Thirty-nine of the 47 registered Beefalo whose genomes were sequenced carry no detectable bison ancestry, including the foundation bull that sold for $2.5 million in 1975 and whose pedigree recorded h

Key Points:

• A genome-wide study of 47 registered Beefalo, including foundational herds, found that 39 animals have no detectable bison ancestry, contradicting the breed standard of three-eighths bison and five-eighths cattle.
• The study revealed significant zebu cattle ancestry (2-38%) in most Beefalo, including Joe’s Pride, whose pedigree claimed over one-third bison but was estimated to have about 10.5% zebu instead.
• Historical reproductive challenges, such as high calf mortality and sterile male hybrids, have long hindered stable bison-cattle crosses, explaining why a stable three-eighths bison herd was never established despite breed claims.
• Genetic evidence shows bison ancestry entered Beefalo through bulls bred to cattle cows, with backcrossing to cattle diluting bison genetic contributions over generations, supported by patterns in sex chromosomes and ancestry block lengths.
• This research, based on preserved semen samples from the 1970s-80s and published as a peer-reviewed preprint, challenges the accuracy of Beefalo pedigrees and calls for broader sampling of current herds to further clarify breed composition.