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.
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.
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