Drought Effects on Diet and Weight Gains of Yearling Heifers in Northeastern Oregon

Abstract

Daily weight gains and diets of cattle were evaluated during a year with average precipitation and in a drought year on mountain range in northeastern Oregon. Forage intake was evaluated only in the drought year. Esophageally fistulated heifers were used to sample diet quality and botanical composition. Botanical composition of cattle diets was different (P<.05) in the late spring and early summer between years. When green grass and forbs were not available, browse was heavily utilized. Livestock weight gains and forage intake in the latter part of the grazing season were reduced (P<.05) during the drought year. This is attributed to depletion of browse, primarily common snowberry (Symphoricarpos albus). Diet crude protein and neutral detergent fiber concentrations were significantly (P<.05) correlated with average daily gains. When ruminants are consuming diets with more than one forage class, neutral detergent fiber and composition and yield of volatile fatty acids may more accurately evaluate the energy status of the diet than digestibility. Supplementation of crude protein could potentially improve average daily gains during drought years if browse was unavailable. Ranges with a high component of forbs and shrubs will ameliorate the negative effects of drought on average daily gains.