Leafy spurge causes economic loss by reducing both herbage production and use. Herbage use by grazing cattle in various densities of leafy spurge (Euphorbia esulaL. #3EPHES) was evaluated over a 3-yr period in North Dakota. Forage production and disappearance were estimated in four density classes of leafy spurge. Use of cool- and warm-season graminoids, forbs, and leafy spurge was estimated during the middle and the end of each grazing season. Cattle used 20 and 2% of the herbage in the zero and low density infestations, respectively, by mid-season. Moderate and high density infestations were avoided until the milky latex in leafy spurge disappeared in early fall, and herbage availability in zero and low density infestations declined. Herbage use in moderate and high density infestations increased to an average of 46% by the end of the grazing season compared to 61% in zero and low density infestations. An annual herbage loss of at least 35% occurred in pasture infested with 50% density or more of leafy spurge.
We used six beef steers (377 +/- 12.7 kg) to evaluate the effect of advancing season on dietary composition, forage intake, and digestion. Six 10-d sample collections were conducted from mid-June to mid-December 1995. Diet quality data demonstrated a linear (P < .01) decline in CP and in vitro OM digestibility (IVOMD), whereas NDF, ADF, acid detergent-insoluble CP (ADICP; percentage of CP), and undegradable intake protein (UIP; percentage of CP) increased linearly (P < .01) with advancing season. Fecal output and ruminal OM fill (percentage of BW) demonstrated linear and cubic responses (P < .10) across the grazing season. Intake of OM (percentage of BW) followed quadratic and cubic (P < .10) patterns across season. Rate (percentage per hour) of in situ NDF disappearance (ISNDFD) decreased and lag time increased linearly (P < .01) with advancing season. Likewise, quadratic (P < .07) and cubic (P < .06) responses were observed for rate and lag time of ISNDFD. The rapidly degraded CP fraction increased (P < .10) linearly, and the rate of in situ CP disappearance (ISCPD) followed a linear and quadratic decrease (P < .10) with advancing season. In summary, these data indicate decreases (P < .10) in dietary CP, IVOMD, ISNDFD, and ISCPD with advancing season. In addition, seasonal increases (P < .10) in forage NDF, ADF, ADICP, UIP (percentage of DM) and fecal output were observed and correspond to the grazing of increasingly mature forage. These data suggest that mixed-grass range forage consumed by cattle in western North Dakota during November and December is deficient in degradable intake protein (DIP). Investigation of protein supplementation (particularly DIP) during these times is warranted.
Abstract:Flea beetles (Aphthona spp.) were introduced into leafy spurge (Euphorbia esula L.)-infested rangeland in east-central North Dakota. The study objectives were to evaluate the effects of the introduced insects on leafy spurge cover, density, and yield, and grass and grass-like yield of associated plant communities. Aphthona spp. were released in 1988 and 1989 at 2 sites near Valley City, N. D. Aboveground vegetative sampling for leafy spurge cover, density and yield, and grass and grass-like yield was conducted between 1993 and 1995. Belowground sampling of root density, dry weight and root buds was conducted between the release date and 1995. Aphthona spp. reduced aboveground cover, density and yield of leafy spurge and increased yield of grass and grass-like species. Leafy spurge root density, weight, and number of root buds decreased on insect release sites between release dates and 1995. Reduced stem density of leafy spurge and increased grass and grass-like yield, should enhance cattle use and production from these sites.
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