Grazing Patterns of Cattle
Dr.Mario A. Villarino, County Extension Agent for Agriculture and Natural Resources
A recent publication from Texas A&M Agrilife Extension titled Estimating Grazeable Acreage for Cattle By Jason C. Hohlt, Robert K. Lyons, C. Wayne Hanselka and David McKown has the report of research using cattle fitted with Global Positioning System (GPS) collars shed light on how cattle behave in response to different features of the landscape. “The research was conducted on ranches in different regions of Texas to demonstrate the influence of landscape features such as brush density, rock cover, surface slope, water and forage species on livestock grazing. Test sites were in the Davis Mountains, Edwards Plateau and South Texas Plains. Digital aerial photographs of the test ranches and overlays showing the various ecological sites within each photograph were obtained. An ecological site is an area of land with specific physical characteristics that differs from other kinds of land in the types and amounts of vegetation it produces. Descriptions of these ecological sites define certain landscape features. For example, an ecological site designated as gravelly redland has 36 percent or less surface rock cover. The ecological site maps and aerial photographs enabled researchers to predict which areas cattle would not use because of their apparent brush and rock cover, slope, or inaccessibility. (Landowners can contact a local USDA Natural Resources Conservation Service office for help acquiring digital aerial photographs and ecological site overlays for their property.) Next, areas that appeared ungrazeable from the maps were observed on the ground. Observers measured brush density and rock cover and determined the herbaceous plant species growing in each area. Again, researchers predicted grazeability from their ground observations. To test the map and ground observation prediction methods, researchers fitted cattle with GPS collars and recorded their positions for 23 days.
Collars were programmed to take a position fix every 5 minutes and are accurate to within 10 to 16 feet of the true location. Both map estimates and ground estimates were fairly accurate, as validated by the actual GPS locations of cattle on the ranches. However, ground observation is clearly the more accurate method for predicting the grazeability of an area. While aerial photographs can give a general estimate of the brush cover on your property, they do have limitations. If photographs are taken at the time of year when brush plants such as mesquite have dropped their leaves, the extent of brush cover may not be apparent. Photographs are helpful in pinpointing areas that might be too brushy for cattle so that these areas can be checked on the ground. There is often more brush in the pasture than can be seen on an aerial photograph.Actual brush density should be checked and scored in several areas on the property. Walk a straight line through each area and assign a brush density score every 20 steps. Use Figure 1 as a guide in determining brush density scores. The GPS collar research showed that, overall, only 25 percent of areas with a brush density score of 3 were visited by cattle, and that cattle completely avoided areas with scores of 4 or 5 .This relationship was true in both the Edwards Plateau and South Texas Plains, regions with very different brush species. The GPS collar study showed that cattle tend to avoid areas with 30 percent or more rock cover. When determining a rock cover percentage, remember that if an area is uncomfortable for a person to walk on, it will also be uncomfortable for cattle. Percent slope is calculated as the change in elevation over a 100-foot distance. Cattle prefer flat areas or broad, gentle slopes and are usually deterred by steep slopes. In the GPS collar study at the Davis Mountains site, 95 percent of cow locations were on slopes of 11 percent or less.
The distance cattle have to travel to find water affects their use of a pasture. In general, cattle graze within about 1 mile of water, as was shown in the Davis Mountains study where about 73 percent of cow locations were within a 1-mile radius of either of the two water sources available. Another consideration when determining grazeable acreage is what cattle will and will not eat. So you will need to be able to identify some of the major plant species, especially grasses. Grasses such as threeawn (Aristida spp.), red grama (Bouteloua trifida) and Texas grama (Bouteloua rigidiseta) are very unpalatable to cattle. Cattle will avoid areas dominated by these species if more palatable grasses are available elsewhere. Likewise, cattle will not use areas with heavy concentrations of certain perennial weeds such as goldenweed (Isocoma drummondii) and wolfweed (Leucosyris spinosa). The frequency of herbaceous species was estimated at the South Texas Plains locations. No dominant grasses emerged as attractants or deterrents in grazed or ungrazed areas. However, at two of these locations the average number of herbaceous species was greater in the grazed areas Although there was little difference in the number of herbaceous species within the grazed and ungrazed areas at site 1, the grazed areas did have less Kleberg bluestem, a relatively unpalatable grass. It may be that cattle avoid this grass when possible. Some areas of pastures may have low brush density scores, little rock cover, adequate water, gentle slopes and palatable forage species, but still not be grazed because they are inaccessible. These areas may be surrounded by dense brush, heavy rock cover and/or steep slopes. Aerial photographs with ecological site layers and descriptions can be very helpful in identifying such areas. If possible, creating roads or trails into these areas will make them more accessible to cattle“. For more information on this or any other agricultural topic or to request the complete publication report, please contact the Hopkins County Extension Office at 903-885-3443 or e-mail me at mavillarino@ag.tamu.edu.
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