The video depicts an annual bison roundup at a state park in far southwestern Minnesota near the South Dakota border. From it I learned that some of the bison who survived the great slaughter of the settlement era have DNA that is "contaminated" with ranch cattle DNA. Some effort has been made to cull current stock to restore the genetic purity of the remaining animals.
During the population bottleneck, after the great slaughter of American bison during the 1800s, the number of bison remaining alive in North America declined to as low as 541. During that period, a handful of ranchers gathered remnants of the existing herds to save the species from extinction. These ranchers bred some of the bison with cattle in an effort to produce "cattleo." Accidental crossings were also known to occur. Generally, male domestic bulls were crossed with buffalo cows, producing offspring of which only the females were fertile. The crossbred animals did not demonstrate any form of hybrid vigor, so the practice was abandoned. The proportion of cattle DNA that has been measured in introgressed individuals and bison herds today is typically quite low, ranging from 0.56 to 1.8%. In the United States, many ranchers are now utilizing DNA testing to cull the residual cattle genetics from their bison herds. The U.S. National Bison Association has adopted a code of ethics which prohibits its members from deliberately crossbreeding bison with any other species.A hat tip to reader Lloyd Stanley for bringing the video to my attention.