Submitted to: Western Regional Coordinating Committee #39
Publication Type: Abstract Only
Publication Acceptance Date: 5/2/2003
Publication Date: 6/2/2003
Citation: Taylor, J.B., Seefeldt, S.S. Effect of restricted access high density sheep grazing regimen on leafy spurge. Western Regional Coordinating Committee #39 Annual Reports. 2003. 2003:29. Interpretive Summary:
Technical Abstract: The objective of this experiment was to assess the impact of high density restricted versus free access grazing regimens on standing leafy spurge populations. A 0.6 hectare leafy spurge (spurge) infested area approximately 1.6 km East of Spencer, ID was divided into six 34 x 29 m main pastures. Three pastures remained open for free access (FA) grazing, and three pastures were further subdivided into four restricted access (RA) subpastures. Spurge total stem (TS) and damaged stem (DS) estimates, composition assessment, and biomass metering (capacitance) were conducted immediately prior to commencement of grazing, and DS estimate and biomass metering were again conducted in the morning every two days over an eight day grazing period. Thirty-six open ewes (age = 3 - 5 yr; body weight = 75.5 ± 7.3 kg; spurge experienced) were assigned, in groups of six, to each grazing regimen pasture. For FA regimen, ewes grazed freely for eight days, and for RA regimen, ewes grazed each subplot for two consecutive days and then were rotated (morning) to the next subplot. Stocking rate was approximately 61 ewes/ha/day. Prior to grazing, pasture plant composition, biomass, and spurge TS and DS estimates were similar (P > 0.60) for each grazing regimen (spurge = 45.6 ± 4.8%, grass = 40.0 ± 1.5%, other forb = 14.4 ± 4.4%; biomass = 1494.9 ± 129.8 kg/ha DM basis; spurge TS count = 194 ± 14/m2, spurge DS = 6.3 ± 1.1%). Total biomass disappeared in a linear (y = -79.255x + 1508.7; R2 = 0.38; P < 0.02) fashion and was not different between grazing regimens; approximately 42% of the pregrazed standing biomass was consumed at the conclusion of the grazing trial. Compared to RA, FA grazing regimen resulted in a higher (P = 0.05) percentage (55.3 vs. 39.2 ± 5.8%) of spurge DS on day eight. However, a linear (y = 4.07x + 6.1; R2 = 0.95; P < 0.01) increase in spurge DS was observed for RA as opposed to a quadratic (y = 1.07x2 - 2.64x + 6.89; R2 = .79; P < 0.02) increase for FA regimen. Overall, high density free access grazing regimen resulted in greater damage to the standing leafy spurge. However, early in the grazing period, the restricted access grazing regimen seems to induce a more rapid rate of leafy spurge damage.