INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 47 
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FraurE 21.—Sheep grazing black sagebrush in an experimental allotment during the 
early winter. The tall, nutritious forage plants in this allotment enabled ewes to 
maintain themselves in good condition throughout most winters. 
of low quality. Asa result the sheep gained an average of 3 pounds 
less than those on the moderately grazed range. Differences in condi- 
tion of the sheep in the two herds, when they reached winter range in 
the fall, may also have influenced the weight gains. 
Average weight changes in sheep by age class for the period of study 
are shown in table 13. Sheep in each of the age classes were fairly 
comparable as indicated by fall weights. The most actively growing 
class, those under 1 year, naturally made the greatest gains in weight. 
Gains for this class under moderate grazing, however, were twice as 
great as under heavy grazing. Breeding ewes (those 1 year old or 
older) on moderately grazed range gained approximately 9 pounds per 
head, whereas those on heavily grazed range made a gain of only 0.4 
pound or one-twentieth as much. Under heavy grazing ewes 6 years 
old or older showed a net loss of 0.5 pound in body weight. In severe 
winters the greatest loss occurs in ewes over 6 years of age and in the 
young sheep less than 1 year old. ‘The old ewes on heavily grazed 
range lose weight rapidly, especially in cold weather, and become poor 
and weak. 
Trends of weight changes of the sample ewes in herds A and B during 
the grazing seasons of 1937-38 and 1938-39 are shown in figure 22. In 
these years weights were recorded at several intervals throughout the 
winter. Weather in the winter of 1937-38 was rather severe and 
grazing was difficult for both herds. During part of the winter of 
1938-39 weather conditions were likewise severe. In spite of this 
the sheep remained in good condition because they had access to the 
excellent forage crop that was produced the previous summer. In both 
years, however, ewes on moderately grazed range showed net gains in 
weight at the end of the season, whereas those on heavily grazed range 
lost weight rapidly during the midwinter period and failed to gain 
enough in the late winter to offset the loss. 
