10 daughters) who are enrolled (excluding bulls with status codes C and N) with complete pedigree and classified as purebred within each breed of evaluation.

• Purebred bulls must have a pedigree-based heterosis value ≤ 1% (rounded to the nearest integer.
• A complete pedigree is defined as a pedigree with all ancestors identified for four generations. Animals with constructed IDs in their four-generation pedigree are disqualified.
• Exceptions
  1. All breeds (except Jersey): Bulls born before 2000 with more than 1,000 daughters in Holstein or more than 200 daughters in other breeds are exempt from the pedigree completeness rule. This accommodates older but influential bulls with partially complete pedigrees. Per an agreement with AJCA, this rule does not apply to the Jersey breed.
                 2. Jersey breed: All animals with “JX” at the beginning of their name are automatically disqualified from the reference population.
                  3. Brown Swiss breed: Intergenomics bulls with MACE proofs are treated equivalently to enrolled progeny-tested bulls.

     To assess the impact of these updates, CDCB staff conducted a test run using a BBR reference population based on data available in August 2024. This test was applied to most animals included in the December 2024 evaluation, revealing that the percentage of animals receiving a new BBR value varies across breeds—from a maximum of 25% in Ayrshire to a minimum of 1% in Holstein.

     Because the new methodology improves the detection of animals with non-purebred ancestors, the update will generally lead to a decrease in BBR values across breeds and the consequent exclusion of some animals from the evaluation reference population and/or purebred evaluations. Animals with the most significant changes in BBR values are typically those that were previously part of the BBR reference population but are no longer included, as well as those with weak connections to the current BBR reference population, primarily foreign animals and older to very old animals. Changes in BBR will impact PTAs, particularly when animals are removed from the reference population or when their BBR drops below the 90% threshold required for calculation using single-breed SNP effects.