In Vitro Dry Matter Disappearance Research Articles

In vitro dry matter disappearance using roe deer inocula from summer and winter

In vitro dry matter disappearance (IVDMD) of 12 forages were determined using ruminai inocula from 10 European roe deer (Capreolus capreolus L.) collected in summer and winter. There was significant difference in the ability of winter and summer inocula to digest winter and summer forages respectively. Each of the 6 summer forages had a significantly higher IVDMD in ruminal inocula of animals collected in summer versus winter. However, no significant difference in IVDMD of winter versus summer inocula was observed for each of the 6 winter forages. These results suggest adaption, although limited, by ruminal microorganisms in roe deer to winter forages or a potential problem in standard in vitro laboratory procedures when using animals on a high-fiber diet as inocula donors.

Dry Matter Concentration as an Index of in Vitro Dry Matter Disappearance in Bermudagrass

Simple and cost‐effective procedures for predicting forage quality are needed. The objective of this study was to determine if dry matter concentration (DMC) could be used as an index of in vitro dry matter disappearance (IVDMD)in bermudagrass (Cynodon spp.). Data were from two bermudagrass trials at Tifton, GA. The 1983 and 1985 trials contained 32 and 28 entries replicated five times. Plots were harvested four times a year for 3 yr, except in 1987 when only three harvests were taken. A negative correlation was observed between DMC and IVDMD. Coefficients of determination (r2) from the regression of entry mean IVDMD on DMC from individual harvests ranged from 0.01 to 0.82. Entry DMC means averaged across harvests within years provided consistent index of IVDMD(r2 = 0.20, 0.65, 0.49, 0.57, 0.60, and 0.59). Regression coefficients differed among groups of bermudagrass entries having different genetic backgrounds. When screening bermudagrass entries for forage IVDMD, ≈50% of the entries could be eliminated based on forage DMC if the entries are replicated over space and time.

Yield and Quality of Silage Corn as Altered by Johnsongrass Infestation

AbstractDairy and beef producers in the southern piedmont region of the USA with limited land often grow corn (Zea mays L.), after corn, for silage even though stands gradually become infested with johnsongrass [Sorghum halepense (L.) Per.]. The objective of this study was to quantify the influence of johnsongrass infestation on the yield and quality of corn grown for silage. Seven field trials were conducted over a 6‐yr period in the piedmont region of North Carolina on clayey, kaolinitic, thermic, Typic Hapludult soils. Corn was planted each year into johnsongrass‐infested sites. Herbicides were used to produce johnsongrass‐free plots and plots where johnsongrass was the only weed present. Additionally, to assess the influence of johnsongrass infestation level on the subsequent silage quality, physical mixtures of corn and johnsongrass forage were made which represented an infestation range from 0 to 100% by weight. In five of seven trials, corn forage yield was significantly increased with johnsongrass control. Where johnsongrass was not controlled, corn plant population was reduced by 13% and silage quality, estimated by in vitro dry matter disappearance (IVDMD), was reduced by 8 to 21%. Silage IVDMD decreased linearly 2.37 g kg−1 (r2 = 0.95, P < 0.001) for each percentage unit increase in johnsongrass infestation by weight.

Hemicellulosic cell wall carbohydrate monomer composition in Panicum amarum, P. amarulum and P virgatum accessions

AbstractThree taxa in the Virgata group of Panicum, ie Panicum amarum (Elliot) var amaruns (Hitch and Chase) P. G. Palmer, and P virgatum L, show potential as a ruminant feed. Accessions analyzing high and low in‐vitro dry matter disappearance (IVDMD) were selected from three morphological categories of short (grazing types), intermediate, and tall (hay types) from among these taxa. Significant structural carbohydrate variation existed among accessions and within plant and morphological categories. Significant differences in hemicellulosic monomer concentrations were also found for maturity stages and accessions differing in IVDMD. Total hydrolyzed hemicellulosic pentoses(arabinose+xylose) of plant parts were negatively correlated (r = –0.77, P ≤ 0.01) with IVDMD in contrast to hemicellulosic hexoses (galactose + glucose) which were positively related (r = 0.40, P ≤ 0.01). Similar significant (P ≤ 0.001) correlations for whole plant samples were r = –0.86 and 0.39, respectively. Of the hemicellulosic monomers, xylose and glucose accounted for most variation in IVDMD. The hydrolyzed hemicellulosic pentose fraction or a ratio between the xylose and glucose composition were indicators of IVDMD and would be useful in the selection of germplasm to develop improved Panicum ecotypes.

Effects of chemical treatments of cereal grains on in vitro dry matter disappearance and steer feedlot performance

In four in vitro trials, the effectiveness of different chemical treatments in protecting cereal grains from ruminal degradation was studied. Corn, wheat and oats were treated by mixing with either 0, 0.5, 1 or 1.5% (w/w) formaldehyde, formaldehyde plus propionic acid, propionaldehyde, propionaldehyde plus propionic acid or propionic acid. The combinations of aldehydes plus propionic acid were in a 3:1 ratio. Corn, wheat and oats were also treated with 0, 2.5 or 3% propionaldehyde or combinations of propionaldehyde and sodium or ammonium hydroxide. Formaldehyde, either alone or in combination with acid, consistently reduced in vitro dry matter disappearance (IVDMD) of cereal grains. Propionaldehyde alone or in combination with either acid or alkali was less effective than formaldehyde in restricting fermentation. Although formaldehyde treatment of cereal grains reduced dry matter disappearance in vitro, treatment of the corn included in concentrate diets fed to growing steers produced no difference in their performance.

Forage sorghum silage dry matter disappearance as influenced by plant part proportion

Forage sorghum ( Sorghum bicolor (L.) Moench) is widely grown for silage in the High Plains region of the U.S.A. The in vitro dry matter disappearance (IVDMD) dynamics of forage sorghum silage, as influenced by the proportion of ensiled plant parts, were examined. Five mid- to late-season forage hybrids were grown at Manhattan, Kansas, on a Smolan silty clay loam (fine, montmorillonitic, mesic Typic Agriustoll) in 1987. The hybrids were harvested at the hard dough stage of maturity. Grain yields ranged from 4.18 to 5.23 Mg ha −1, and silage yields from 13.72 to 16.45 Mg ha −1. At ensiling, five plants per hybrid were separated into grain, leaf, sheath and stalk parts, chopped, put into nylon bags and ensiled with their respective silages in pilot silos. The distribution of dry matter (g kg −1) among the plant parts was grain 282–413, leaf 208–229, sheath 107–170, stalk 195–401. The pH of each silage and plant part was determined at silo opening. The IVDMDs of plant parts were grain 769, leaf 577, sheath 527 and stalk 608 g kg −1, and ranged from 582 to 617 g kg −1 for silages. For each silage, each plant part was individually increased to unity, then the IVDMD dynamics were plotted. The silages were reconstituted and the IVDMD determined. These ranged from 633 to 677 g kg −1. Statistically, the reconstituted silage IVDMD is the sum of the plant part IVDMD values, but the actual silage IVDMD was not. Regression equations were generated to predict silage IVDMD based on the proportion of plant parts for each hybrid. Grain had the greatest and a positive effect on silage IVDMD dynamics, whereas the sheath component had a negative effect.

Cytology, Reproductive Behavior, and Forage Potential of Hexaploid Dallisgrass Biotypes

During the past 25 yr, several different dallisgrass (Paspalum dilatatum Poir.) biotypes have been discovered, but little is known regarding their cytology and reproductive behavior. This study was undertaken to determine the cytology, method of reproduction, and fertility of three biotypes and the forage yield and quality of two of them. Two biotypes, Torres and Uruguaiana, were introduced from southern Brazil and the third, Uruguayan, was collected in Uruguay. All three are hexaploids with 2n = 6x = 60. The Torres biotype was meiotically irregular, with a mean chromosome association of 58.74 univalents and 0.63 bivalents per cell. Two accessions of the Uruguaiana biotype were studied; they had a mean meiotic chromosome association of 9.62 univalents, 25.17 bivalents, and 0.01 quadrivalents. Eleven accessions of the Uruguayan biotype were studied; their mean chromosome associations were 1.26 univalents, 29.28 bivalents, and 0.04 quadrivalents. It was proposed that the lack of chromosome pairing in the Torres biotype is genetically controlled. The genomic formulas of the Uruguaiana and Uruguayan biotypes are proposed to be AABBC1C2 and AABBCC, respectively. An examination of megasporogenesis and embryo sac development revealed that all three biotypes reproduce by apomixis, with apospory followed by pseudogamy. One Uruguayan accession was a facultative apomict with a small degree of sexuality. The forage yield potential and forage quality were determined for the Torres and Uruguayan biotypes, as well as for common dallisgrass. Torres produced less forage than the other two. Common dallisgrass produced less forage than the mean of the Uruguayan accessions in most environments. In vitro dry matter disappearance (IVDMD) differences among accessions were relatively small. Common dallisgrass did not differ in IVDMD from any of the Uruguayan accessions.

Nitrogen Effects on Yield and Forage Quality of Perennial Ryegrass and Tall Fescue

AbstractNegative animal effects of tall fescue (Festuca arundinacea Schreb.) infected (EI) with the endophytic fungus Acremonium coenophialum Morgan‐Jones and Gams are reduced by substituting endophyte‐ free (EF) tall fescue or other forage species. A field experiment was conducted on Maury silt loam (fine, mixed, mesic, Typic Paleudults) soil from 1986 to 1988 to compare forage yields and quality of ‘Kenhy’‐EF, Kenhy‐EI, and ‘Johnstone’ tall fescue with ‘Ensilo’ (diploid) and ‘Reveille’ (tetraploid) perennial ryegrass (Lolium perenne L.) and ‘Bison’ ryegrass (Lolium intermediate). Each cultivar received 0, 75, or 150 kg ha−1 of N annually. At 150 kg ha−1 of N, Johnstone produced the highest 1987 to 1988 average dry matter (DM) yields of 6.7 Mg ha−1 compared with 5.7 Mg ha−1 for Kenhy‐EI. Tall fescue generally produced higher yields than ryegrass. Ground cover after 3 yr for Reveille of 72% did not differ from Kenhy‐EI (79%), but Ensilo (61%) and Bison (31%) were lower. Endophyte effects on yield and quality of Kenhy were seldom significant. Two‐year weighted average in vitro dry matter disappearance (IVDMD) values were 685, 663, 626, 628, and 641 g kg−1 for Reveille, Ensilo, Kenhy‐EF, Kenhy‐EI, and Johnstone, respectively. Increasing N levels increased N concentration of tall fescue but did not consistently affect that of ryegrass. These results indicate that some cultivars of ryegrass can persist at this location, but that summer productivity is well below that of tall fescue. However, some potential may exist for germplasm improvement of perennial ryegrass based on existing cultivars. Endophyte effects on yield and quality of Kenhy tall fescue under the conditions of this study were small.

Relationship of lignin and esterified phenolics to fermentation of smooth bromegrass fibre

The importance of concentration and composition of lignin and esterified phenolics in forage cell walls was investigated relative to limitation of fibre fermentation. Smooth bromegrass ( Bromus inermis Leyss.) leaf and stem tissues were analyzed for in vitro fermentability of detergent fibre fractions. The smooth bromegrass samples represented nine genotypes selected for high in vitro dry matter disappearance (IVDMD) and nine genotypes selected for low IVDMD. Lignin was an important predictor of fibre fermentation for stems but not for leaves. The relationships of stem neutral detergent fibre and hemicellulose, but not cellulose, fermentability to lignin concentration were different between the high and low IVDMD genotype groups. Nitrobenzene oxidation products were negatively correlated with leaf blade fibre fermentation. Stepwise multiple regression analysis, within IVDMD genotype groups, showed no relationship between fibre fermentation and lignin/phenolic measures for leaves, and primarily a lignin concentration effect in high IVDMD stems. Major differences exist in the importance of lignin concentration, lignin composition, and esterified phenolics concentrations to fibre fermentability of smooth bromegrass genotypes selected for divergent IVDMD.

Effects of grass species on grazing steers: I. Diet composition and ingestive mastication.

In traditional grazing trials, per animal and per hectare productivity are determined, but pasture and animal measurements are generally inadequate to address reasons for different treatment responses. This 2-yr study examined the diet and diet characteristics of steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.) pastures. A randomized complete block design was used with two agronomic replicates. In vitro DM disappearance (IVDMD) of masticates from tall fescue (TF), switchgrass (SG), and flaccidgrass (FG) generally were similar; all exceeded 70% (70.3 to 79.9%), except for bermudagrass (BG), which was lowest (63.5 to 65.0%). Sieving the masticate DM showed BG to contain the highest proportion (20 to 29%) of particles passing a .5-mm sieve and the lowest proportion (6 to 8%) of particles retained on a 2.8-mm sieve. This resulted in BG having the smallest mean (1.29 mm) and median (1.08 mm) particle sizes in yr 1 and a mean (1.10 mm) and median (.91 mm) particle size smaller than SG in yr 2. Except for BG, the IVDMD of the masticate DM was lowest for small particles. Canopies showed BG and SG to have the highest proportion of stem (47 and 52%, respectively); the BG canopy was composed of fractions that were consistently lowest in IVDMD. In general, BG offered the grazing animal a canopy inferior in IVDMD concentration and had canopy characteristics that limited the animals' selection of a diet with quality as high as that of TF, SG, or FG.

Degradability of phenolic acid‐hemicellulose esters: A model system

AbstractA synthetic model system containing p‐coumaric and ferulic acids esterified to hemicellulose was used to study polysaccharide degradability. Oatspelts xylan was fractionated into Alinear, Blinear and Branched fractions prior to synthetic esterification with phenolic acids at treatment concentrations of 0, 25, 50, 75 and 100 g phenolic acid per kg hemicellulose. Concentrations of phenolic acids esterified to the hemicellulose fractions were determined by alkaline hydrolysis. In‐vitro dry matter disappearance (IVDMD) and degradability of hemicellulose neutral sugars were measured after 48 h ruminal fermentations. Esterification efficiency of the phenolic acids to the hemicellulose fractions was low (0.3 to 13.9%) and greater for p‐coumaric than ferulic acid (4.7 vs 3.1%, respectively). Concentration of esterified phenolic acids was negatively correlated with IVDMD for the Alinear and Bbranched fractions. Ferulic acid appeared to be more inhibitory to IVDMD than p‐coumaric acid. Generally the degradability of the side chain sugars of the hemicellulose fractions was negatively correlated with esterified phenolic acid concentrations. Xylose degradation was only correlated with esterified ferulic acid level in the Alinear fraction. The in‐vitro ruminal fermentations resulted in the degradation of the majority of the phenolic acid esters. Analysis of the synthetic phenolic acid‐hemicellulose esters by 13C NMR and FTIR was unable to prove the presence of monomeric phenolic acid esters. The presence of phenolic acid polyesters was unlikely because of the solubility of the synthetic phenolic acid‐hemicellulose esters. The neutral sugar degradation data suggest that esterification of the phenolic acids was limited to sugars with primary hydroxyl groups. While this model system was useful for studying cell wall degradation, future studies must employ model systems in which the chemical constituents being tested accurately model those found in nature.

Modification of in-vitro digestibility and cell-wall composition of cocksfoot, ryegrass and timothy by imazethapyr

Recent studies have shown that the compound imazethapyr (5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid) possesses growth regulatory activity and can be used to enhance nutritive value of grasses. However, little is known about possible effects of this material on fibre composition or potential fibre utilisation by ruminants. The objective of this research was to examine imazethapyr-treated cocksfoot (Dactylis glomerata L), ryegrass (Lolium perenne L × L multiflorum Lam), and timothy (Phleum pratense L) for possible treatment-induced changes in in-vitro digestibility and in concentrations of selected fibre constituents. Replicated field plots treated with imazethapyr at 0 (control) or 100 g ai ha−1 during the vegetative (pre-elongation) stage of growth were harvested when controls were in the early stage of inflorescence emergence. Samples taken from treated plots 4 weeks post-treatment had higher in-vitro dry matter disappearance (IVDMD), lower neutral detergent fibre (NDF), lower acid detergent fibre (ADF), lower cellulose, lignin, and higher hemicellulose concentrations compared with controls. Imazethapyr treatment also reduced the concentration of p-coumaric acid in NDF, but had no effect on ferulic acid. The treatment effect on in-vitro NDF disappearance, however, was inconsistent among the grass species and was statistically non-significant (P = 0·10), implying that, under the conditions of this study, imazethapyr-related enhancements in IVDMD can be attributed primarily to a reduction in the amount of NDF and its associated constituents, as opposed to qualitative differences in NDF composition.

Hay Curing and Water Soaking: Effects on Composition and Digestion of Alfalfa Leaf and Stem Components

Progress toward improved hay harvesting technology is limited by a lack of information on the sources of yield and forage quality losses that occur during curing of alfaffa (Medicago sativa L.) hay, especially with exposure to rain. Two trials were conducted to determine the relative contributions of separate leaf and stem components to losses in yield and quality and to changes in dry matter and cell‐wall digestibility of alfalfa during hay curing and soaking with water. Concentrations of N, ash, in vitro dry matter disappearance (IVDMD)1 and neutral (NDF) and acid (ADF) detergent fibers were measured for leaf and stem components from alfalfa herbage just after harvest, and for field‐cured and water‐soaked hay. Leaf concentration averaged 386, 330 and 280 g kg‐1 in herbage, dry hay, and soaked hay, respectively. Neither hay treatment affected component N concentrations but whole‐shoot N concentration was reduced in both hays due to reduced leaf concentrations. Increased component fiber concentrations and reduced leaf concentration in soaked hay both contributed to large NDF and ADF increases on a whole‐shoot basis. The extent and rate of NDF disappearance were reduced in soaked hay compared with herbage. Leaf accounted for 78% or more of the respiration and shatter losses of DM, N, ash, and in vitro digestible dry matter (IVDDM) and 60% or more of the soaking losses of the same constituents. Onethird of the leaf N content was lost in soaked hay compared with 10% of the stem N content. Leaf and stem each lost 3% of their NDF content. Ash content losses during soaking exceeded 50% for leaf and 30% for stem. Because nearly all of the respiration and shatter losses, and most of the soaking losses, of chemical constituents came from the leaf component, reducing leaf loss offers the greatest opportunity for reducing alfalfa hay harvesting losses. Productive value of hay might be impacted more by severe wetting than constituent concentrations alone would indicate becaus extent and rate of fiber digestion are reduced.

Effects of grass species on grazing steers: II. Dry matter intake and digesta kinetics.

Animal responses to treatments in grazing experiments frequently remain unexplained because of inadequate pasture and(or) animal measurements. This 2-yr study examined DMI, gastrointestinal tract fill of undigested DM (FILL), rate of digesta passage (ROP), and digesta mean retention time (MRT) for steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.). A randomized complete block design was used with two agronomic replicates. Comparisons in June (yr 1) among continuously grazed switchgrass (SG), flaccidgrass (FG), and bermudagrass (BG) or in May (yr 2) among tall fescue (TF), SG, and FG showed similar digesta kinetics, but different DMI (kg.d-1.100 kg BW-1), among these forages within each sampling. In the June evaluation, the DMI of SG and FG were similar (means = 3.09), DMI of bermudagrass (BG) was lowest (2.23), and fecal DM output (FO) was similar among forages. In the May evaluation, DMI by steers grazing SG (3.90) was higher than that by steers grazing FG (2.97); DMI of tall fescue (TF) was intermediate (3.41) but similar to DMI of FG. Differences in DMI were due to differences in diet in vitro DM disappearance (IVDMD) rather than to differences in digesta kinetics. In July (yr 2), the MRT was highest for BG (84 h) and similar for SG and FG (57 h). Steers grazing different forages exhibited similar ROP and FILL, but FO (kg.d-1.100 kg BW-1) among steers varied (.37 for steers fed BG; .74 for steers fed SG and FG).(ABSTRACT TRUNCATED AT 250 WORDS)

Yield Components, Morphology, and Forage Quality of Multifoliolate Alfalfa Phenotypes

Forage quality of alfalfa (Medicago sativa L.) maybe improved by increasing the proportion of leaves to stems. Our objective was to examine the influence of the moltifoliolate leaf trait on morphology, yield components, and forage quality of alfalfa. Multifoliolate plants selected for production of five, seven, or nine leaflets per leaf were compared to trifoliolate plants selected for rapid (RSER) and slow (SSER)shoot elongation rate that also exhibited low and high leaf/stem ratios, respectively. Herbage from field‐grown plants was sampled twice in each of two years. Leaves of multifoliolate plants averaged. 4.4, 6.2, and 6.8 leaflets per leaf for phenotypes FIVE, SEVEN, and NINE, respectively. In 1987 multifoliolate plants produced fewer shoots per plant (x̄ = 26) but phenotypes FIVE and SEVEN consistently produced larger shoots (x̄ = 2.0 g shoot−1) than the RSER phenotype(x̄ = 59 shoots plant−1, 1.3 g shoot−1. Leaf/stem ratio was lowest for phenotype RSER (0.63), while leaf/stem ratio of SSER (1.27) equalled that of phenotypes SEVEN (1.20) NINE (1.30). In vitro dry matter disappearance (IVDMD) of herbage of multifoliolate phenotypes and SSER was greater(P < 0.10) than that of phenotype RSER in 1986, while in 1987 IVDMD of herbage of phenotypes NINE and SSER exceeded that of RSER. Herbage N concentrations of multifoliolate plants were not consistently greater than that of phenotype RSER, and were associated with lower leaf N concentrations in multifoliolate plants. The multifoliolate plants used in this study had high leaf/stem ratios, but this trait was not consistently associated with improved forage quality. Environment,along with other plant characters, also influenced IVDMD and N concentrations of herbage of these plants.

Degradation of Switchgrass Anatomical Tissue by Rumen Microorganisms

Factors that influence rumen microbial degradation of switchgrass (Panicum virgatum L.) tissues are not well understood. Our objective was to measure and compare the anatomical degradation of leaf blades, leaf sheaths, and stems by tureen microorganisms. Two field‐grown switchgrass cultivars were harvested when three‐fourths of the inflorescence had emerged. Three‐millimeter portions of blade, sheath, and stem tissue were incubated in buffered rumen fluid for 0, 24, and 48 h, then removed and processed for light microscopy. Tissue composition and microbial degradation within each morphological component were measured with a computer‐based optical image analyzer. No differences in degradation were apparent between cultivars. The largest portion (35.7%) of blade cross‐sectional area was occupied by the mesophyll. After 48 h of incubation in rumen fluid, 32% of this tissue was partially degraded and 68% completely degraded. In contrast, leaf sheath parenchyma tissue was more resistant to complete degradation than that of the blade. In the sheath, 17.2% of tissues in the cross‐sectional area were at least 80% intact after 48 h of incubation; only 4.3% of the cross‐sectional area of the blade was this resistant to degradation. These differences in degradation resulted in lower (101 g kg−1) in vitro dry matter disappearance (IVDMD) in the sheath compared with the blade. Tissues (cortex, xylem, and bundle sheath) in which at least 80% of their area was intact after 48 h of incubation occupied 25.8% of the stem's cross‐sectional area. It is these resistant tissues that appear to cause the stem to have the lowest IVDMD of the three major morphological components of switchgrass. A detailed understanding of differences in degradation of anatomical tissues will result in the development of more digestible cultivars and morefficient forage utilization by livestock.

Lignin Concentration and Composition of Divergent Smooth Bromegrass Genotypes

Esterified phenolics of noncore lignin and core lignin concentration and composition are correlated with forage digestibility. In this study, divergent smooth bromegrass (Bromus inermis Leyss.) genotypes selected for high or low in vitro dry matter disappearance (IVDMD) were evaluated for genotypic variation of lignin concentration and composition. Primary growth of nine genotypes from each IVDMD selection group was harvested during 2 yrs and separated in to leaf blade and stem plus sheath fractions. Detergent fiber components, core lignin concentration and composition, and esterifled noncore lignin content were determined. Differences were observed between the IVDMD genotype groups for neutral detergent fiber (NDF), hemicellulose and cellulose concentration in leaf blade tissue, and NDF and hemicellulose concentration of stems. Core lignin concentration was greater in stem of the low IVDMD group but not leaves. Yield of core lignin products was greater for the low IVDMD group leaf blades but not stem plus sheath tissue. Genotypic variation existed between and/or within IVDMD genotype groups for molar proportions of vanillin, syringaldehyde, p‐coumaric acid, and ferulic acid from core lignin nitrobenzene oxidation products. Esterified ferulic acid concentration of noncore lignin was consistently greater in the high IVDMD group, but esterified p‐coumaric acid was only greater in stem tissue of the low IVDMD group. Differences observed between the IVDMD groups were generally consistent with previous reports of correlations between lignin fractions and IVDMD. Differential phenotypic correlation coefficients between lignin concentration and composition for the high and low IVDMD groups suggested some value to attempting divergent, independent selection for lignin concentration and composition. Resultant genetic materials would be valuable tools for addressing mechanistic questions about the role of specific lignin fractions as inhibitors of fiber fermentability.

MANIPULATING SEASONAL GROWTH DISTRIBUTION AND NUTRITIVE QUALITY OF TIMOTHY AND ORCHARDGRASS USING THE GROWTH REGULATOR IMAZETHAPYR

Other than timely defoliation, management options for cool-season grass forages are limited. The growth regulator, imazethapyr (5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid), was evaluated as an agent for modifying seasonal production and nutritive quality of timothy (Phleum pratense L.) and orchardgrass (Dactylis glomerata L.). In 1986, 1987, and 1988 field plots of Toro timothy and Pennlate orchardgrass were treated with imazethapyr (IM) at rates of 50 and 100 g a.i. ha−1, respectively. Three cutting treatments were imposed, involving a progressive delay of first harvest based on the growth stage of the controls. The 0 Delay, Delay 1, and Delay 2 harvests were made when controls were at early head, anthesis (13-d delay), and post-anthesis (26-d delay), respectively. At 0 Delay, imazethapyr treatment increased timothy in vitro dry matter disappearance (IVDMD) by as much as 80 g kg−1, crude protein (CP) by 27 g kg−1, and reduced neutral detergent fiber (NDF) by as much as 150 g kg−1 (3-yr average). Corresponding changes for orchard-grass were 50, 23, and 100 g kg−1, for IVDMD and CP augmentation and NDF reduction, respectively. Nutritive quality of treated Delay 1 forage was similar to that of 0 Delay controls, while that of Delay 2 forage declined substantially. Although first harvest yield was reduced approximately 50% by imazethapyr treatment, second harvests showed a treatment-related yield enhancement, resulting in similar seasonal production for both treated and control forage. Imazethapyr has potential as a management tool to defer timothy and orchardgrass hay harvest for up to 2 wk without incurring significant losses in yield or quality.Key words: Dactylis glomerata, Phleum pratense, forage production, forage quality, growth regultors

Composition and Yields of Alfalfa Fresh Forage, Field Cured Hay, and Pressed Forage

AbstractA mechanical dewatering process was developed to avoid losses in yield and quality incurred during field hay curing. A 4‐yr field study was conducted to gain information on factors affecting hay curing losses and to compare hay to mechanically dewatered alfalfa (Medicago sativa L.). Ten harvest regimes were imposed on alfalfa monocultures to provide a wide range of fresh forage compositions and of hay curing conditions. Over the 4 yr, hay averaged 31.0 g kg−1 of N, 3.3 g kg−1 less than herbage, but 3.7 g kg−1 higher than pressed forage. Hay in vitro dry matter disappearance (IVDMD) was 596 g kg−1, 10% less than herbage, but similar to pressed forage at 589 g kg−1. Pressed forage was highest in neutral detergent fiber (NDF) at 559 g kg−1 while fresh forage had 422 g kg−1 and hay had 518 g kg−1. The best single predictors of hay concentrations of N, NDF, and IVDMD were fresh forage concentrations of the same constituents. Other significant variables for prediction of hay composition included dry matter loss (DML) during hay curing, rain amount, and hay curing time. Since hay curing and pressing both affected NDF concentration more than IVDMD, preservation system effects on intake potential could be even greater than effects on digestibility. The finding that fresh forage quality is the primary determinant of alfalfa hay quality indicates that close attention to quality at the time of cutting should more consistently produce hay of the desired quality than would delaying harvest in an attempt to avoid rain. The pressed forage and the protein concentrate together produce yields similar to or greater than those of hay and reduce N losses by nearly one‐half.

Forage quality of five cool-season grasses. II. Species effects

A 2-year field experiment was conducted on established stands of smooth bromegrass ( Bromus inermis Leyss.), orchardgrass ( Dactylis glomerata L.), timothy ( Phleum pratense L.), tall fescue ( Festuca arundinacea Schreb.) and reed canarygrass ( Phalaris arundinacea L.) to evaluate maturity effects on quality. Herbage was sampled on seven dates during spring and early summer. Species did not differ in total N and all declined in N with shoot maturation. Timothy was highest in average in vitro dry matter disappearance (IVDMD) at 661 g kg −1 and orchardgrass was lowest at 615 g kg −1. Reed canarygrass and tall fescue declined more rapidly in IVDMD with maturation than timothy and smooth bromegrass. Orchardgrass had the highest average neutral detergent fiber (NDF) concentration at 624 g kg −1. Tall fescue had the lowest average NDF concentration, at 576 g kg −1, but reed canarygrass increased more rapidly in NDF with maturation than smooth bromegrass and timothy. Results of this experiment indicate that reed canarygrass and, to a certain extent, tall fescue changed more rapidly in IVDMD, NDF and acid detergent fibre (ADF) with maturation than the other species and thus would need to be utilized at an earlier stage of maturity to obtain forage of similar quality. Timothy and smooth bromegrass declined least rapidly in quality. Timothy had the highest average IVDMD, but tall fescue had a lower average NDF concentration indicating that species differences also exist in cell-wall digestibility.