36 CIRCULAR 8 04, U. S. DEPARTMENT OF AGRICULTURE 



of utilization, periodic weights of the sheep, and observations of their 

 grazing habits formed a basis for evaluating the three rates of stocking. 



Many combinations of soil and topography, each characterized by 

 certain range plant species, are found in the northern Great Plains. 

 Only four of the major situations were well represented on the experi- 

 mental range. The rolling areas of sandy clay loam soils are generally 

 occupied by blue grama, bluestem wheatgrass, other less important 

 grasses, a few herbs, and some big sagebrush. Rougher areas having 

 sandy to gravelly loam soils and characterized largely by bunch- 

 forming grasses make up a considerable part of the range. Bottom 

 areas are usually level or gently sloping, have heavy clay soils, and 

 are largely given to bluestem, buffalograss, and silver sagebrush. The 

 roughest portions are sometimes called badlands. The soil is heavy 

 and alkaline and the topography rough and broken. A variety of 

 browse species and a few hardy grasses and forbs compose a scanty 

 cover on these areas. 



Herbage production occurs largely during the main growing season, 

 April through September, coincident with about 70 percent of the 

 average annual rainfall. Spring growth begins generally in late 

 March or early April and is completed on the average by late July 

 or early August. During favorable years some additional herbage 

 may be produced in early fall by a few species that resume growth 

 following August or early September rains. 



Although the northern Great Plains range supports a wide variety 

 of native plants, most of the forage is provided by about 25 of the 

 most palatable species. The palatability and forage value of these 

 as well as other species varies with season of the year, stage of develop- 

 ment, and composition in the stand. On the experimental range all 

 species were most palatable when the plants were fresh and succulent 

 early in the growing season. Changes in forage value and palatability 

 during the grazing season affected its utilization by the sheep. 

 Greater utilization of the key species, blue grama, bluestem, and 

 threadleaf sedge, which resulted under heavy stocking as compared 

 to conservative and light stocking, was due to a higher percentage of 

 the total number of individual plants grazed rather than to lower 

 grazed stubble heights. 



The principal activities of the yearling ewes were grazing, bedding, 

 resting, and fighting insects. Grazing was accomplished largely 

 during daylight hours except in midsummer when insects and high 

 temperatures induced shading up. Under these conditions the year- 

 ling ewes frequently fed at night, alternating short periods of grazing 

 with frequent brief rest periods. During cool seasons and when 

 insects were not prevalent, the yearling ewes bedded throughout the 

 night, usually near a fence or other obstruction. Watering habits 

 were very irregular and salt was regularly used only when placed near 

 a watering place. When salt was placed away from water in an 

 attempt to aid distribution, the unherded sheep seldom found it. 



Natural factors such as wind and temperature affected the yearling 

 ewes. Their movements showed a strong relation to wind direction. 

 Both extremely high and low temperatures tended to restrict their 

 movements. The pasture fences affected the movements of yearling 

 ewes. This resulted in heavy grazing use near the fences and pro- 

 gressively lighter use at increasing distances from them. Predators 

 disrupted their activities and caused many actual losses in addition 

 to unmeasured losses in weight gain and general welfare. 



