42 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE 
Weight changes throughout the winter grazing season were also 
influenced by the condition of the sheep when they reached the winter 
range. In years when summer and fall forage was inadequate and dry, 
many sheep arrived on the winter range in rather poor condition. 
These animals usually failed to improve much even on moderately 
grazed range. 
To determine the interrelated effects of grazing intensity on sheep 
condition from one winter period to another, a special study was made 
in 1940-41 and 1941-42. Fifty-four ewes of two age classes—27 three- 
year-olds and 27 four-year-olds—were carefully selected for uniformity 
of size and condition, at the beginning of the winter grazing season. 
These sheep were randomly assigned to 9 range pastures in such a way 
that one sheep from each age class was subjected to each of the 27 
possible grazing treatments involving the 3 winter grazing periods and 
3 grazing intensities. 
l2 
Bs HEAVY GRAZING 
10 
S RY MODERATE GRAZING 
8 : YOe, 
/ OY 
S | gL MA ticnut crazine iS Y 
© SM, 
== Kx 
= recon 
cer A SG 
my RS Y o ZY 
RX YO 
: ZF wees 
2 Sees eZ 
2 sess iG 
= Soces RX] 
Sees rene 
ly See KX 
S | 2 SZ ee 
: BY BR 
x SY, YG 
Se SZ SZ 
% 
» 
9 
~ 2 
EARLY MIDOLE LATE TOTAL 
WINTER WINTER WINTER 
Figure 19.—Average changes in body weight of ewes that grazed experimental range 
pastures throughout each grazing season at light, moderate, and heavy intensities, 
1938-39 to 1943-44, inclusive. 
These treatments are shown in figure 20. For example, 7 pairs were 
in lightly grazed pastures two or more periods, of which pair No. 1 was 
in lightly grazed pastures during all three winter periods; pair No. 2 
was in lightly grazed pastures in the early and middle periods and in 
moderately grazed pastures in the late winter; and pair No. 7 was in 
heavily grazed pastures in the early period and in the lightly grazed 
pastures in the other two periods. 
Averaged data for the light grazing treatment show that ewes gained 
a total of 8.4 pounds per head — 3.2, 1.4, and 3.8 pounds per head 
respectively for the early, middle, and late winter periods (fig. 20). 
The average total gain for moderate grazing was 13.0 pounds per head. 
