An analysis of early Beefalo animals found little to no bison DNA, researchers reported on June 10 in the journal eLife. The findings contradict breed standards established by the American Beefalo Association.

Beth Shapiro, an evolutionary biologist at the University of California, Santa Cruz, and her colleagues analyzed preserved semen samples from 47 Beefalo animals. Most of these samples were collected in the 1970s and 1980s, including some from the original Beefalo herd. Out of the 47 animals analyzed, 39 contained no detectable bison ancestry. Eight of the Beefalo animals analyzed contained some bison DNA, but their levels were less than the breed standard defined by the American Beefalo Association. The association defines the breed standard as three-eighths bison ancestry.

Shapiro stated, "It was a surprise to us to discover that most of the Beefalo individuals we sequenced did not have detectable bison ancestry." She added, "While there clearly has been some gene flow between the two species since cattle were brought to North America, it has been far less frequent and far less consequential than previously believed."

The American Beefalo Association disputes the study's results. Dan Stricker, president of the American Beefalo Association, said, "We have serious concerns that the samples used in Dr. Shapiro's study do not accurately represent modern, registered Beefalo that have been selectively bred for bison traits over many generations." Stricker also stated that all "full-blood" Beefalo in the American Beefalo Association registry are required to pass DNA tests confirming their bison ancestry. These DNA tests for registration are conducted through laboratories at the University of California, Davis, and Neogen Genomics in Edmonton, Alberta.

Jonas Oppenheimer, an evolutionary biologist at the Centre for Paleogenetics in Stockholm and a coauthor of the study, stated that it is unlikely that present-day Beefalo individuals contain more bison ancestry than their founders. Most wild bison possess some amount of cattle genes.