To identify and quantify the influence of sward structure on the intake of grazing animals requires an understanding of sward-animal interactions at the bite level. We tested the hypothesis that bite dimensions on vertically heterogeneous swards are determined by structural characteristics of the top leaf stratum, independent of those of a bottom layer of pseudostem or stem. Dallisgrass (Paspalum dilalatum Poir.) microswards were constructed by hand in a factorial combination of two lamina lengths (5 and 8 em) and two sward heights (8 and 16 em). Tillers consisted of a top segment of lamina and a bottom one of pseudostem (Exp. l) or stem (Exp. 2) of length equal to the difference between sward height and lamina length. Treatments were replicated over three steers (Bos taurus) of 750 kg avg. body weight. Bite area and depth increased with sward height in swards with pseudostem but were not affected by lamina length. Pseudostems were not a barrier to defoliation and did not affect bite dimensions. Steers restricted grazing of tillers with stem to the upper lamina horizon. Bite depth was limited by stems only when lamina length was less than half of sward height. Bite area was reduced by the presence of stems because tillers bent at ligule height, restricting the animals to gather fewer tillers in each bite than when tillers bent at the base. Bite weight was reduced severely in swards with stem, relative to those with pseudostem. Results confirmed the importance of stem horizons and their relative positions in the sward as determinants of bite weight. P ROGRESS IN UNDERSTANDING the sward structural determinants of instantaneous (dry matter) OM intake rate (IIR) by grazing animals requires better knowledge of sward-animal interactions at the individual bite level. Within a limited range of sward conditions, grazing animals can adjust for sward-induced reductions in bite OM weight by increasing biting rate and/or daily grazing time (Chacon and Stobbs, 1976;Hodgson, 1985;Penning et al., 1991). Beyond these E.R: Flort:s, Universidad Nacional Agraria,

Whether foraging on pastures or rangelands, herbivores encounter plant species that differ in their concentrations of nutrients. They also all contain various secondary compounds that at too high doses can be toxic, but at the appropriate dose many of these toxins may have medicinal benefits. The quantity of forage an animal consumes depends on the other forages it selects because nutrients and toxins interact. Food intake also depends on an individual's morphology and physiology, and marked variation is common, even among closely related animals, in needs for nutrients and abilities to cope with toxins. Thus, individuals can better meet their needs when offered a variety of foods that differ in nutrients and toxins than when constrained to a single food. Nonetheless, we have focused on a few species, often grown in monoculture, and we have reduced concentrations of secondary compounds with little appreciation for their roles in protecting plants against herbivores, pathogens, and competitors. In nature, where diversity of plants is the rule and not the exception, eating a variety of foods is how animals cope with, and may benefit from, secondary compounds. The potential benefits of creating mixtures of plant species whose nutrient and secondary compound profiles complement one another are obvious, though much remains to be learned about how to reconstruct agro‐ecosystems with plants that complement and enhance one another structurally, functionally, and biochemically.

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North American birdsfoot trefoil (BFT, Lotus corniculatus L.) cultivars such as Norcen produce forage with low condensed tannin (CT) concentrations that may be insufficient for optimal livestock performance. Our objective was to identify European‐ and Mediterranean‐derived cultivars with higher CT concentrations that would be suitable for production in the colder continental United States. One alfalfa (Medicago sativa L.) and 14 BFT cultivars were established during 2005 in MI, UT, WI, and WV and harvested under a two‐ or three‐cut management to determine herbage chemical composition in 2006 and dry matter yield (DMY) in 2006 and 2007. During 2006, variances in crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were mainly influenced by location‐harvest environments, while CT was influenced by both cultivar and environment. Earlier‐maturing cultivars such as Bokor, AU Dewey, Rodeo, and Grasslands Goldie produced herbage with relatively high CT concentrations, but not undesirably low CP or high NDF, ADF, and ADL concentrations compared with Norcen BFT or alfalfa. By the second full production year in 2007, total DMY in UT exceeded WI by twofold and MI by ninefold, and total DMY of the moderate CT‐containing cultivar Lotar surpassed most other cultivars, suggesting it may be well suited for forage production in the United States. Yields of alfalfa in all environments exceeded BFT by about 1.5‐fold. Additional studies are needed to identify optimal CT concentrations in BFT for ruminants and to improve the compositional uniformity and yield of harvested BFT in various environments.

Consumer liking, proximate composition, pH, Warner-Bratzler shear force, fatty acid composition, and volatile compounds were determined from the LM (longissimus thoracis) of cattle ( = 6 per diet) finished on conventional feedlot (USUGrain), legume, and grass forage diets. Forage diets included a condensed tannin-containing perennial legume, birdsfoot trefoil (; USUBFT), and a grass, meadow brome ( Rehmann; USUGrass). Moreover, representative retail forage (USDA Certified Organic Grass-fed [OrgGrass]) and conventional beef (USDA Choice, Grain-fed; ChGrain) were investigated ( = 6 per retail type). The ChGrain had the greatest ( < 0.05) intramuscular fat (IMF) percentage followed by USUGrain, the IMF percentage of which was greater ( < 0.05) than that of USUGrass and OrgGrass. The IMF content of USUBFT was similar ( > 0.05) to that of both USUGrain and USUGrass. Both grain-finished beef treatments were rated greater ( < 0.05) for flavor, tenderness, fattiness, juiciness, and overall liking compared with USUGrass and OrgGrass. Consumer liking of USUBFT beef tenderness, fattiness, and overall liking were comparable ( > 0.05) with that of USUGrain and ChGrain. Flavor liking was rated greatest ( < 0.05) for USUGrain and ChGrain, and that of USUBFT was intermediate ( > 0.05) to those of ChGrain, USUGrass, and OrgGrass. Cumulative SFA and MUFA concentrations were greatest ( < 0.05) in ChGrain and USUGrain, whereas USUGrass and OrgGrass had lower ( < 0.05) concentrations. Concentrations of cumulative SFA and MUFA in USUBFT were intermediate and similar ( > 0.05) to those of USUGrain and USUGrass. Each forage-finished beef treatment, USUGrass, OrgGrass, and USUBFT, had lower ( < 0.001) ratios of -6:-3 fatty acids. Hexanal was the most numerically abundant volatile compound. The concentration of hexanal increased with increasing concentrations of total PUFA. Among all the lipid degradation products (aldehydes, alcohols, furans, carboxylic acids, and ketones) measured in this study, there was an overall trend toward greater quantities in grain-finished products, lower quantities in USUGrass and OrgGrass, and intermediate quantities in USUBFT. This trend was in agreement with IMF content, fatty acid concentrations, and sensory attributes. These results suggest an opportunity for a birdsfoot trefoil finishing program, which results in beef comparable in sensory quality with grain-finished beef but with reduced -6 and SFA, similar to grass-finished beef.

Herbage soluble carbohydrate (SC) levels vary diurnally and livestock intake can be higher for herbage harvested or allocated to animals in the evening than in the morning. Few assessments of SC and digestibility patterns have been made during sward depletion in rotationally stocked orchardgrass (Dactylis glomerata L.). We tested the hypothesis that simulated evening daily pasture allocation increases 24-h mean herbage SC and digestibility levels relative to morning allocation. Total nonstructural carbohydrate (TNC) and in vitro true dry matter digestibility (IVTDMD) levels were compared during 24-h clipping sequences initiated at 1900 h (PM) and 0700 h (AM). Sward height was progressively reduced from 40 to 8 cm at 6-h intervals in October, June, and August. Successively lower horizons from defoliation sequences and also from control areas that were not under progressive defoliation were analyzed. Digestibility and TNC levels varied diurnally and seasonally, and were often higher for PM sequences, but differences among 24-h means were small. Daily mean TNC levels for defoliation sequences initiated in PM and AM were 138 vs. 132, 93 vs. 88, and 72 vs. 60 g kg' in October, June, and August, respectively. In all periods, digestibility decreased from approximately 920 to 800 to 890 g kg' during sward depletion and displayed similar patterns between defoliation sequences. Patterns of TNC and digestibility during sward depletion may not be represented by those in intact swards, and PM allocation of daily herbage may not increase 24-h mean dietary TNC density relative to AM allocation. Daily quantities of ingested TNC could be higher for PM herbage allocation if livestock consume proportionately more herbage in the PM than we simulated. M ANAGEMENT OF GRAZING SYSTEMS for high animal performance includes facilitation of high intakes of pasture dry matter (DM) by livestock. Constraints to grazing animal performance include sward structural and herbage compositional factors that determine rates and concentrations of dietary energy intake (Orr et al., 1997;Vazquez and Smith, 2000;Barrett et al., 2001). Herbage SC and digestibility concentrations, two indices of dietary energy density, usually vary diurnally according to daily patterns of photosynthesis, respiration, and translocation of SC. In temperate climates, herbage SC concentrations are generally highest in evening and low-

Th e high cost of transportation fuels and the environmental risks associated with acquiring and using nonrenewable energy sources have created a demand for developing renewable bioenergy crops. Switchgrass (Panicum virgatum L.), a warm-season perennial grass, is a promising feedstock due to its high biomass production under a wide range of growing conditions and its satisfactory forage quality and chemical composition. West Virginia contains vast expanses of reclaimed surface mine lands that could be used to produce switchgrass as a bioenergy feedstock. Th is study determined dry matter yields of three switchgrass varieties (Cave-In-Rock, Shawnee, and Carthage) during the second to fourth years of production. Two research sites were established on reclaimed surface mines in southern West Virginia: Hobet and Hampshire. Th e Hobet site was prepared using crushed, unweathered sandstone as the soil material, and yields were signifi cantly lower at 803 kg ha −1 averaged across varieties and years than annual yields at Hampshire. Th e highest yield at Hobet, with Shawnee in the third year, was 1964 kg ha −1 . Th e Hamphire site, which was reclaimed in the late 1990s using topsoil and treated municipal sludge, averaged 5760 kg ha −1 of switchgrass across varieties and years. Th e highest yield, obtained with Cavein-Rock during the third year, was 9222 kg ha −1 . Switchgrass yields on agricultural lands in this region averaged 12,000 kg ha −1 . Although average switchgrass yields at Hampshire were about 50% lower than agricultural lands, they were greater than a target yield of 5000 kg ha −1 , a threshold for economically feasible production. Yields during the fourth year from a two-harvest per year system were not signifi cantly diff erent from a single, end-of-year harvest at both sites. Reclaimed lands show promise for growing bioenergy crops such as switchgrass on areas where topsoil materials are replaced and amended like that at the Hampshire site.

Herbage nonstructural carbohydrates (NC) contribute to livestock performance and silage fermentation. Knowledge of the distribution patterns of NC and other nutritional constituents in orchardgrass (Dactylis glomerata L.) swards could support harvest management decisions. Our objective was to determine diurnal and vertical patterns of total NC (TNC), crude protein (CP), and neutral detergent fiber (NDF) concentrations, and in vitro true dry matter digestibility (IVTDMD) and NDF digestibility (NDFD) in orchardgrass swards in October, June, and August. Herbage was sampled at 6-h intervals between 0100 and 1900 h from horizons positioned 40 to 27, 27 to 18, 18 to 12, and 12 to 8 cm above soil surface. Herbage composition varied among horizons in all months, and diurnally only in June and August. In June and August, only TNC with maxima of 109 to 123 g kg 21 at 1900 h exhibited consistent diurnal patterns. Swards harvested to residual heights of 18, 12, or 8 cm exhibited little spatial variation in TNC during June and August, but CP, NDF, and IVTDMD varied with harvest depth on all dates. As swards were harvested to successively greater depths, TNC increased in October, but not in June and August. In contrast, CP and IVTDMD decreased, and NDF increased, for harvests to successively greater depths in all months. For harvests in June and August, manipulation of depth would capture more variation in CP, NDF, and IVTDMD, but manipulation of time of day of harvest would capture more variation in TNC to meet animal performance and silage fermentation requirements.