Dormant Season GrazingWritten by Rachel Mealor
By Rachel Mealor, UW Extension Range Specialist
Throughout many parts of Wyoming, during late fall and early winter, we’ve experienced mild temperatures with fairly limited snowfall – okay, maybe up until the last few weeks. Many livestock operators have likely taken advantage of this opportunity by grazing their livestock on dormant vegetation. With this in mind, it’s relevant to revisit dormant season grazing from an ecological perspective.
Because grasses are the dominant plant consumed by cattle and horses, particular attention will be given to their growth and development throughout this article.
A short discussion of grass growth will help clarify the effects of grazing. Grasses have growing points that are located at the base of the plant when it is in the vegetative state. The growing point then becomes elevated as it matures into the reproductive phase.
This is important because if the leaves of a grass plant are removed while it is in the vegetative state during the growing season, it has to utilize nutrients from its root system to form another tiller, or individual stem. At that point the process has to start again where the tiller goes from the vegetative state to the reproductive state again, if precipitation and temperatures are conducive for growth to occur.
Understanding this concept can help land managers develop grazing strategies to manage or manipulate their vegetation to reach their goals for specific areas or pastures.
So, what does this have to do with dormant season grazing? Dormant season grazing is defined as grazing during that time period when a plant is inactive or not growing between late fall and green-up in spring. Dormant season grazing is often considered a less damaging time of year for grazing grasses, and there has been much research regarding nutritional management of cattle grazing during this period.
However, there has been less literature devoted to specific ecological impacts of winter grazing.
An interesting article was published regarding dormant season grazing from an ecological perspective. Some of the objectives of the study were to determine the impacts of winter grazing on herbage production and growth rate of dominant grass species over the short term. Although the study took place in western North and South Dakota, many of the systems they were studying are quite similar to places in Wyoming, with a wheatgrass-needlegrass vegetation type.
Consistent with other research, they reported positive effects on herbage production with increased levels of herbage removal during the dormant season. In other words, pastures that experienced dormant-season grazing produced more forage the following growing season. Dormant season defoliation was not detrimental and the reduction in litter on the soil surface may be important to subsequent years’ plant growth and forage production.
The study also concluded by reporting that during May through November in 2000, seasonal forage availability declined considerably between peak production and the beginning of the winter grazing season. Given this information, they suggested that stockpiling of forage throughout the growing season for use in late fall or winter results in lost herbage production potential.
Along with that, animal unit months (AUMs) per hectare (ha) for winter-only grazing areas were severely reduced compared to season-long grazing use. They suggest incorporating a brief early-summer grazing period on winter pastures to increase land use while also maintaining or increasing stocking rates.
Their preliminary data from the western Dakotas indicate that using dormant season pastures briefly during early summer and winter with stocking rates to achieve 50 percent utilization of aboveground biomass is the preferred grazing strategy when compared to 30 or 50 percent winter utilization with no summer use.
This was a short term study, and responses depend on precipitation levels and environmental conditions.
Now, let’s return to the discussion of grass growth.
Grazing grasses earlier in the growing season, or early summer, may actually stimulate grass growth, by the same concept as when a lawn is mowed, if conditions for regrowth are present. By grazing to achieve a 50 percent utilization level during grass dormancy, this allows for litter to not build up and nutrients to be incorporated into the soil, potentially increasing soil health. These aspects can indeed contribute to herbage production potential.
However, one consideration is that this portion of the study was short term. It makes sense that this strategy allows for more grazing opportunities with little impacts to grasses on a short term basis. That being said, impacts to root health and growth were not documented and should be given consideration.
With this uncertainty, I would suggest not grazing the same pasture using the strategy of grazing early summer and again during the dormant season every single year. With any strategy that is incorporated into a grazing plan, continual evaluation of changes should be conducted and a vegetation monitoring program incorporated.
The study referenced in this article was from the following source: Nelson et al. 2006. Effects of dormant season grazing on herbage production and plant growth. Sheep & Beef DAY: 14.