12.10: Grazing

We have mostly discussed using manure from livestock that are confined in lots or barns and have forage brought in from fields. Pastures allow animals to graze their own feed and are most appropriate for ruminant animals (cattle, sheep, goats, etc.) that can digest forage crops. Nonruminant animals like chickens and pigs can also be raised on pastures, but they derive little feed from the field and need to be supplied additional feeds such as grains. The benefits are then mostly for animal welfare and health, and perceived improved food quality rather than optimum feed and nutrient management, which many consumers are willing to pay for.

Figure 12.3. Rotational grazing system for dairy cows with relatively high stocking densities for short durations. (White lines in the background are paddock separation wires.)

For years animals were grazed in large areas, out on rangeland or on farms, where they might be switched between two pastures during the grazing season. Dairy farmers commonly used one or two “night pastures” with cows turned out after the evening milking. But these continually grazed 0r very infrequently rotated pastures produced poorly as animals ate the regrowth again and again, weakening plants. Plants need to grow to a reasonable size before root reserves can be fully replenished, and continually regrazing early shoot regrowth depletes root reserves, making it harder for the plant to regrow again after grazing. But using what’s sometimes called management intensive grazing (MIG), in which animals are rotated through many pastures and do not re-graze a paddock until plants have sufficiently regrown, has shown great improvement in pasture productivity and animal health. Depending on the season and weather, the rotation cycle can be as short as a week or 10 days and as long as 6–8 weeks. For dairy farms using MIG, cows are turned out to a fresh paddock after each milking (Figure 12.3). Other animals might be moved to a new pasture daily or every few days.

A well-managed grazing system has inherent efficiencies because the harvesting and fertilization require no (or limited) equipment and human labor. It is also attractive to those who are concerned with animal welfare, as it is more in line with the natural living environment for most farm animals. A common counterargument is that animals on pastures expend more energy on foraging compared to confined animals (reducing meat or milk yields) and that the most productive biomass crops, like corn and sorghum, don’t lend themselves well to grazing. But in most cases cows grazing on high-quality, intensively managed pastures result in a lower cost of production once you factor in lower labor and machinery needs for such tasks as cleaning barns, spreading manure, harvesting crops, transporting animals to barns and feeding them out. The use of the newer styles of fencing and electric fence chargers make it easy to quickly set up new grazing paddocks, and once dairy or beef cows are trained to electric fences, a single-strand electric internal fence is enough to contain them in the paddock.

Figure 12.4. Grazing allows for productive use of marginal lands (New Zealand).

Grazing, especially involving small ruminants like sheep and goats that can handle rough terrain, permits productive use of marginal lands that generally aren’t suitable for intensive crop production. In fact, much of the hillsides of the northeastern United States were pastures stocked with sheep during the 1800s, but due to a shift in agricultural and labor markets were then reforested. But in other countries hillsides are still productively managed as pastures (Figure 12.4).

Well-managed pastures promote good soil health because they combine three beneficial practices: perennial forage crops, absence of tillage and regular manure additions. A soil health study involving a wide range of New York cropping systems confirmed that pasture fields had far better scores than other cropping systems for soil organic matter content, active carbon, protein, respiration, available water capacity and aggregate stability.

Other grazing systems. In addition to management intensive grazing of permanent pastures, there are other grazing systems. Sometimes intensive grazing is taken to an extreme level through mob grazing, where extremely high stocking densities (100,000 pounds of animals per acre) are used for very short time periods (8–12 hours). This approach is used as a soil amelioration technique, where animals suppress or kill poor quality plant species and with their hoofs help to reseed the paddock with more productive species. In some situations animals are allowed to roam over larger rangeland areas but are stocked densely during the night time. The carbon, nutrients and seeds gathered during the day are excreted into the smaller area and provide a significant boost for soil fertility and revegetation (as discussed with “plaggen soils” in Chapter 7). In general, however, pastures need to be managed with careful consideration of the biomass production potential of the land, which is typically defined by rainfall, temperature and soil quality. Overgrazing happens when farmers maintain excessive herd sizes, often based on normal or good growing conditions, during years that experience low rainfall. This causes excessive foraging, weakening or die-off of the pasture plants, and subsequently, soil degradation and further loss of productivity.

Farmers using management intensive grazing normally only sell animal products, not crops. Integrated crop-livestock systems, in which both crops and animal products are sold commercially, are increasingly used in drier regions of traditional grassland like the North American Great Plains. Several systems exist and may all be used on the same farm:

• Grazing annual crop residue works with an annual row crop system where the grain is harvested and the residues are grazed during the dormant periods in the autumn, winter or dry season. Although this does not meet annual feed needs, it reduces feed costs and improves nutrient and carbon cycling. Cattle grazing of corn residue in winter is common in the Great Plains and has been shown to increase soil health and crop yields. In some cases, farmers also leave some of the grain unharvested (corn or sunflowers, for example), enabling forage access for the grazing animals during the winter, even with deep snow.
• Swath grazing involves annual crops such as barley and triticale, cut in the autumn. They are left in swaths (heaped rows) for grazing, mostly for beef cattle (Figure 12.5). The grazing is typically controlled through temporary fencing. Swath grazing improves forage accessibility, especially when there is deep snow, by concentrating and stacking the forage into narrow swaths.
• Grazing annual forages involves livestock grazing on annual or short-season crops, which can also function as cover crops. Cool-season crops (winter wheat, rye or triticale) can be planted in the fall for spring grazing, or planted in the spring (oats, barley, wheat) for late-spring and early summer grazing. Brassicas like turnips, kale and legumes like forage peas are often mixed in. Warm-season annual grasses like sorghum, sorghum-sudangrass and millet can be planted in late spring to provide autumn grazing. These systems can be matched with cash crops after grazing, like the field in Figure 12.6. (This picture was taken in the month of April.) Controlled grazing of cover crops can significantly contribute to high-quality forage and can be used as a means to terminate a cover crop.
• Grazing perennial forage crops that are part of a crop rotation on integrated crop-livestock farms involves raising forages, usually for two to 10 years, that can be either hayed or grazed. One of the great advantages of integrated crop-livestock farms is that they provide a very good reason for growing perennial forages, which considerably enhance soil health.

Full reliance on pastures to provide all the animals’ forage needs is generally not feasible, even with ruminants. Invariably pastures experience periods of limited growth during dry or cold seasons, and additional feed is needed. Sometimes pastures are “stockpiled” (that is, left ungrazed or not hayed) for use when crops aren’t growing. In many cases baled hay has to be supplied from other sources. Most animals also require additional grains for optimum growth. Emergency feed may be required during unusual weather events like drought, high snow or ice.

Figure 12.5. Swath grazing of winter forage in the northern Great Plains. Photo by West-Central Forage Association.

Figure 12.6. Mixed winter cover crop used for grazing (Washington State). Photo by Bill Wavrin.