Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources


John C. Malechek


Grazing trials were conducted in west-central Utah in August and November, 1983. Sheep were stocked in 0.06 hectare paddocks containing a homogeneous stand of the shrub big sagebrush (Artemisia tridentata subsptridentata). Stocking rate was 1344 animal-unit-days per hectare. Close observation was made of plants and plant parts of the sagebrush that the sheep consumed or refused to consume. Similar samples were hand-harvested from browsed and rejected plants and plant parts. These samples were later analyzed in the laboratory for monoterpenoid content, crude protein levels and digestible organic matter.

There was large variability of monoterpenoid concentrations from plant to plant ranging from 0.06% to 0.63% dry matter basis among the browsed plants and from 0.30% to 1.80% among the rejected . Sheep consumed those plants and plant parts that were relatively lower in monoterpenoid content. They did not select for the proximate constituents (crude protein and digestible organic matter) of the whole

plant or plant parts. The rejected plants and plant parts were generally higher in bach monoterpenoids and proximate constituents than were the corresponding browsed plants and plant parts.

Seasonal effects were important on the composition of entire diets selected by the free grazing sheep. From observation, sheep consumed more sagebrush in autumn than they did in summer.

Samples collected from esophageally fistulated sheep showed crude protein content to be significantly (P = O.OS) higher in autumn than in summer. As sheep shifted the ir dietary select i on from annual grasses to big sagebrush , genera l ly upward trend in dietary crude protein was observed during both seasons . In vitro organic matter digestibilities (IVO MD ) were generally low due to the nature of plant parts consumed by the sheep, i.e., they consumed growth from the previous year.

Feeding station intervals (FSI) , the time spent per feeding station, were measured . A feeding station is the amount of forage available to a grazing animal when its forefeet are stationary. As sheep shifted their dietary selection to sagebrush, FSI increased significantly. Apparently shrubs offered relatively larger amounts of forage to select from than herbaceous vegetation call ing for more time per feeding station.



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