Written by Rachel Frost and Jeff Mosley, Montana State University
One important goal of grazing management is to prevent large numbers of animals from congregating in any one location for too long. Thus, grazing distribution is a major concern for livestock and land managers. This is especially important on sensitive areas such as streams and riparian areas. When grazing animals cause damage to soils or plants, it is often caused by poor animal distribution, not too many animals for the management unit. Animals clearly prefer some grazing sites over others, increasing the grazing pressure on used areas and leaving other areas underutilized. Spatial and temporal distribution of livestock is partly a function of rangeland resources, heterogeneity of vegetation types, forage abundance, and watering points. Water development, supplementary feed placement, and fencing are several tools that can help improve livestock distribution.
- Factors that Affect Livestock Grazing Distribution
- Managing Livestock Distribution
- Selective Culling
Animal behavior — Animals make conscious decisions about where to graze based on their perceptions of an area, their knowledge of plants consumed in the past, and their memory of potential choices.
Distance to water — Access to water is critical for grazing animals; therefore, the location and number of watering points are the main factors in determining movement, distribution, and concentration of grazing animals.
Topography — Hilly, mountainous, or rocky terrain can be difficult for grazing animals to traverse. The effect of topography varies with the kind of grazing animal.
Vegetation type — The distribution of grazing animals is strongly influenced by their forage preferences. Neighboring plant communities may receive different grazing pressure because they contain different kinds of plants or the plants differ in palatability.
Weather — Grazing animals must regulate body temperature and therefore seek out areas that provide thermal regulation such as shade or windbreaks.
Each management unit has its own unique set of distribution problems; however, several tools and strategies can be employed to draw animals away from preferred areas and into underutilized areas.
Water — Often the most effective way to improve the uniformity of grazing is to increase the number and/or change the location of watering points. Animals should not have to travel more than a quarter to a half mile from forage to water in steep, rough terrain or more than one mile on level or gently rolling ground. Animals will overuse sites near water locations rather than walk greater distances to abundant forage; therefore, the development of additional water sources can improve animal performance by making additional forage available.
Kind of livestock — The species and class of livestock grazed should be matched to the vegetation and the topography. Cattle prefer grasses and rarely use slopes over 10% when given a choice. Sheep utilize a variety of plants, while goats prefer shrubs and forbs. Sheep and goats are also more surefooted and agile, enabling them to use steeper and more rugged topography. The class (age and stage of reproduction) of grazing animals should also be considered. In some situation, yearling cattle may be more appropriate in rugged terrain than cows with calves as they are more agile and tend to travel farther. However, in other cases the opposite may be true, depending on range conditions and management goals.
Supplements — The number and location of supplements including salt, mineral, and feeds can be used to entice livestock away from overgrazed areas and onto underutilized ones. Protein and energy supplements are generally more effective in altering grazing distribution than salt alone. Supplements should be purposefully located away from water as animals tend to return to grazing following consumption rather than to water.
Fencing — The most direct way for managers to alter animal distribution is through fencing. Fences can subdivide large pastures into more manageable units or delineate areas requiring different grazing management strategies, including riparian areas or irrigated pastures. However, the expense of fencing, the need for additional water sources, and the subsequent impact on wildlife mobility should be considered before installing fencing. In general, fencing should be the "last resort" to solving animal distribution problems.
Improved grazing distribution can result in an increase in stocking rate because more of the available forage in a pasture is grazed and more forage is produced in formerly overused areas.
Herding is a proven tool for controlling cattle distribution, but herding is more effective when cattle behavior is considered. For example, trailing to a new pasture is made easier by identifying the leaders in a herd. Leaders are individual animals that consistently initiate movements that cause others to follow. Leaders tend to be the most popular cows, that is, cows that are the preferred associates of many herd members. Herd movements are easier when ranchers begin by locating the leader cows in the pasture and then purposely herding them first, before any others in the herd. This strategy enables other cows to notice movement by the leader cows, which encourages the rest of the herd to follow, more or less on their own.
Subgroups within a cattle herd should be dispersed as a unit. Otherwise, individuals separated from their subgroup will return to their former location. A herder should purposely relocate animals to alternative sites rather than merely harassing animals to disperse from a preferred site. Mere harassment often results in cattle returning within minutes or hours to their former site. Rather than trying to disperse large numbers of cattle at once, it is better to gather only one subgroup or a few subgroups at a time and then guide them to a new site. Upon arrival at the new site, the animals should be shown the location of water, salt or supplement, and palatable forage. The herder should then remain with the animals in their new location until the group has settled. This often requires half an hour to two hours. Cattle are considered settled when their heads are down grazing and cattle within the herd are pointed in different directions. The approach is similar to when trailing cow/calf pairs to a new pasture and then waiting there to make certain that every cow has claimed its calf. The time spent ensuring that subgroups establish their new home base saves much time that would otherwise be spent repeatedly harassing animals away from their former locations. Spending this time may markedly improve the intake of supplemental feed and its effectiveness in luring cattle into certain areas of a pasture. When moving cattle to a new grazing site, it is best to move them before they have watered; when relocating cattle to new loafing areas, it is best to move cattle soon after they have watered. These strategies make cattle more inclined to graze or rest when they reach their new location, rather than immediately returning to their former location.
Cattle distribution is influenced by where cattle enter a pasture because they tend to linger in the portion of a pasture first entered. This is especially true if the individual animals are unfamiliar with the pasture. Purposely having cattle enter pastures in successive years through different access points will encourage better distribution. Cattle that return to a pasture in successive years also tend to distribute themselves more completely across a pasture due to their familiarity with the topography, available forage, and the locations of water, salt, and supplement. When first released into a pasture, cattle should be moved in small groups to specific sites. Cattle should not be released at a boundary gate and left alone to find areas upon which to congregate because, once a foraging habit is developed, it is very difficult to disrupt by herding.
Individual animals sometimes do not respond to herding, and these animals should be culled from a herd. Eliminating uncooperative individuals will help develop a group of animals that readily responds to herding, and cattle can be trained to use certain areas of a landscape even though they may prefer to use others. There are examples where diligent herding has effectively trained cattle to spend less time within riparian areas. Most, if not all, of these herds at one time or another contained cows that did not respond well to the herding, and these cows were culled for this reason. In this way, selective culling has been used to lessen cattle use in riparian areas, but if the negative reinforcement from herding were to end, riparian use by these cattle herds would likely increase.
Some scientists and resource managers have suggested that selective culling also might be used to develop a herd of cattle that prefer to graze uplands. By watching where individual cows tend to graze and culling those that spend a lot of their grazing time in riparian areas, this strategy suggests that grazing pressure in riparian areas would, over time, be reduced.
Selective culling based on such observations should be considered cautiously because its effectiveness is uncertain. Although some cows do spend disproportionately more time within riparian areas, it is possible that in their absence and without diligent herding, the vacated riparian area would simply be re-occupied by other individuals in the herd.
This occurred when a selective culling strategy was assessed on foothill rangeland in southwestern Montana. A herd of 160 cows was grazing within a 1,563-hectare (3,862-acre) pasture from late July through September. Each autumn for four years, 10% of the cows were culled that spent the most time grazing in riparian areas during the previous late summer. All of the culled cows had spent at least 50% of their grazing time in riparian sites. After four years of selectively culling the riparian dwellers, the 160 cows in the herd spent 31% of their grazing time in riparian sites. Prior to selectively culling the riparian dwellers, the 160 cows in the herd had spent 30% of their grazing time in riparian sites.
The efficacy of selectively culling riparian dwellers may depend on the degree of home range overlap among individuals or subgroups. Little or no home range overlap provides less chance for other animals to perceive the absence of the culled animals and less chance that the vacated area will be reoccupied. Home range overlap is typically low in areas where resources are plentiful, such as areas with numerous watering sites and large amounts of nutritive, palatable forage, or where dense trees prevent cows from seeing each other across large distances. However, overlapping cattle home ranges are common on western rangelands where water, shelter, and desirable foraging sites are more limited. Consequently, selective culling is less likely to work in many rangeland environments. Even in the large foothill pasture in the selective culling study, for example, home range overlap was high among cows because they could readily see each other on distant ridges and most of the herd watered together at only two or three water sources.
Selectively culling riparian dwellers is less likely to be effective when ranchers introduce additional or replacement females that were not reared in the same pasture from which animals were selectively culled. This is because animals reared elsewhere cannot return to their natal home range and may occupy the home range vacated by selective culling. Finally, livestock managers using selective culling should also make certain that replacement females selected from the herd were not raised by riparian-dwelling cows. Otherwise, the replacements will likely perpetuate the foraging pattern of their culled mothers.