DNA Study Reveals Many “Beefalo” Lack Bison Ancestry

Unlocking Fifty Years of Breeding Mystery

The Beefalo breed gained attention when breeder D.C. “Bud” Basolo established foundation herds through complex interbreeding of bison and domestic cattle. At the time, a bull named Joe’s Pride changed hands for $2.5 million, backed by a recorded pedigree placing his bison ancestry at more than one-third. However, Basolo never revealed the exact pedigree used to produce his original animals, leaving breeders and scientists with an unresolved biological question.

The American Beefalo Association’s official breed standard specifies a genetic makeup of five-eighths cattle and three-eighths bison. Historical attempts at bison-cattle crosses dating back to the early years of the twentieth century routinely encountered severe reproductive hurdles. Canadian government work cited in the research paper reported that no functional male carrying more than an eighth bison ancestry was ever observed, as artificial insemination typically produces high calf mortality and sterile male calves.

DNA Analysis of Federal Biobank Samples

To investigate what was inside the animals, Shapiro’s team turned to the United States Department of Agriculture’s National Animal Germplasm Program collection located in Fort Collins, Colorado. Researchers obtained straws of semen frozen since the 1970s and 1980s, which had been donated to the federal biobank around 2007. The sequencing project evaluated 47 registered Beefalo—including foundation animals from Basolo’s herds—alongside three majority-bison hybrids and ten commercial bison.

Using shallow sequencing with a median of 2.7 times coverage, the team analyzed over 5 million variant positions identified in gaur to avoid coverage bias. Four separate analytical approaches—including principal component analysis, admixture models, allele-sharing statistics, and chromosome-by-chromosome ancestry mapping—all pointed to the same conclusion: 39 of the 47 tested Beefalo carry zero detectable bison DNA. Only eight animals derived between 2 and 18 percent of their genomes from bison, falling short of the historical breed standard. Joe’s Pride was among the 39 animals containing no bison ancestry.

Zebu Ancestry Replaces Expected Bison Genes

While bison DNA was largely absent in the tested foundation animals, the genome survey uncovered a different genetic addition. Chromosome-mapping identified zebu ancestry in 38 of the Beefalo animals, with proportions ranging from 2 to 38 percent. Joe’s Pride, whose written pedigree listed only Hereford, Charolais, and bison, was estimated to carry about 10.5 percent zebu DNA.

The study’s authors suggest that early breeders may have deliberately incorporated zebu cattle to manipulate the physical traits of the animals. Zebu cattle share several commercially relevant characteristics with bison, including heat and drought tolerance, lower nutritional demands, and a distinct shoulder hump. Because the breed standard does not restrict the cattle lineage exclusively to taurine breeds, incorporating zebu genetics did not violate technical rules, even if it was omitted from written pedigrees.

Tracing the Y Chromosome and Backcrossing

Sex chromosome analysis clarified how small amounts of actual bison ancestry entered the eight positive animals. All tested Beefalo carried Y chromosomes associated with taurine cattle, whereas majority-bison hybrids carried bison Y chromosomes. Furthermore, the eight Beefalo with bison markers showed less of that ancestry on the X chromosome than on the autosomes, a pattern consistent with breeding bison bulls to cattle cows and repeatedly backcrossing the offspring to cattle.

Bison DNA in those eight animals appeared in long, unbroken stretches of tens of millions of base pairs, indicating recent admixture before generational recombination could break the segments apart. Conversely, zebu segments appeared smaller and more fragmented, suggesting an earlier introduction date.

Frequently Asked Questions

Did Joe’s Pride actually contain bison DNA?

No. Genome sequencing of preserved semen from Joe’s Pride showed no detectable bison ancestry, despite a written 1975 pedigree claiming he was more than one-third bison.

How much bison ancestry do modern Beefalo actually have?

According to the eLife preprint by Beth Shapiro’s team, 39 out of 47 tested historical Beefalo from foundation herds carried zero detectable bison ancestry, while eight animals carried between 2 and 18 percent.

Where did the genetic samples come from?

The research samples were sourced from frozen semen straws housed in the USDA National Animal Germplasm Program collection in Fort Collins, Colorado.

What replaced the bison DNA in these animals?

Chromosome mapping revealed that 38 of the tested animals carried zebu ancestry ranging from 2 to 38 percent, likely introduced by early breeders to enhance heat tolerance and other physical traits.