Beef cattle forage conditioning of six northern Great Basin grasses: regrowth forage quality. Ganskopp, David^*,1, Aguilera, Lisa², ¹ USDA-ARS, Burns, OR, USA² College of Veterinary Medicine, Corvallis, OR, USA

ABSTRACT- Recent efforts to verify Anderson and Scherzinger's 1975 livestock forage conditioning hypothesis have generated mixed results. Our objective was to evaluate mid-summer and early-fall crude protein (CP) content of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. & Smith), Idaho fescue (Festuca idahoensis Elmer), bottlebrush squirreltail (Sitanion hystrix (Nutt.) Smith), Thurber's needlegrass (Stipa thurberiana Piper), basin wildrye (Elymus cinereus Scribn. A Merr), and crested wheatgrass (Agropyron desertorum (Fischer ex Link)Schultes) in ungrazed and grazed paddocks (stocked at vegetative, boot, and anthesis). In 1997, we obtained significant species x treatment and treatment x harvest date interactions. Except for Idaho fescue, CP of of regrowth from grasses grazed at anthesis was greater than grasses grazed during vegetative and late-boot treatments. With the exceptions of crested wheatgrass and basin wildrye, regrowth from vegetative and late-boot grazing was significantly higher in CP than ungrazed controls. Based on CP, bottlebrush squirreltail and Thurber's needlegrass responded with higher quality regrowth than basin wildrye, Idaho fescue, bluebunch wheatgrass, and crested wheatgrass. Ten of 18 grazed species/treatment combinations yielded regrowth exceeding 7.5% CP in 1997. Crude protein of all treatments typically declined by 1.5 to 2.5 percentage points between late-July and mid-September. Despite being a wetter year (110% vs 80% mean precipitation), no regrowth occurred among grasses grazed at anthesis in 1998. Grazing treatment, species, and harvest date main effects were significant with no interactions. Thurber's needlegrass, bottlebrush squirreltail, and Idaho fescue generated the highest quality regrowth (5.1%) of the 6 forages sampled, but no regrowth exceeded 7.5% CP in 1998.

KEY WORDS: crude protein , cattle grazing, yield, wildlife habitat