By: Roger Gates, Rangeland Management Specialist for SDSU Extension
Winter feed represents one of the largest costs for a livestock production enterprise. Grazing pasture that has been stockpiled for winter use is a rational alternative to limit costs resulting from both harvest (or purchase) and feeding of hay. Allocation of feed resources available from winter pasture is simplified to one degree because the quantity available can be determined at the beginning of the winter grazing period. Total feed available is entirely dependent on growing conditions during the preceding summer. No additional vegetation accumulation will follow a killing frost. Careful observation, supplemented with simple clipping can provide a very reliable estimate of the total feed available. Unlike grazing plans developed for the growing season, for which uncertainty is substantial because of rainfall variation, the uncertainty associated with winter grazing plans depends on snowfall. Winter grazing may be limited by the duration of open conditions which permit reliable grazing access. However, many producers, determined to make winter grazing part of a year-round grazing goal, have succeeded in providing grazing even when snow cover is substantial.
Exploiting Diet Selection
Conventionally, winter grazing involves turning livestock out in large pastures, anticipating the need to provide a protein supplement, particularly as the season advances and providing hay when snow cover interrupts or finally prevents access to grazing. This procedure may minimize labor and expense early in the winter, but it ignores the opportunity to exploit one of the principle tools available to the manager, animal diet selection. Grazing animals have an extraordinary ability to select a highly nutritious diet, even if average pasture quality is low. By selecting plants and parts of plants that are most palatable, both the energy and protein content of the diet can be considerably better than what the chemical analysis of a "representative" clipped pasture sample might suggest.
The challenge for the grazing manager is to optimally allocate those "most palatable" components available from the winter pasture. Allocating an entire pasture allows livestock to select a relatively high quality diet initially, but the opportunity to select a nutritious diet declines because, in the winter, there is no replacement of new and nutritious plant tissue as occurs during the growing season.
The alternative to providing the pasture "all at once," is to ration access gradually. More intensive winter grazing management, such as strip grazing, buffers the consumption of the most nutritious plants and plant parts, so that a more nutritious diet is available later into the winter. Once vegetation is stockpiled and "cured" at the end of the growing season, decline in nutritional value is limited. An opportunity for livestock to select a "better than average" diet can be preserved by using a rationing strategy. The greater opportunity livestock are given to select, the more nutritious a diet they can obtain. Managers control this through the total quantity of pasture which is accessible. In addition to extending the nutritional value of winter pasture, a rotational plan such as strip grazing can improve the utilization of the pasture through reductions in trampling and fouling. A rotation plan can be beneficial during the winter, just as it can be during the growing season. While there is no benefit from accumulated growth during a deferment, moving to a fresh pasture, even once or twice during the winter, better distributes grazing pressure across more plants and tends to maintain nutrient levels instead of a continuous decline which would occur without rotation.
Balancing Plant and Animal Needs
Decisions about winter grazing should consider at least two aspects, the nutritional needs of the livestock and stewardship of resources. Nutrient content of dormant forage is generally adequate, especially for the needs of a mature, dry cow. If the rationale for winter grazing is to limit costs, then expenditures for supplemental feed should be minimized. Protein is likely to be the first limiting nutrient in dormant pasture. Needs for supplementation will increase as nutrient demands increase, particularly for a pregnant female.
Testing the nutrient content of the vegetation selected by animals provides the best guidelines for determining supplementation needs. Another approach is using the NUTBAL procedure while cattle are grazing. Fecal samples are collected from the pasture and submitted through NRCS. Sample analysis, along with descriptions of the vegetation and the class and condition of cattle, provide guidance about the energy and protein adequacy of the diet being consumed.
Protecting the Resource
The "take half" rule of thumb is appropriate for winter grazing as much as during the growing season. Warm-season grasses, in particular, are susceptible to close grazing because substantial carbohydrate storage is located in above ground stem bases. Leaving sufficient cover to capture snow and protect the soil surface from exposure are critical. Late winter of early spring rains can be damaging rather than beneficial if the soil surface is left unprotected because of excessive winter defoliation.
Rotation to Maintain Dietary Protein
A capacity of ruminant livestock that can be exploited in winter grazing is their ability to recycle nitrogen. Dietary protein is essential for livestock, primarily to supply nitrogen. Optimal nitrogen concentrations in the rumen are necessary to maintain fiber digestion. Facilitating fiber digestion is critical to maintaining livestock performance on winter pasture because of the typically high fiber content of the diet. Research which has demonstrated adequate performance of beef cows when they receive supplemental protein every third day or even once a week demonstrates this capacity to recycle nitrogen and maintain adequate rumen concentrations. Grazing managers can take advantage of the same phenomena. Since animal selection results in the highest quality diet when access to "fresh" pasture is first provided, protein and therefore dietary nitrogen concentrations will be highest initially when a new strip is offered. Dietary quality may decline as the duration of occupation advances, but rumen nitrogen concentrations are likely to remain adequate. Providing a new strip every third day is probably sufficient to provide adequate nutrition for dry, pregnant mature beef cows.
Winter grazing requires prudent planning. Provision must be made for adequate water accessibility, protection from severe conditions and contingency for feed provision during blizzards or heavy snow cover. Nonetheless, grazing dormant pastures can provide attractive alternatives to reduce winter feed costs. While more intensive grazing management requires planning and time, this may be the year to consider it. It provides one way to make the low cost feed from pasture stretch as far as possible.