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Considerations for Winter Bison Management

Updated May 04, 2023
Professional headshot of Pete Bauman

Pete Bauman

SDSU Extension Natural Resources and Wildlife Field Specialist

Written collaboratively by Pete Bauman and Heidi Carroll, former SDSU Extension Livestock Stewardship Field Specialist & Beef Quality Assurance Coordinator, with review and contributions from Dr. Vern Anderson, NDSU Animal Scientist at the Carrington Research Extension Center; Gail Griffin of the Minnesota Buffalo Association; and Mary Miller (MS) of The Nature Conservancy.

Home on the Range

South Dakota is well known for its strong livestock industries. Cattle, sheep, poultry, hogs and horses are common across the state, and three of these rely heavily on South Dakota’s grasslands. What surprises many South Dakotans is the strength of one of our other grass-based livestock industries. In the world of bison, South Dakota is at the helm, leading the nation in total bison production. According to the 2013 annual South Dakota Department of Agriculture report, South Dakota had 179 bison farms and was home to nearly 39,000 bison (based on 2007 data). Various estimates indicate the North American bison population is approaching one half-million animals, and approximately one in ten bison on the continent reside within South Dakota’s borders! In addition to our private enterprises, South Dakota is also home to state, federal and tribal bison herds primarily managed for grassland conservation and retention of bison genetics.

Bison management in North America is quite diverse, and managers implement various philosophies when raising these icons of the plains. A major challenge for bison managers is the lack of research data on which to base nutrition requirements and management techniques. Years of experience, observation and discussion amongst producers primarily guides decisions. The purpose of this article is not to debate how bison are raised, rather we aim to simply provide food for thought for managing bison herds during a South Dakota winter.

Seasonal Responses

Bison are native to South Dakota and are extremely well adapted to our climate, topography and native forages. However, bison are not cattle. Although many of the tools and techniques developed for cattle management have been adapted for bison, there are some stark differences between the two species that producers should consider when managing bison on winter range. During winter months, the bison’s metabolism generally slows down, resulting in lower maintenance energy requirements than in the summer months. Behaviors to conserve body heat and energy, such as moving less to disturb the insulative coat, may be observed. This may be accompanied by breathing and heart rates slowing to minimize cold intake. Bison cows generally gain weight in summer and late fall to prepare fat reserves for winter survival and fetal development. During winter, it is normal for bison cows to lose up to 10% of their body weight (~100 pounds) in mid-to-late gestation as part of their natural reproductive cycle.

    Sustainable Winter Grazing

    Small group of bison grazing winter pasture.
    Courtesy: Canva

    Even though bison are well adapted to our climate, their basic needs must be met to ensure adequate herd and individual health. Therefore, the predominant factor in winter grazing bison is ensuring adequate forage availability while considering overall long-term range health and maintenance. Simply stated, it is possible to ‘overgraze’ winter rangelands, and careful planning is necessary. Overstocking winter range can lead to negative impacts to individual plants, potentially damaging the base of the plant and robbing it of vital nutrients for spring growth. Severe winter grazing can expose soil, leading to future issues with invasive species, especially in dry regions. Overall, mismanagement of winter range can impact ranch economics through increased input costs in animal health, feedstuffs, reduced production and future weed control. However, when managed correctly, grazing bison on winter range can be a viable option for controlling feed costs and ensuring herd health.

    When determining appropriate stocking densities for your winter rangeland and estimating animal intake, bison are comparable to beef cattle in that a 1,000-pound bison cow is considered one animal unit (AU). As mentioned earlier, bison have seasonal changes in their energy requirements, so dry matter intake (DMI) may drop as low as 2.0% or less of their body weight per day. However, using a standard range management estimate of 2.6% body weight (~26 pounds DMI per day), which doesn’t account for the seasonal fluctuations in energy requirements, will help maintain plant diversity and sustainable forage production while meeting the animal’s intake needs. Keep in mind that dry matter intake is simply the weight of the feed without water, so intake may fluctuate based on the nutrient density of the available forages. Thus, measurements of the forage production and quality of winter pastures is recommended for an accurate stocking plan. Due to their build and heavy hair coat, determining the weight of bison can be difficult when calculating forage needs. Also important is realizing that forage degradation due to weather, breakage from wind and compaction from snow can decrease available winter forage. Total forage availability is determined at the time the range goes through fall dormancy, so consideration for biomass loss due to winter weather is critical if the range is to ‘carry’ the herd through the winter months.

    Water, Shelter and Room to Roam

    Generally speaking, bison tend to winter well in larger pastures. During typical South Dakota winters, bison can usually meet their water needs if adequate clean snow is available. However, in dry, cold winters without snow cover, bison will require access to fresh water. Water needs can be met via natural wetlands and riparian areas, as long as the water stays open. Managers should monitor use of large or deep-water bodies, as bison can easily break through thin ice. Regardless of the source, managers should ensure a constant source of water to guarantee the bison’s needs are met since water is the first limiting nutrient in the diet. A bison on winter range requires no manmade shelter because of its dense coat. Instead, it will utilize draws or topographic features during inclement weather when necessary.

    Consideration for bison’s strong social hierarchy is important. Overall, adequate forage is important, but providing enough pasture space is also necessary to reduce stress from competition and will also reduce damage to fences and gates.

    Supplemental Feeding/Nutrition

    The bison rumen is well adapted to a rangeland diet and requires minimal supplementation during the winter if animals have access to adequate pastures with reasonable plant diversity. Managing herd size and matching it to pasture production is an important skill and can help limit the additional costs of purchased feeds to meet the bison’s nutritional needs. It should be noted that bison cows will boost their forage intake in preparation for calving and lactation, and this increase in forage need may occur while pastures are still dormant. This should be considered when planning stocking rates for the winter to ensure adequate pasture allocation for each individual. Free choice mineral and salt supplementation may be desirable to allow animals to make up any diet deficiencies.

    If pasture is limited or if stocking density is too high in relation to forage availability, feed supplementation may be necessary. The potential impacts on the range from concentrating animal activities should be monitored and evaluated when placing supplemental feeds within pastures. To protect the integrity of the range in these situations, reduced bison access to native pastures to minimize unnecessary damage is recommended. One option is to choose a smaller pasture or area to winter the herd on while feeding supplemental hay in order to limit the negative impact on the entire pasture. Another consideration is to reduce herd size to regain balance with available forage if winter grazing is to support the herd long-term. In more-confined situations, adequate forage should be made available and dispersed appropriately so even subordinate herd members have access to feed.

    In the event of severe weather or prolonged cold, energy or protein supplementation may be necessary to help meet maintenance requirements. As previously mentioned, some seasonal weight loss is normal, but good management is important to catch severe weight loss that may indicate an internal parasite problem. Consider body condition scoring the herd in the fall at weaning and in the spring during calving to help monitor performance or testing fecal samples to monitor parasite loads. In any case, supplementation should be suited to your pasture conditions, forage diversity, available feedstuffs, animal condition and marketing plan.

    Basic Animal Health and Handling

    Bison are hardy and have maintained higher levels of disease resistance than domestic livestock. In late fall/early winter, many ranchers wean calves and work their herds. This can be the most-stressful time of year for the herd. Herd health plans may include deworming, vaccinations, blood sampling, and pregnancy checking depending on the overall herd management strategy or potential disease threats in the area. Because of bison’s strong social hierarchy, additional stress can be incurred if that hierarchy is disrupted or if animals are isolated. Understanding bison’s natural behaviors is the key to calm handling to prevent injury and promote overall health. A critical factor in successful bison management is to minimize handling time in confined spaces. Handling stress can lead to decreased animal performance, increased illness, increased damage to facilities and unnecessary injury to the bison or the stockmen. Essentially, bison in well-managed environments tend to thrive with minimal human intervention.

    This is only a brief introduction to one of the less-represented livestock species that has a rich South Dakota history on our native rangelands. Visit our website in the future for more information on bison in South Dakota.

    For more information on range management, please contact Pete Bauman, SDSU Extension Natural Resources and Wildlife Field Specialist. For more information on animal handling or bison resources, please contact Heidi Carroll, SDSU Extension Livestock Stewardship Field Specialist & Beef Quality Assurance Coordinator.

    Additional Resources

    For more information on the history and management of bison, see the following resources: