Search

Intake of animals grazing grass pasture is in part influenced by canopy density. Our objective was to determine the vertical distribution of dry matter and neutral detergent fiber (NDF) within temperate perennial grass swards. The study was conducted in 2004 and 2005 on a Piano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudolls). When leaf height of each grass reached 25 cm in spring, summer, and fall, canopy layers were harvested from 20 to 25, 15 to 20, and 10 to 15 cm. Differences in canopy density were usually not significant when precipitation was below normal. With abundant spring precipitation, quackgrass [Elymus repens (L.) Gould] had greater upper canopy density (1.9 mg dry matter [DM] [cm.sup.-3]) than any of the other grasses studied. Grasses typically grazed at shorter heights such as bluegrass (Poa pratensis L.) and perennial ryegrass (Lofium perenne L.) had greater density in the lower canopy layer (1.0-1.3 g DM [kg.sup.-1]). While soft-leaf tall fescue (Festuca arundinacea Schreb.), reed canarygrass (Phalaris arundinacea L.), and meadow fescue (Festuca pratensis Hurls.) had lower density in the upper canopy than timothy (Phleum pratense L.) and quackgrass in the spring, the reverse was true in the summer. Herbage NDF of grasses generally increased from the upper to lower canopy layer (mean difference of 50 g [kg.sup.-1]); perennial ryegrass and meadow fescue often had the lowest NDF throughout the canopy (range of 392452 and 418-469 g [kg.sup.-1], respectively). Pasture intake may benefit from a diverse species composition because animals can graze a mixture having optimum density and NDF throughout the canopy.

Effects of sucrose (Suc) concentration on fermentation kinetics and products were evaluated using 3 concentrations of Suc, with 1 concentration of isolated NDF from Bermudagrass fermented together in batch culture in vitro with rumen inoculum. Fixed amounts of medium and inoculum were the protein sources, so protein:Suc decreased with increasing Suc. Kinetics were calculated from gas production over 48 h in a randomized complete block design (n = 28), and product yield was evaluated with sampling every 4 h for 24 h in a split-split plot in time design (n = 84). Fermentation vial was the experimental unit. Increasing Suc increased the lag time of rapidly (P < 0.01) and slowly fermented (P < 0.01) fractions and tended to decrease the rate of gas production from the rapid fraction (P = 0.07). Gas production from the slow fraction decreased linearly with increasing Suc (P = 0.02), suggesting a decrease in NDF fermentation. Sucrose was the predominant substrate at [less than or equal to] 8 h of fermentation. Maxima for microbial CP (MCP) production were detected at [less than or equal to] 8 h of fermentation. At detected MCP maxima, MCP production increased linearly (P = 0.02) and total organic acids (sum of lactate, acetate, propionate, and butyrate; mmol) tended to increase linearly (P = 0.07) with increasing Suc. Maximum lactate production at 0 and 4 h increased (P = 0.01), and yield of lactate from Suc tended to increase, linearly (P = 0.09) with increasing Suc. At detected MCP maxima, yield of C in products (total organic acids, MCP, C[O.sub.2], C[H.sub.4], glycogen) from utilized Suc C declined linearly for total products (P = 0.01) and organic acids (P = 0.01) and tended to decline for MCP (P = 0.12) as Suc increased. This maybe a function of increased catabolic inefficiency of microbes with increasing Suc, as evidenced by increasing yields of lactate, or the use of C for products not measured. Product C yields were 1.28, 0.98, and 0.81 from lowest to greatest Suc inclusion, respectively. Values >1 indicate incorporation of C from the medium, likely from AA and peptides. The results support the premises that direct effects of Suc concentration and perhaps protein:Suc alter yields of fermentation products. That substrate concentration altered fermentation products and kinetics, possibly due to interactions with the run conditions, advises the clear definition of substrates and fermentation conditions to determine how the results integrate into our knowledge of ruminant nutrition. Key words: cattle, fermentation kinetics, fermentation product, nonfiber carbohydrate, rumen fermentation, sucrose

Studies assessing the impact of climate change have focused on plant production, but forage nutritive value, especially of legumes, has often been overlooked. The objective of this study was to determine the effect of increasing temperature and atmospheric C[O.sub.2] concentration on chemical composition and digestibility of rhizoma peanut (RP, Arachis glabrata Benth.) leaf and stem. In vitro digestible organic matter (IVDOM), neutral and acid detergent fiber (NDF and ADF), and lignin concentrations were determined for plants grown in all combinations of two C[O.sub.2] (360 and 700 µmol [mol.sup.-1]) and four temperature environments (baseline, or ambient temperature in the greenhouse, B; B + 1.5; B + 3.0; and B + 4.5°C). Forage was sampled every 6 to 8 wk during two growing seasons. Neither increasing C[O.sub.2] nor temperature affected leaf IVDOM, but stem IVDOM declined from 562 (B) to 552 g [kg.sup.-1] (B + 4.5) with increasing temperature in Year 1 and from 577 to 511 g [kg.sup.-1] in Year 2. Stem NDF increased with increasing temperature from 556 to 561 g [kg.sup.-1] in Year 1 and from 519 to 526 g [kg.sup.-1] in Year 2. Stem ADF (412 to 418 g [kg.sup.-1]) and lignin (80 to 93 g [kg.sup.-1]) increased linearly as temperature increased in 1 of 2 yr. Lignin as a proportion of NDF or ADF (lignin/NDF or lignin/ADF) accounted for a large proportion of the variation in stem IVDOM. The RP nutritive value decreases with increasing air temperature, but it is relatively unaffected by atmospheric C[O.sub.2] concentrations in the range studied., INCREASING ATMOSPHERIC C[O.sub.2] to near a doubling of current concentrations and an associated increase in temperature are among changes predicted to occur in the global environment as consequence of the [...]

Nonfiber carbohydrates (NFC) encompass a compositionally and nutritionally diverse group exclusive of those carbohydrates found in NDF. Their content in feeds has often been described as a single value estimated by difference as 100% of dry matter minus the percentages of CP, NDF (adjusted for CP in NDF), ether extract, and ash. A calculated value was used because of difficulties with assays for individual NFC, but it does not differentiate among nutritionally distinct NFC. Errors in NFC estimation can arise from not accounting for CP in NDF and when multipliers other than 6.25 are appropriate to estimate CP. Analyses that begin to distinguish among NFC are those for starch, soluble fiber (non-NDF, nonstarch polysaccharides), and low molecular weight carbohydrates (mono-and oligosaccharides). Many starch analyses quantify [alpha]-glucans through specific hydrolysis of [alpha]-(1 [right arrow] 4) and [alpha]-(1 [right arrow] 6) linkages in the glucan, and measurement of released glucose. Incomplete gelatinization and hydrolysis will lead to underestimation of starch content. Starch values are inflated by enzyme preparations that hydrolyze carbohydrates other than [alpha]-glucan, measurement of all released monosaccharides without specificity for glucose, and failure to exclude free glucose present in the unhydrolyzed sample. Soluble fiber analyses err in a fashion similar to NFC if estimation of CP requires multipliers other than 6.25, or if contaminants such as CP and starch have not been properly accounted. Depolymerization and incomplete precipitation can also decrease soluble fiber estimates. The low molecular weight carbohydrates have been defined as carbohydrates soluble in 78 to 80% ethanol, which separates them from polysaccharides. They can be measured in extracts using broad-spectrum colorimetric assays (phenol-sulfuric acid assay or reducing sugar analysis of acid hydrolyzed samples) or chromatographic methods. Limitations of the colorimetric assays include lack of differentiation among mono- and oligosaccharides and differences in efficacy of measuring total carbohydrate. More sensitive and precise chromatographic methods require expensive equipment and specialized expertise. Current methods for NFC can separate nutritionally relevant fractions, but questions remain as to which fractions merit analysis and what analyses to use. These issues must be resolved in order to soundly evaluate and explore the roles of carbohydrates in diets. Key Words: Analytical Methods, Carbohydrates, Fiber, Starch, Sugars

Eight dual-flow continuous-culture fermenters were used to evaluate the effect of neutral detergent-soluble carbohydrates (NDSC) on fermentation by ruminal microorganisms. Citrus pulp and hominy feed were added to a basal diet as sources of NDSC, with citrus pulp providing neutral detergent-soluble fiber (NDSF) in the form of pectic substances and with hominy feed in the form of starch. The basal diet contained 26.7% corn silage, 6.0% alfalfa hay and 3.8% cottonseed hulls on a DM basis. The dried citrus pulp diet contained on a DM basis 17.2% CP, 34.7% NDF, 33.7% NDSC, and 14.4% NDSF, whereas the hominy feed diet contained 17.9% CP, 33.2% NDF, 35.9% NDSC, and 8.8% NDSF. Organic matter, DM, and NDF and ADF digestion were not affected by source of carbohydrate. Ammonia N concentration was greater (P Key Words: Citrus, Fermentation, Hominy, Nitrogen, Pulps, Rumen