INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 41 
SHEEP PRODUCTION ON RANGE PASTURES 
Changes in body weight of ewes kept in the 20 experimental range 
pastures were recorded during each grazing season from the winter of 
1937-38 to 1943-44. The sheep were weighed at the beginning of each 
grazing period—early, middle, and late winter—and at the end of the 
winter grazing season. ‘The number of ewes assigned to each range 
pasture was varied each year in order to achieve the desired intensity of 
grazing on the basis of the expected herbage production estimated in 
October. 
The sheep were allowed to graze freely without herding. They had 
access to snow or water every day. When snow was not readily avail- 
able, water was trucked to the ranges and placed in troughs. The 
sheep were bedded in different locations from time to time and the 
troughs were moved frequently to aid in obtaining uniform utilization 
within the range pastures. During cold weather it often was necessary 
to break and remove ice from the troughs so the sheep could drink. 
Average changes in body weight of ewes that were kept throughout 
the winter season on the range pastures are shown in figure 19 for the 
6-year period during which records were maintained. Ewes kept 
throughout the winter on lightly or moderately grazed range showed 
a net gain in each of the three winter grazing periods. The gains under 
moderate grazing in the first two periods exceeded those made on 
lightly grazed range. In the late winter period, ewes under light 
grazing gained slightly more than those under moderate. Total net 
gain for ewes under moderate grazing (11.4 pounds) was well above that 
for ewes under light grazing (8.5 pounds). Ewes in the heavily grazed 
pastures lost weight during the early and midwinter periods but gained 
about 2 pounds per head in the late winter period when early green 
growth of the forage plants became available. The gain during the 
late winter period under heavy grazing was less than half the gains 
made under light and moderate grazing, and was insufficient to offset 
earlier losses. 
The weights reported do not completely measure actual flesh con- 
dition of the animals. Ewes weighed at the end of the winter grazing 
season bear between 4 and 5 pounds more wool than at the beginning. 
Many of those a year or more old are carrying lambs which, together 
with fetal tissue and liquid, weigh 10 to 15 pounds by spring. Pregnant 
ewes that weigh the same in spring as they did when they reached 
winter ranges may therefore have lost 15 or 20 pounds in flesh when 
deductions are made for current wool growth and unborn lambs. 
Much wider variations in weight occurred in the late winter period than 
in the other two. This was probably because of differences in weight 
of fertile and barren ewes and differing stages of pregnancy of the 
fertile ewes. 
The kind and amount of forage produced on range areas influenced 
sheep weights considerably. Ewes in the lightly grazed range pastures 
10 and 11, where vegetation is primarily sand dropseed and shadscale 
with very small amounts of winterfat, showed approximately 2 to 3 
pounds less gain than those in other moderately or lightly grazed 
pastures. Sheep made the greatest gains on areas where wintertfat, 
Indian ricegrass, and bud sagebrush produced 30 percent or more of 
the forage. 
