From the 30+ million bison roaming the Great Plains when Louis and Clark traveled the Missouri River, by 1889, scarcely more than 800 free-roaming animals were documented. Current populations were primarily restored through the descendants of less than 200 animals used to establish five private herds owned by U.S and Canadian ranchers. Today there are more than 500,000 in public and private herds.
In North America, bison are recognized as an important species for maintaining grassland diversity, especially in land management systems that simulate the historical grazing-fire interaction and create a mosaic of habitat for other wildlife. This important ecological function has lead conservation organizations to regard bison primarily as an ecological management tool.
However, with approximately 4,800 bison on nine preserves, The Nature Conservancy may have an important role to play in the genetic conservation of bison as a species.
Tail hairs are providing insight into the genetic makeup of the Conservancy’s bison herds.
With the help of funding from the RJKOSE Foundation, our herds and other conservation bison herds underwent studies to examine the degree of cattle interbreeding and genetic diversity within and among herds.
A major obstacle to the conservation of bison is the discovery that most public and private herds previously evaluated contain evidence of past interbreeding with domestic cattle.
The introgression of cattle DNA into bison herds occurred more than 100 years ago, when bison were at the brink of extinction and small herds were maintained on private ranches. Ranchers began experimentally breeding the bison with cattle in an attempt to engineer hardier livestock.
Most of the bison in existence today are descendants of the 500 bison in these private herds.
The results of this project will help guide herd management as well as long-term conservation of the bison genome. Coordinated efforts must be made to prevent the introduction of domestic cattle genetics and loss of genetic diversity.
Results for North Dakota and South Dakota
Bison from two Conservancy herds in North Dakota and South Dakota were evaluated for cattle interbreeding by pulling tail hairs from the animals. The DNA in the hair was analyzed and archived by Texas A & M University.
There were two rounds of testing. The first was to look for mitochondrial DNA cattle genes (maternally inherited). The second was a nuclear DNA test (inherited from both parents).
In South Dakota, 327 bison in the Ordway Prairie herd were tested. Cattle mitochondrial DNA was found in 1.2% of the herd while cattle nuclear DNA markers were found in 5.8% of the herd. The bison with cattle mitochondrial DNA have been removed from the herd.
In North Dakota, 130 bison in the Cross Ranch herd were tested. Introgression of cattle DNA was found in both mitochondrial (5.3%) and nuclear tests (14.6%).
The testing also showed that the bison at Ordway Prairie and Cross Ranch have genetic lineages known to occur at Custer State Park in South Dakota, Fort Niobrara NWR in Nebraska and Teddy Roosevelt National Park in North Dakota.
“These results are about the same as most bison herds tested to date and were not unexpected since most of our herd originally came from Custer State Park and Teddy Roosevelt National Park,” said Eric Rosenquist, Cross Ranch preserve manager.
The results of this study tell us what level of cattle introgression exists in these herds. Archived DNA sources collected during this study will be extremely valuable in evaluating genetic diversity and relationships among herds in future studies.
Bison herds with cattle introgression harbor unique and valuable bison genetics, requiring preservation and careful management to ensure long-term species viability—for both genetic conservation and the utilization of bison in native grassland restorations.
The Conservancy also owns a herd located at Lame Johnny Creek Ranch in western South Dakota. These bison originated from Wind Cave National Park and are considered to be an unhybridized herd; blood and tail hair DNA tests have found no evidence of cattle genes.
In October 2008, the Conservancy transferred 28 bison from Lame Johnny Creek to its Broken Kettle Grassland Preserve in western Iowa to establish a new herd.