Nutritional value of antelope bitterbrush

Authors: Clements, Darin - Charlie; YOUNG, JAMES - Retired ARS Employee

Submitted to: The Progressive Rancher
Publication Type: Popular Publication
Publication Acceptance Date: 4/18/2023
Publication Date: 5/8/2023
Citation: Clements, D.D., Young, J.A. 2023. Nutritional value of antelope bitterbrush. The Progressive Rancher. 23(5):15-19.

Interpretive Summary:

Technical Abstract: Purshia species, such as antelope bitterbrush, are very important in the nutritional demand of mule deer, and to a lesser degree, domestic livestock. In order to appreciate the nutritional aspects of antelope bitterbrush, some understanding of the unique nutritional requirements of mule deer, the primary consumer of antelope bitterbrush browse is necessary. Analysis of forage samples are among the first scientific tests applied by resource managers attempting to better understand the role of forage plants in the ecology of western rangelands. Most analysis focused on grasses rather than shrubs since the objective was to better understand the forage requirements of domestic livestock rather than mule deer. By the late 1930s, wildlife ecologists were making serious attempts to better understand the nutritional requirements of mule deer. Wildlife ecologists, L. A. Stoddard and J. E Greeves reported on their attempt to conduct forage analysis of grasses shrubs and forbs on mule deer summer ranges in Utah. Noting that their forage analysis occurred on summer range habitat rather than mule deer winter ranges, they noted that antelope bitterbrush had a crude protein content of 15.4%, and therefor concluded that antelope bitterbrush is a highly reliable source of browse. Crude protein is often considered the most important dietary nutrient, as ungulates cannot survive without it. Even a slight deficiency adversely affects reproduction, lactation, and growth. Ruminants need protein in order for the rumen microorganisms to digest and metabolize carbohydrates and fats effectively. Ruminants, such as mule deer, must have access to adequate calcium and phosphorus. Calcium and phosphorus compounds form 90% of the mineral matter in the skeleton of most ruminants and about 75% of that in the entire body. On western rangelands, calcium supplies are usually ample in shrubs. Phosphorus is vital in many body processes including skeleton strength, intracellular fluids and compounds such as nucleoproteins and phospholipids. A deficiency in phosphorus or a high calcium to phosphorus ration may result in weak young (fawns), decreased lactation, failure to conceive and other abnormalities. Phosphorus is deficient in many shrub species on western rangelands during the winter months. Most ruminant nutrient intake goes towards maintaining its general metabolism. Browse species such as antelope bitterbrush, mountain mahogany and big sagebrush are good sources of energy, but as shrubs become older their nutritional value decreases as well. mule deer are not the only browsers that consume antelope bitterbrush. Bighorn sheep, elk, moose and pronghorn antelope also utilize the nutritional value that antelope bitterbrush provides. Montana Department of Fish, Wildlife and Parks reported, in research they funded, that antelope bitterbrush made up more than 50% of the mule deer diet. In their report they pointed out the significant increases in Elk populations and that antelope bitterbrush nutritional value was preferred by elk as well, resulting in habitat competition. Even though the elk diet was more diverse, major browse species that made up 95% of mule deer diets also made up 55% of elk diets. In southcentral Wyoming, antelope bitterbrush made up 80-90% of pronghorn and mule deer summer and fall diets, suggesting yet another sign of resource competition for antelope bitterbrush. Habitat changes over-time have resulted in a decrease in shrub communities, including antelope bitterbrush, which have resulted in former big sagebrush/bunchgrass communities being converted to annual grass dominance, cheatgrass, therefore increasing the chance, rate, spread and season of wildfires that in return threatens critical unburned browse communities. Also, many browse communities are becoming old and decadent and providing less nutritional value for wildlife, especially mule