Graduate Thesis Or Dissertation
 

Conditioning of northern Great Basin grasses with livestock grazing

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  • Because forage quality of cool season grasses declines to sub-maintenance levels for ruminants late in the growing season in the northern Great Basin, there is a need to elevate protein levels and digestibility of grasses for both wild and domestic ruminants in late summer. Anderson and Scherzinger (1975) proposed using livestock forage conditioning early in the growing season to elevate forage quality of grasses for use later in the year. We tested their forage conditioning hypothesis among 6 grasses with cattle grazing applied at 3 stages in phenology (vegetative, boot, and anthesis) on the Northern Great Basin Experimental Range near Burns, Oregon. Forage quality of regrowth was compared among grazing treatments and with herbage from grasses rested throughout the growing season (ungrazed controls). Indices were: crude protein, in vitro dry matter digestibility, and yield sampled in late July and early September of 1997 and 1998. Grasses included: crested wheatgrass (Agropyron desertorum (Fischer ex Link) Schultes), bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith), bottlebrush squirreltail (Sitanion hysterix (Nutt.) J.G.Smith), Idaho fescue (Festuca idahoensis Elmer), Thurber needlegrass (Stipa thurberiana Piper), and basin wildrye (Elymus cinereus Scribn. & Merr). In both years,grasses showed the expected seasonal decline in forage quality (CP and IVDMD) as the season advanced. A positive response to conditioning occurred with crude protein of regrowth (x = 7.2 %) in 1997 with a treatment x species interaction (P< 0.003) and in 1998 (x = 4.6 %) with a significant treatment effect (P<0.001). In vitro dry matter digestibility of regrowth increased for boot and anthesis grazing treatments in 1997 (x = 50.4 %) (P<0.008), and for vegetative and boot grazing treatments in July samples of 1998 (x = 43.0 %) (P<0.007). Soil moisture content when grasses were grazed was a poor predictor of subsequent regrowth yields. In conclusion, forage-conditioning efforts appeared to be more successful in the drier of the 2 years. Bottlebrush squirreltail and Thurber needlegrass responded most favorably to forage conditioning treatments, while Idaho fescue and bluebunch wheatgrass exhibited the fewest favorable responses.
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