Ruminants, because of their unique ability to convert forages and byproducts into high quality and nutrient dense foods for human consumption, are expected to fill increasingly significant and sustainable roles in meeting increasing world food demands. In ruminants, a high amount of metabolizable energy use (>50%) goes to maintain parent populations and over 70% of whole-herd energy expenditure in beef cattle can be associated with maintenance. Identifying and quantifying processes that consume energy associated with maintenance and productive functions create opportunities to enhance livestock management and food production. Our current understanding of animal energetics is built on relationships between metabolizable, retained, and heat energy (ME, RE, and HE, respectively; where ME = RE + HE). In extensive grazing systems, beef cattle are subject to environmental extremes that increase energetic requirements. Existing equations for estimating NEm for physical activity of grazing are likely better suited for cows during their acclimation to the grazing environment and do not accurately predict observed outcomes in cattle acclimated to extensive grazing conditions. Estimates of NEm expenditure for grazing activities of mature well-adapted cows appear substantially less than predicted by traditionally used equations. Impacts of climate on grazing energetics are associated with seasonal changes and temperature extremes. However, currently available equations do not accurately account for how animals modify their behavior to mitigate impacts of temperature extremes. Recent work suggests that cattle behavior, including positioning relative to slope, solar radiation, and wind can substantially reduce energy expenditure associated with cold extremes. Additional research is needed to more clearly define the impacts of physical activity and environmental extremes, particularly in extensive grazing situations. Data in this regard should provide a platform for more efficient beef cattle production and, consequently, contribute to meeting increasing world food demands.

Livestock grazing can affect habitat quality for grasshoppers through effects on food and oviposition site availability, microclimate, and other factors. Because of this, some authors have suggested that grazing programs can be used to help manage pest grasshopper populations. In a 6-yr study, we controlled access of cattle to replicated experimental plots on an Agropyron spicatum/Poa sandbergii pasture to create consistent year-to-year differences in postgrazing plant cover, with resultant affects on microclimate. After sampling grasshoppers multiple times after grazing treatments each summer, we found evidence of between-treatment differences in grasshopper abundance for the entire assemblage during 4 of the 6 yr. Some species, including Melanoplus sanguinipes (perhaps the worse rangeland grasshopper pest in the western United States), tended to be more abundant on ungrazed plots, whereas Melanoplus gladstoni often had greater densities on heavily-grazed plots. The effect of grazing on grasshopper densities in this study was lower in magnitude and less consistent among years than in a study we conducted simultaneously at a nearby site where the vegetation was dominated by the exotic species crested wheatgrass (Agropyron cristatum). Our results generally support proposals that grazing could be used to reduce pest grasshopper densities, although the effectiveness of a particular grazing scheme may vary among sites, years, and grasshopper and vegetation assemblages.

The invasive plant species, Spotted knapweed (Centaurea maculosa Lam.) and common tansy (Tanacetum vulgare L.), are altering native rangeland communities in western North America (Tyser and Key, 1988; Jacobs, 2008). To increase our understanding of why sheep consume these species to a certain extent and cattle avoid them, in vitro dry matter digestibility (IVDMD), microbial gas production (MGP), and microbial purine concentrations (MPC) of C. maculosa or T. vulgare leaves or stems incubated in sheep or cattle rumen fluid were measured. Rumen microbes were not conditioned to these plants in Trials 1a and 1b, but were conditioned in Trials 2a and 2b. Total MGP of C. maculosa leaves or stems (Trial 1a; P 0.10). Conversely, conditioning ewe rumen microbes to T. vulgare increased (Trial 2b; P < 0.04) IVDMD of A. arundinaceus hay and T. vulgare leaves or stems. Centaurea maculosa leaves and stems and T. vulgare leaves were used by rumen microbes as a nutritious feedstuff and nutrient characteristics and overall low IVDMD and MPC suggest that T. vulgare stems represent a poor quality forage. To increase consumption, further research is warranted to determine species composition and physiological differences between sheepand cattle-adapted rumen microbes.

Spotted knapweed (Centaurea biebersteinii DC.) is a perennial, invasive forb that infests millions of hectares of private and public rangelands in western North America. Previous research indicates that domestic sheep (Ovis aries) readily graze spotted knapweed, but landscape-scale prescriptive grazing of spotted knapweed has not been studied. We quantified the diets and forage utilization of a ewe-lamb band (about 800 ewes and 1120 lambs) that prescriptively grazed spotted knapweed-infested foothill rangeland in western Montana in the summers of 2003 and 2004. In mid-June or mid-July, sheep grazed light and moderate infestations of spotted knapweed (13% and 36% of vegetative composition, respectively). Nutritive quality of sheep diets was similar to sheep grazing uninfested rangeland, and sheep exhibited few forage preferences or avoidances. Sheep diets averaged 64% spotted knapweed in the moderate infestation and 26% in the light infestation. Sheep in the light infestation ate fewer graminoids in June than July (17% vs. 55% of their diet, respectively; P = 0.04), whereas sheep in the moderate infestation ate fewer graminoids in July (45% in June vs. 20% in July; P = 0.09). In the moderate infestation, relative utilization of spotted knapweed was greater in July than June (50% vs. 35%, respectively; P = 0.04), but averaged 46% in the light infestation. Previous research suggests that these levels of relative utilization may make herbicide application uneconomical. Relative utilization of graminoids was light in both infestations (15% in June or 31% in July). Our results indicate that sheep can prescriptively graze light or moderate spotted knapweed infestations in either June or July. Sheep consumption and relative utilization of graminoids will be less if light infestations are grazed in June rather than July. In moderate infestations, sheep will eat fewer graminoids and utilize spotted knapweed more heavily when grazed in July rather than June.

Miridae of the genera Labops and Irbisia, collectively referred to as "black grass bugs," can cause significant damage to wheatgrasses (Poaceae) of several genera on western North American rangeland. Another mirid in the same area, Capsus cinctus (Kolenati), causes damage to bluegrass (Poa spp.). Previous studies suggest that grazing management may reduce mirid populations on rangeland by eliminating preferred oviposition sites and reducing accumulations of litter that provide diurnal refuges for nymphs. We tested the hypothesis that grazing reduces mirid populations, along with those of Reduviidae, during a controlled grazing experiment. Densities of mirids and reduviids declined with increasing intensity of grazing, even though grazing occurred after the peak of mirid abundance each year. This suggests that declines in hemipteran densities resulted from grazing that occurred during previous years, perhaps because the most heavily grazed plots had the least plant litter. The results further confirm that grazing has the potential to control black grass bug populations, although the benefits could be potentially offset by negative impacts on beneficial insects such as reduviids.

The spread of the invasive, Eurasian spotted knapweed (Centaurea maculosa Lam.) across the northwestern United States would be reduced if livestock regularly consumed it. We determined if white-face yearling ewes (n = 36) conditioned for 12 days to fresh-cut spotted knapweed, with or without molasses, would increase their use of it during a 5-day field trial and/or a 4-day drylot trial. Ewes were assigned to one of three treatments: ewes not conditioned to spotted knapweed or molasses (NC), ewes conditioned to spotted knapweed (SK), or ewes conditioned to spotted knapweed sprayed with liquid beet molasses (SKM). During conditioning, all groups consumed high amounts of their feed. Nonconditioned ewes (NC) consumed less than ewes conditioned to spotted knapweed (SK, SKM), indicating spotted knapweed did not inhibit initial consumption. In the field, SKM ewes spent more time grazing spotted knapweed and other forbs than SK ewes. In a drylot, time spent eating and intake of spotted knapweed and bromegrass (Bromus inermis Leyss.) varied through time. Conditioning yearling ewes to spotted knapweed, with or without molasses, did not increase consumption of this invasive plant, possibly because sheep inherently graze spotted knapweed only to a certain extent, or we did not use enough spotted knapweed during conditioning.

1. Metabolic demands of cattle grazing winter range may be over-predicted by models that do not account for animal behavior. Cattle may conserve energy and mitigate cold stress by short-term behavioral responses.2. We solved the thermal balance equation for a revolving three-dimensional model using advanced thermal solution software to simulate unconstrained cattle during winter. This software, developed for inanimate objects, predicted energetic requirements within expected range of values.3. Solar radiation and apparent surface area were instrumental in reducing energy requirements, especially on cold clear days, whereas wind velocity and ambient temperature had a lesser effect on well-insulated cows in good body condition. (c) 2007 Elsevier Ltd. All rights reserved.

• Most broadleaf weeds were brought from Eurasia to North America, where they are spreading rapidly across public and private land. • Millions of dollars spent on herbicides and biological control address only the symptoms of the spread, not the cause. • These weeds can be highly nutritious, and many are readily grazed by livestock during the growing seasons. • The age and breed of livestock best used to tackle herbaceous weeds will depend on the grazing situation. • Broadleaf weeds are most susceptible to grazing damage when they are initiating flower production and rapidly elevating flower stalks. • The number of days to graze in a year depends on the target broadleaf weed and the surrounding vegetation. • Broadleaf plants are generally most nutritious during their rapid growth phase when high water and nutrient uptake facilitates cell expansion. • Secondary compounds in broadleaf weeds may reduce palatability by causing negative digestive consequences. • The period of highest nutritional need for ewes and nannies generally coincides with the time of highest forage value in the weeds. • Biological control and targeted grazing may be combined for an enhanced effect in controlling broadleaf weeds.

Spotted knapweed (Centaurea maculosa Lam.), an introduced perennial plant, has invaded large areas of rangeland in the northwestern United States. Grazing animals may disseminate the weed by transporting seeds in their digestive system and depositing them in their feces. In this study percent viability and emergence of spotted knapweed seeds that passed through mule deer (Odocoileus hemionus hemionus) and sheep (Ovis aries) were determined. Percent viability included seeds that germinated and seeds that tested positive with tetrazolium. In the first trial, we pulse dosed 3 mule deer and 4 ewes with 5,000 spotted knapweed seeds each. Seed recovered from manure collected daily for 10 days after dosing was tested for percent viability. We recovered 11% of the knapweed seeds from the 3 mule deer, and 4% from the sheep. Based on high variability in (0 to 26%) percent viability of recovered seed, we thought that our drying the manure at 50 degrees C may have killed some of the spotted knapweed embryos. To determine if drying at 50 degrees C affected viability, we pulse dosed 4 rams with 5,000 spotted knapweed seeds each in a second trial. One subsample of manure was washed the same day to recover seeds and then dried at 35 degrees C, a second subsample was dried at 50 degrees C, washed, and then dried at 35 degrees C. We recovered 17% of the spotted knapweed seeds from the 4 rams. No viable seeds were recovered from manure heated at 50 degrees C, and no viable seeds were recovered more than 2 days after dosing. Percent viability of seeds recovered from manure dried at 35 degrees C ranged from 0 to 22%. In both trials, percent viability of recovered seeds was lower compared with seeds that did not pass through animals. Sheep and mule deer can ingest, transport, and disseminate viable seeds of spotted knapweed in their feces.

Semiarid steppe communities in North America appear particularly vulnerable to persistent infestations by exotic, taprooted forbs, such as European spotted knapweed (Centaurea maculosa). We determined whether species differences in ecophysiological response to water availability could help link traits of Centaurea with invasibility of steppe communities. Plant-soil water relations and photosynthesis were measured under three water levels in a greenhouse and at two sites over two years in the field for Centaurea and dominant rangeland species of southwestern Montana: Pseudoregneria spicata, Pascopyron smithii, and Bromus inermis. Centaurea had greater and more seasonally persistent photosynthesis than the other species under field conditions but not in the greenhouse, where water availability was similar for the species. Centaurea had no greater water use efficiency, except under unusually dry conditions, but maintained greater water potentials despite greater transpiration than the grasses. Changes in soil water indicated uptake from deeper and wetter soils in Centaurea than in grasses. Greater photosynthesis in Centaurea compared with grasses may result from uptake of deeper soil water and corresponding drought avoidance. Interspecific differences in resource use may therefore contribute to the success of Centaurea, and Centaurea's ecological requirement for water matches an available resource niche in the communities we examined.

Spotted knapweed (Centaurea maculosa Lam.) is an invasive plant that alters species composition and grazing value of rangelands in the northwestern United States. The spread of invasive plants may be reduced by using livestock as a biological control. We determined if mature ewes and their lambs (n=34ewe/lamb pairs) consume more spotted knapweed when ewes and/or lambs are conditioned to fresh-cut spotted knapweed. Ewe/lamb pairs were randomly assigned to one of four conditioning treatments: ewes and lambs not conditioned to spotted knapweed (N), conditioned ewes with non-conditioned lambs (E), non-conditioned ewes with conditioned lambs (L), or conditioned ewes and lambs (both—B). Then, ewes and lambs were observed together for 5 days (Trial 1); 11 days later, lambs were observed for 4 days without their mothers (Trial 2). During conditioning, intake by conditioned and non-conditioned ewes and lambs varied over time (as-fed basis, treatment by day interaction; ewes P=0.03; lambs P=0.05). Overall, non-conditioned lambs (N, E) consumed more than conditioned lambs (L, B; P=0.02). In Trial 1, N ewes consumed similar amounts of spotted knapweed and bromegrass (Bromus inermis Leyss.) as the E, L, and B ewes (P=0.67). E ewes spent more time eating spotted knapweed than L ewes (P=0.001), and E ewe/lamb pairs consumed more spotted knapweed than L ewe/lamb pairs (P=0.02). In Trial 2, N lambs consumed less spotted knapweed than E, L, and B lambs (P=0.06). L lambs consumed more than E lambs (P=0.007). Conditioning ewes, lambs, or ewes and lambs did not increase time spent eating spotted knapweed when both grazed together in a drylot, but conditioned lambs, without their mothers present, consumed more spotted knapweed 11 days later than non-conditioned lambs. Conditioning lambs only in a group setting with their peers may have the greatest potential to enhance consumption of spotted knapweed, because of social facilitation and the predilection for young animals to try novel feeds.

Beef cattle grazing semiarid foothill rangeland of the Northern Rockies during winter may be exposed to cold temperatures and high winds while grazing pastures with low nutritional value. Cattle can physiologically and behaviorally respond to the changing environment to lower their metabolic requirements and reduce the effects of cold exposure. Requirements of grazing cattle may be overpredicted with models developed in controlled settings that do not account for energy-conserving behaviors. We refined a simple thermal balance equation to model heat exchange of free-ranging cattle. We accounted for the complex interactions between animal behavior and the changing natural environment by applying the insulation characteristics of the cattle's tissue and coat to a simple geometric shape of an asymmetric ellipsoid at different orientations to the sun and wind. We compared the model predictions with heat production measured in 3 studies, and in all cases the model predictions were similar to those reported. Model simulations indicate behaviors, such as lying and orientation to the sun, mitigated the effects of extreme weather. For many combinations of winter weather variables, metabolic requirements increased only slightly due to cold exposure of mature beef cattle in a near-maintenance state. The results indicate that solar radiation contributes strongly to the thermal balance of a cow. Thus, previous models that do not account for the irradiative environment may overestimate metabolic requirements of cattle acclimated to grazing winter range.

Invasions by exotic forbs are changing large areas of North American grasslands, but their biogeochemical impacts are not well characterized. Additionally, although many invasive plants may alter biogeochemistry, an invasive species’ effects have rarely been evaluated across physically diverse sites. We sampled nine sites containing the perennial Eurasian forb Centaurea maculosa to determine if this invasive species alters soil C and N pools in native grasslands in Montana, USA. We sampled surface soil in adjacent microsites with C. maculosa and native grasses and analyzed soil C and N pools with slow to rapid turnover. None of the pools evaluated in the laboratory showed significant differences between C. maculosa and grass microsites when analyzed across all sites. Some differences were found at individual sites, but they were infrequent and inconsistent: Four sites had no differences, four had differences in one or two pools with intermediate (particulate organic matter C or N) or rapid turnover rates (potentially mineralizable N), and just one site had differences encompassing pools with rapid, intermediate, and slow (total C and N, silt-and-clay-associated N) turnover rates. Where they differed, pools were usually smaller under C. maculosa plants than under native grasses, but the opposite was found at one site. In situ N availability, estimated using ion exchange resins, was significantly lower under C. maculosa than under grasses at one of three sites sampled. Results indicate that C. maculosa may sometimes reduce soil C and N pools, including those related to N availability, but they argue against generalizing about the impacts of C. maculosa in grasslands.

Nitrogen is often a limiting resource on semi-arid grasslands. During the growing season, N is often only available during short-term pulses associated with wetting events. The Eurasian forb Centaurea maculosa Lam. has invaded millions of hectares of semi-arid grasslands in western North America. C. maculosa's success could be attributed to greater use of N-pulses, or more efficient use of N supplied in those pulses compared with native grasses. In a glasshouse, C. maculosa and two native grasses, the caespitose Pseudoroegneria spicata [Scribn. and Smith] A. Love and the rhizomatous Pascopyrum smithii [Rybd.] A. Love, were established in mixed- and monoculture combinations, and then conditioned to weekly N-pulses of 8, 24, or 72 h for 8 weeks. These pulse durations are typical on semi-arid grasslands. At the end of the 8 weeks, plants were exposed to 15N-labeled nitrate (15NO3−) for 8 h and harvested 16 h later to compare short-term root uptake of 15NO3−. C. maculosa did not have greater enrichment (atom % 15N), rate of 15N-uptake (μmol g−1 h−1), or 15N acquired (relative to 15N applied) than the grasses. C. maculosa's 15N-uptake per unit mass was relatively consistent across pulse durations, whereas 15N-uptake was lower at the longer pulse durations for the grasses. In general, C. maculosa acquired more of the applied 15N than P. spicata but less than P. smithii. 15N acquired was often influenced by the neighbour's identity. Regarding growth responses, C. maculosa produced more total biomass than the grasses, except for P. smithii plants growing with C. maculosa conditioned to 72 h pulses of N. Root mass ratios varied depending on the neighbor. Overall, C. maculosa used nitrogen less efficiently than the grasses. C. maculosa's success as an invasive species cannot be explained wholly by a greater response to N-pulses or more efficient use of N-pulses compared with native grasses with which it competes.

The Eurasian herb Centaurea maculosa Lam. has invaded millions of hectares of semi-arid grasslands in western North America. Its success may reflect that it may be more competitive than native species, it is not grazed by large herbivores, it was introduced without its native enemies, it may interfere with native species via allelopathy, or most likely some combination of these factors. Greater competitive ability could include greater use of limiting soil resources, such as water, or more efficient use of soil water, thereby inhibiting establishment, survival, and reproduction of native species. We measured water use and water-use efficiency of Centaurea and three native grasses, Pseudoroegneria spicata [Scribn. and Smith] A. Love, Pascopyrum smithii [Rybd.] A. Love, and Festuca idahoensis Elmer, in a glasshouse. Water-use efficiency was determined by the traditional measure of biomass produced per mass of water used, and by carbon-isotope discrimination (Δ). Centaurea did not use the most water, or use water more efficiently (based on biomass (g)/ water (kg) and carbon-isotope discrimination) than all three native grasses. We also determined carbon-isotope discrimination of Centaurea and dominant native grasses during the 1999 and 2000 growing seasons at three field sites. Centaurea rosettes had the lowest water-use efficiency (greatest carbon-isotope discrimination), followed by mature plants of Centaurea, and then native grasses. Water-use efficiency of mature Centaurea plants and native grasses was greater in late summer than early summer. Centaurea's success as an invasive species in North America cannot be attributed to greater use of soil water or greater water-use efficiency than native grasses.

Livestock may impact habitat quality for grasshoppers by reducing food availability and by altering microclimate and potential oviposition sites. A 5-year study was conducted to create consistent grazing impacts on replicated plots and measure their effects on plant cover, microclimate, and grasshopper abundance. Cattle were used to produce two levels of grazing intensity that were compared to ungrazed controls. Differences in plant cover were greatest immediately after grazing each summer, grasshopper microhabitats tending to be shadier, cooler, less windy, and more humid in the ungrazed plots. The grasshopper assemblage included five of the worst pest grasshopper species in North America: Ageneotettix deorum, Aulocara elliotti, Melanoplus sanguinipes, M. packardii, and Camnula pellucida. Most species had greater abundance on ungrazed pastures, particularly during the 4–6 weeks after grazing each year. However, A. elliotti was often more abundant in heavily grazed areas early in the year when early instars were present and in late summer when adults were predominant. There was no strong evidence that the effect of grazing on grasshopper abundance increased over the 5-year study. At this time, all changes in grasshopper numbers cannot be directly attributed to particular habitat characteristics that changed after grazing, but the results suggest that grazing management could be used to reduce pest grasshopper densities.

Centaurea maculosa Lam. (spotted knapweed), a Eurasian perennial forb, has invaded disturbed and undisturbed semiarid grasslands in the western United States. In the past, success in controlling C. maculosa and restoring invaded areas has been limited. Most research has addressed chemical aspects of invasive species interactions with soils, while potential impacts of altered soil physical properties on C. maculosa's success has not been studied. We hypothesized that the persistence of C. maculosa in semiarid rangelands might reflect an ability to alter site conditions. The objective of this study was to compare selected soil physical properties under C. maculosa-dominated and native perennial grass-dominated areas on semiarid grassland. We used six field sites in western Montana containing adjacent plots dominated by C. maculosa and by native perennial grasses. Soil physical properties including particle size fractions, bulk density, and hydraulic and thermal properties, as well as total organic carbon content, of near-surface soils were measured for each vegetation type. Soil physical properties seldom differed between C. maculosa- and native grass-dominated areas. When soil physical properties differed, the differences were inconsistent within and among sites. Presence of C. maculosa did not alter surface soil characteristics at our six sites, thus its persistence on these semi-arid grasslands cannot be explained by an ability to alter near-surface soil characteristics.

Grazers ingest seeds of invasive forbs and may contribute to their spread by depositing viable seeds in uninfested areas. Some mature seed pass through the gastrointestinal (GI) tract of ruminants, but grazers consume flowerheads of invasive species from anthesis to dehiscence. We collected seed from the Eurasian leafy spurge (Euphorbia esula L.) at 3 stages of maturity (soft dough, hard dough, mature). With seed collected from these different stages, our objectives were to determine effects of 1) rate of passage through the GI tract of sheep on leafy spurge seed recovery, germinability and viability, 2) residence time in sheep rumen on seed germinability and viability, and 3) acid pepsin digestion, simulating the lower GI tract, on seed germinability and viability after different residence times in the rumen. More seed from the later stages of maturity were recovered in the manure. The greatest number of seed recovered only represented 3.9% of the number of ingested seed. Few seeds were recovered after day 4. Soft dough seed in manure would not germinate and was not viable, whereas hard dough and mature seed collected from manure during the first 4 day were viable. Pepsin had a slight effect on the number of mature seed recovered, but eliminated viability of recovered seed. Viability of non-pepsin treated seed from the hard dough and mature stages declined with greater residence time in the rumen. Thus, managers should be aware that livestock ingesting hard dough as well as mature seed may be dispersing viable weed seed.

Large ungulates grazing native rangelands during winter must balance forage intake, a source of energy gain, with minimizing thermal stress, a source of energy loss. Another source of energy loss, energy expended, is related to time spent in different activities. Natural or man-made shelter may alter time spent in different activities. Our objectives were to determine if access to windbreaks altered diurnal activity patterns of beef cattle grazing a windy, foothill range site during winter, and if diurnal activity patterns could be related to weather. We observed diurnal activity patterns of cattle with and with out access to windbreaks (windbreak, nonwindbreak) for two winters on an exposed pasture in southwest Montana. Actual use of windbreaks was only recorded in Winter 2. Windbreak cattle did not use the windbreak until day 16; subsequently, time spent behind windbreaks ranged from 0 to 30%. Activity patterns of windbreak and nonwindbreak cattle differed in subtle ways, indicating they used similar behaviors to minimize energy expended and to maximize energy gain. Time spent grazing was inconsistent between the two winter trials, possibly reflecting large differences in body condition when they entered each winter. For individual groups, time spent grazing (Winter 1, 33–96%; Winter 2, 18–94%) and standing (Winter 1, 0–63%; Winter 2, 0–78%) varied widely on a day-to-day basis, reflecting either an immediate response to that day's weather, or possibly a compensatory response to the previous day’(s’) weather, especially following cold, windy days. Wind velocity had minimal effect on grazing time, presumably because high wind velocities were associated with relatively warm days, or the animals were in sufficient condition to tolerate high wind velocities. Instead of minimizing energy expended by lying down during extreme cold, cattle spent more time standing, which maximizes heat gain from solar radiation. During winter, cattle behavior is a tradeoff between maximizing energy gain (thermal and food) and minimizing energy loss (thermal and metabolic). Key words: Activity, behavior, cattle, shelter, thermal, weather