By Dr. James Derr, Texas A&M University
Geneticists at Texas A&M University College of Veterinary Medicine have conducted DNA testing on more than 40,000 bison from public and private bison herds. They have developed two genetic assays to uncover past evidence of hybridization between bison and domestic cattle. The first genetic test involves mitochondrial DNA (mtDNA) which is only passed from mother to offspring. You might remember from biology class that the mitochondria is referred to as the powerhouse of the cell because it is critical for energy conversion. Following a hybridization event between a bison male and a domestic cattle female, cattle mtDNA will persist in that lineage as long as these bison mothers produce daughters. Since the male does not contribute any mtDNA to his offspring, this domestic cattle marker is never “diluted out”. These studies have found that approximately 6% of bison in North America have domestic cattle mtDNA. However, there are many bison herds with no cattle mtDNA and other examples of bison herds with 100% cattle mtDNA. Importantly, bison with cattle mtDNA are, on average, smaller than bison with the correct bison mtDNA.
The second test developed by researchers at Texas A&M University involves markers from the nuclear genome (these markers are called microsatellites), and they are equally contributed by both the mother and the father to each offspring. This test is based on 14 different markers from the bison genome, and it is was developed to detect hybridization between these two species in bison herds. Importantly, this test is not designed to assure individual bison are totally free of cattle genetics. However, this test is very powerful if used correctly to document past hybridization in bison herds. Results of this testing over the last 20 years have found, on average, the majority of bison across North America have between one and three percent cattle genes in their nuclear genomes. However, with the completion of the bison genome project in 2015, a much more powerful Single Nucleotide Polymorphism (SNP) genetic test is in development that will expose the exact levels of cattle genetics present in a bison and provide information on the function, or dysfunction, of cattle genes found in individual bison. In addition to identifying levels of domestic cattle introgression, these genetic technologies also provide important management tools for bison such as parentage testing, inbreeding analysis and ancestry determinations back to major public herds and historical herds that existed at the apex of the species bottleneck in the late 1800s.
The ability to document past hybridization between these two species is essential for species conservation efforts that focus on saving important bison genetic diversity and to assist bison owners and managers in managing away from high levels of domestic cattle introgression in their bison herds. Appropriate use of genetic technology is an important tool to ensure responsible stewardship of this species by those concerned with long-term species conservation.
For a producer, the decision to use this technology as part of your management plan must be based on many different factors. However, you should know that all of the Federal and most of the State bison herd managers have employ genetic testing to cull animals with a significant degree of cattle genetics as part of their herd management process, and hundreds of private bison owners have also taken advantage of these scientific tools.