E429 When Red × Red = Black: A Holstein Breeder’s Guide to Variant Red (COPA) Genes

For decades, Holstein breeders operated on one simple rule: black dominates red. It was genetics 101—comfortable, predictable, and wrong. In 2015, researchers discovered the COPA gene, a genetic "override switch" that can make animals express red regardless of their underlying color genetics. The problem? A Variant Red bull bred to red cows can still throw 50% black calves. If that's happened in your barn and you couldn't explain it, this episode will change how you think about color inheritance—and save you from costly breeding mistakes.
Key Takeaways:
Why the traditional MC1R color model is incomplete—and what COPA changes about everything you thought you knewThe exact genetic scenario that causes Red × Red matings to produce black calves (and how to predict it)How to interpret Variant Red testing results and what the codes actually meanThe real cost of skipping color genetics testing: registration errors, angry buyers, and breeding plans built on false assumptionsWhy US and Canadian systems use different codes (DR0/DR1/DR2 vs. VRF/VRC/VRS)—and how to read them correctlyWhich operations absolutely need to test for COPA, and which can rationally skip itWhere the industry is heading on mandatory color genetics testingDeeper Dive – Why Listen:
This episode breaks down the science of epistasis—one gene overriding another—in plain language that any breeder can understand and immediately apply. You'll learn why phenotype alone tells you nothing about what's happening genetically, and why that $30 test through UC Davis VGL could save you hundreds in buyer disputes and registration corrections.
We walk through four specific mating scenarios with expected outcomes, including the critical "trap" scenario where heterozygous Variant Red bulls (N/DR) carrying hidden black genetics (E^D at MC1R) produce black calves even when bred to recessive red cows. This is the situation that's been burning breeders for years—and now you'll understand exactly why it happens and how to prevent it.
The episode also examines the industry trajectory. AI studs like Select Sires are already publishing DR codes in their catalogs. Breed associations have built the recording infrastructure. For seedstock operations and anyone marketing genetics where color affects value, understanding COPA isn't optional anymore—it's table stakes.
Whether you're a commercial producer wondering if this applies to you, or a seedstock breeder who needs to get color genetics right every time, this episode delivers actionable insights you can implement immediately.
Resources & Engagement:
The full article, "When Red × Red = Black: A Holstein Breeder's Guide to COPA," is available now at https://www.thebullvine.com/genetics/... with complete mating scenario breakdowns, testing resources, and US/Canadian code comparisons.
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