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Title: Targeted grazing of white locoweed: Short-term effects of herbivory regime on vegetation and sheep

Author
item GOODMAN, LAURA - New Mexico State University
item CIBILS, ANDRES - New Mexico State University
item LOPEZ, STEPHANIE - New Mexico State University
item STEINER, ROBERT - New Mexico State University
item GRAHAM, JOHN - New Mexico Extension Service
item MCDANIEL, KIRK - New Mexico State University
item ABBOTT, LAURIE - New Mexico State University
item Stegelmeier, Bryan
item HALLFORD, DENNIS - New Mexico State University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2014
Publication Date: 11/1/2014
Publication URL: http://handle.nal.usda.gov/10113/62982
Citation: Goodman, L.E., Cibils, A.F., Lopez, S.C., Steiner, R.L., Graham, J.D., Mcdaniel, K.C., Abbott, L.B., Stegelmeier, B.L., Hallford, D.M. 2014. Targeted grazing of white locoweed: Short-term effects of herbivory regime on vegetation and sheep. Rangeland Ecology and Management. 67(6):680-92.

Interpretive Summary: This is a study to compare determine if two year targeting grazing of white locoweed in New Mexico causes changes in plant populations and seed banks or what the effects of intermittent or short term feeding might have on sheep. Grazed plots were compared with control plots and those treated with herbicide (picloram plus 2, 4-D: HER). White locoweed seed density in the soil seed bank was not reduced with grazing and non-target vegetation was mostly unaffected by treatments. Grass canopy cover increased in grazed and herbicide plots throughout the study. Percent bare ground was unchanged in grazed plots but decreased (P = 0.03) in HER plots. After 24 days, ewes in the intermittent grazing treatment had lower levels of serum ALKP (P < 0.01), and AST (P = 0.02), and marginally lower swainsonine levels (P < 0.07) than the short term grazing ewes that tended to exhibit lower serum T3 (P < 0.07) and similar serum T4 (P = 0.25) levels. Time spent feeding tended to differ (P = 0.06) between treatments. Body weight gain was the same (P = 0.19) regardless of treatment. This suggest that intermittent grazing of locoweed-infested rangeland with sheep may be a viable short-term means of reducing locoweed density without detrimentally affecting animal health.

Technical Abstract: White locoweed (Oxytropis sericea Nuttall) and non-target vegetation response to two years of targeted grazing by sheep, one treatment of picloram plus 2, 4-D (HER) or no treatment (CON) were compared. Serum of sheep that grazed locoweed intermittently (IGZ, five days on locoweed followed by three days off locoweed) versus counterparts that grazed locoweed continuously for 24 days (CGZ) was also examined. Alkaloid toxicity was inferred by serum levels of thyroxine (T4), triiodothyronine (T3), alkaline phosphatase (ALKP), aspartate aminotransferase (AST), and swainsonine, as well as behavior and body weight gains. Three sites were used in a randomized complete block design. IGZ, CGZ, and HER treatments reduced locoweed density (P < 0.01), canopy cover (P < 0.01), number of flower stalks (IGZ: P = 0.02, CGZ and HER: P = 0.01), and plant size (P < 0.01). White locoweed seed density in the soil seed bank was not reduced with grazing and non-target vegetation was mostly unaffected by treatments. Grass canopy cover increased in grazed and herbicide plots throughout the study (IGZ: P = 0.03, CGZ and HER: P < 0.01). Percent bare ground was unchanged (IGZ: P = 0.46, CGZ: P = 0.44) in grazed plots but decreased (P = 0.03) in HER plots. After 24 days, ewes in the IGZ treatment had lower levels of serum ALKP (P < 0.01), and AST (P = 0.02), and marginally lower swainsonine levels (P < 0.07) than CGZ ewes that tended to exhibit lower serum T3 (P < 0.07) and similar serum T4 (P = 0.25) levels. Time spent feeding tended to differ (P = 0.06) between treatments. Body weight gain was the same (P = 0.19) regardless of treatment. IGZ of locoweed-infested rangeland with sheep may be a viable short-term means of reducing locoweed density without detrimentally affecting animal health.