18 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE 
Utilization under heavy and light intensities shows the same general 
relation to herbage yields as that under moderate grazing. For ex- 
ample, under heavy grazing utilization of winterfat was 80 percent in 
pastures where it comprised only 10 percent of the total herbage and 
58 to 64 percent in areas where it made up 25 to 30 percent of the total — 
herbage. Under light grazing about the same relation existed between 
utilization and herbage yields, although the spread in utilization per- 
centage was not as pronounced as under moderate and heavy grazing. 
The utilization of highly palatable species, on ranges where they made 
up only a relatively small part of the total herbage, was often excessive 
before sheep would eat much of the herbage produced by less desirable 
plants. Because of the wide variations in utilization associated with 
the relative herbage production of the palatable forage species, it is 
necessary to govern the stocking rate not only on the presence of these 
species, but also on the relative yields of the species within the plant 
cover. On depleted ranges where desirable forage species constitute 
an extremely small proportion of the herbage, stocking rates must 
necessarily be low enough to permit these scarce species to increase. 
INFLUENCE OF GRAZING INTENSITY 
On the experimental range pastures three degrees of grazing—light, 
moderate, and heavy—were applied. The plan was to maintain fairly 
uniform utilization of the herbage produced the previous summer by 
three key forage species. Planned utilization by weight under mod- 
erate grazing was 75 percent for Indian ricegrass and 50 percent for 
winterfat and bud sagebrush. 
The desired intensity of grazing for the various range pastures waS 
obtained and controlled reasonably well by varying the stocking each 
year on the basis of October herbage estimates. The moderately 
grazed pastures were stocked at an average rate of approximately 14 
sheep-days per acre. Pastures designated as heavily grazed had about 
25 percent heavier stocking (17 sheep-days per acre) and those lightly 
grazed 30 percent lighter (10 sheep-days per acre) than those grazed at 
moderate intensity. 
The average yearly percentages of utilization of the herbage of the 
major forage species, obtained under the three intensities of grazing 
for the period 1935-46, are given in table 5. Utilization of the various 
species under light and heavy grazing was not uniformly 25 percent 
higher or 30 percent lower than that obtained under moderate grazing 
as might have been assumed would be the case under the plan of 
stocking. Utilization of winterfat under moderate grazing, for ex- 
ample, was only slightly above that under light grazing. However, 
in heavily stocked pastures sheep ate 11 percent more of the winterfat 
herbage than in moderately stocked pastures. This represented ap- 
proximately 20 percent greater use. There was a similar spread in 
the utilization of Indian ricegrass between the three intensities of 
grazing. With light stocking sheep ate only small amounts of galleta 
and sand dropseed, 25 and 9 percent of the herbage, respectively. As 
the grazing intensity increased they consumed more and more of these 
species. Under heavy grazing, utilization of galleta herbage was 67 
percent and sand dropseed 40 percent. 
