Rate Of Fiber Digestion Research Articles

Effects of varying dietary ratios of corn silage to alfalfa silage on digestion of neutral detergent fiber in lactating dairy cows

An in vivo study was performed to test an in vitro procedure and model that predicts total-tract neutral detergent fiber (NDF) digestibility for lactating dairy cattle. Corn silage (CS) and alfalfa silage (AS) were used as forages for this study. These forages had similar NDF composition, but fiber in the CS contained less indigestible NDF compared with AS (35.5 and 47.8% of indigestible NDF, respectively). The in vitro method estimated rate of digestion of alfalfa potentially digestible NDF to be approximately 2 times faster than CS fiber (6.11 and 3.21%/h, respectively). Four diets were formulated containing different proportions of CS to AS: 100CS:0AS, 67CS:33AS, 33CS:67AS, and 0CS:100AS, as percentage of diet DM basis. The objective was to construct diets that contained approximately similar levels of NDF but with different pool sizes and rates of digestion of potentially digestible NDF. Diets were fed to 8 ruminally cannulated, multiparous, lactating dairy cows in a replicated 4×4 Latin square with 21-d periods. Total-tract fiber digestibility and fiber digestion kinetic parameters observed in vivo were compared with the values predicted by the in vitro assay and model. Total-tract NDF digestibility coefficients were similar (41.8 and 40.6% of total NDF) for the in vitro and in vivo methods, respectively. As the proportion of dietary alfalfa increased, the digestibility of NDF increased. The rate of digestion of potentially digestible NDF predicted from the in vitro assay was also similar to what was observed in vivo. Results suggest that the in vitro total-tract NDF digestibility model could be used to predict rate of fiber digestion and NDF digestibility for lactating dairy cattle.

Validation of an in vitro model for predicting rumen and total-tract fiber digestibility in dairy cows fed corn silages with different in vitro neutral detergent fiber digestibilities at 2 levels of dry matter intake

An in vivo study was performed to validate an in vitro procedure that predicts rate of fiber digestion and total-tract neutral detergent fiber digestibility (TTNDFD). Two corn silages that differed in fiber digestibility were used in this trial. The corn silage with lower fiber digestibility (LFDCS) had the TTNDFD prediction of 36.0% of total NDF, whereas TTNDFD for the corn silage with higher fiber digestibility (HFDCS) was 44.9% of total neutral detergent fiber (NDF). Two diets (1 with LFDCS and 1 with HFDCS) were formulated and analyzed using the in vitro assay to predict the TTNDFD and rumen potentially digestible NDF (pdNDF) digestion rate. Similar diets were fed to 8 ruminally cannulated, multiparous, high-producing dairy cows in 2 replicated 4×4 Latin squares with 21-d periods. A 2×2 factorial arrangement of treatments was used with main effects of intake (restricted to approximately 90% of ad libitum intake vs. ad libitum) and corn silage of different fiber digestibility. Treatments were restricted and ad libitum LFDCS as well as restricted and ad libitum HFDCS. The input and output values predicted from the in vitro model were compared with in vivo measurements. The pdNDF intake predicted by the in vitro model was similar to pdNDF intake observed in vivo. Also, the pdNDF digestion rate predicted in vitro was similar to what was observed in vivo. The in vitro method predicted TTNDFD of 50.2% for HFDCS and 42.9% for LFDCS as a percentage of total NDF in the diets, whereas the in vivo measurements of TTNDFD averaged 50.3 and 48.6% of total NDF for the HFDCS and LFDCS diets, respectively. The in vitro TTNDFD assay predicted total-tract NDF digestibility of HFDCS diets similar to the digestibility observed in vivo, but for LFDCS diets the assay underestimated the digestibility compared with in vivo. When the in vitro and in vivo measurements were compared without intake effect (ad libitum and restricted) considering only diet effect of silage fiber digestibility (HFDCS and LFDCS), no differences were observed between methods. These values suggest that our in vitro TTNDFD model could be used to predicted rate of fiber digestion and NDF digestibility for dairy cattle.

Dynamics of enzymatic digestion of elastic fibers and networks under tension

We study the enzymatic degradation of an elastic fiber under tension using an anisotropic random-walk model coupled with binding-unbinding reactions that weaken the fiber. The fiber is represented by a chain of elastic springs in series along which enzyme molecules can diffuse. Numerical simulations show that the fiber stiffness decreases exponentially with two distinct regimes. The time constant of the first regime decreases with increasing tension. Using a mean field calculation, we partition the time constant into geometrical, chemical and externally controllable factors, which is corroborated by the simulations. We incorporate the fiber model into a multiscale network model of the extracellular matrix and find that network effects do not mask the exponential decay of stiffness at the fiber level. To test these predictions, we measure the force relaxation of elastin sheets stretched to 20% uniaxial strain in the presence of elastase. The decay of force is exponential and the time constant is proportional to the inverse of enzyme concentration in agreement with model predictions. Furthermore, the fragment mass released into the bath during digestion is linearly related to enzyme concentration that is also borne out in the model. We conclude that in the complex extracellular matrix, feedback between the local rate of fiber digestion and the force the fiber carries acts to attenuate any spatial heterogeneity of digestion such that molecular processes manifest directly at the macroscale. Our findings can help better understand remodeling processes during development or in disease in which enzyme concentrations and/or mechanical forces become abnormal.

Effects of chemical composition variation on the dynamics of ruminal fermentation and biological value of corn milling (co)products

The objectives of this study were to evaluate the dynamics of gas production of several corn (co)products, to develop equations to predict the rate of ruminal fiber digestion, to estimate total digestible nutrients (TDN) and net energy for lactation (NEL), and to assess the stochasticity of chemical composition and nutritive value variability. Four corn milling (co)products were evaluated in this study: high protein dried distillers grains (HP-DDG), corn bran (BRAN) and dehydrated germ (GERM), and a dried distillers grains plus soluble produced with a low-heat drying process (BPX). Alfalfa hay was used as an internal standard feed in the in vitro fermentation dynamics analysis. Standard chemical analyses, in vitro digestibility, and in vitro gas production techniques were used to obtain the necessary physicochemical characterization of feeds. The in vitro dry matter digestibility at 24 and 48h of incubation decreased exponentially as acid detergent insoluble nitrogen increased. However, the degree of in vitro dry matter digestibility reduction was more accentuated at 24 than at 48h of incubation. The difference among these feeds regarding the dynamics of the anaerobic fermentation within different substrates (intact feed, and fiber and defatted residues) was evaluated. Results suggested that the proportion of fiber digested in the rumen was affected by the degree of sample processing and fat removal. Fractional fermentation rate (kf) of neutral detergent residue (without sodium sulfite) and defatted fiber residue for BRAN, GERM, HP-DDG, and BPX was estimated to be 0.0635 and 0.0852h−1, 0.0803 and 0.0914h−1, 0.118 and 0.117h−1, and 0.0695 and 0.0844h−1, respectively. The most influential variables affecting kfNDR of HP-DDG and BPX also affected the predicted TDN, suggesting that fiber quality is essential to ensure higher TDN values for these feeds. Our study indicated that it is possible to routinely quantify the rate of fiber digestion and this approach may be based on common analytical procedures namely estimates of neutral detergent fiber, acid detergent fiber, acid detergent insoluble nitrogen, ether extract, and acid detergent lignin. Our simulations of TDN values demonstrated that differences in fermentability and chemical composition of these corn (co)products might considerably affect the supply of energy to lactating dairy cow. The analytical methods developed in this study may serve as a valuable tool to assess nutrient quality and uniformity when samples differ in chemical composition.

Effects of feeding increased amounts of wet corn gluten feed on dairy cow metabolism and milk production (2009)

An experiment was conducted to evaluate the effects of feeding increasing dietary amounts of wet corn gluten feed (WCGF). Eight lactating Holstein cows were housed in a tie-stall facility and fed 1 of 4 diets containing 0, 11, 23, or 34% WCGF on a dry matter basis. To maintain similar nutrient concentrations, alfalfa hay, corn silage, corn grain, soybean meal, expeller soybean meal, and mineral supplements varied across diets. Feed intake, milk production, body weight, and body condition score were monitored, and effects of WCGF inclusion rate were assessed. Increasing the level of WCGF in the diet led to increased feed intake, milk production, and body condition. Concentrations of milk components did not differ among treatments; therefore, yield of energy-corrected milk and solids-corrected milk increased as well. In contrast, increasing dietary WCGF decreased efficiency of production and also decreased ruminal pH, possibly because treatments with greater proportions of WCGF had a decreased mean particle size. As expected, the decreased ruminal pH coincided with changes in ruminal volatile fatty acid concentrations. Furthermore, the rate of fiber digestion after 24 hours decreased when more WCGF was incorporated into diets. Results indicate that adding WCGF to dairy rations can increase energy-corrected milk yield, and this increase seems to be driven, at least in part, by an increase in feed intake.

Effect of types of non-fiber carbohydrate on in vitro forage fiber digestion of low-quality grass hay

Two in vitro experiments were conducted to study the effects of supplemental non-fiber carbohydrate (NFC) and fermentation pH on rate and extent of forage neutral detergent fiber (NDF) digestion by mixed ruminal microorganisms. A low-quality grass hay (53 g/kg CP and 761 g/kg NDF) that was finely ground served as the basal forage substrate. In Experiment 1, treatments were arranged as a 4 × 2 factorial in a randomized complete block design. The first factor consisted of supplemental NFC type: none (i.e., control, grass hay only), glucose, maltose, or soluble starch. The second factor was fermentation pH: adjusted (i.e., maintained at approximately pH 6.8) or non-adjusted (i.e., pH allowed to vary from an initial pH of 6.8 without interference). Treatments in Experiment 2 were arranged as a 4 × 2 factorial in a completely randomized design. The first factor consisted of supplemental NFC type: none (i.e., control, grass hay only), glucose, corn starch, and soluble starch. The second factor consisted of fermentation pH: adjusted or non-adjusted (the same as in Experiment 1). In both experiments NFC treatments were set such that the supplemental NFC supplied approximately 200 g/kg of the total substrate dry matter. In Experiment 1, an NFC type × pH interaction ( P < 0.01) was observed for extent of NDF digestion. The extent of NDF digestion was greater ( P < 0.01) when pH was adjusted, regardless of the NFC treatment. However, when pH was not adjusted, extent of NDF digestion was depressed ( P < 0.01) for treatments receiving supplemental NFC compared with the control. Rate of NDF digestion estimated by non-linear regression did not exhibit an NFC type × pH interaction ( P = 0.45). When compared with the control, rate of NDF digestion was depressed ( P < 0.01) regardless of pH treatment when supplemental NFC was provided. No significant differences were observed among the three sources of supplemental NFC with regard to either rate or extent of NDF digestion. In Experiment 2, an NFC type × pH interaction was observed ( P < 0.01) for extent of NDF digestion. In this experiment, no difference was observed among treatments for the extent of fiber digestion when pH was adjusted. However, similar to Experiment 1, when pH was not adjusted the extent of NDF digestion was depressed relative to the control when supplemental NFC was provided. Overall, rate of NDF digestion calculated from non-linear regression was depressed ( P < 0.01), regardless of pH treatment, in response to providing a supplemental source of NFC. However, the magnitude of depression was dependent ( P = 0.02) on the type of supplemental NFC included. In conclusion, our results indicate that avoiding the pH depression associated with NFC supplementation enables the maintenance of potential extent of digestion; however, the impact on rate of fiber digestion is not over-ridden by alleviating pH depression and is consistent with the existence of a “carbohydrate effect” on fiber digestion.

Methane emissions of differently fed dairy cows and corresponding methane and nitrogen emissions from their manure during storage.

This study investigated the effects of supplementing 40 g lauric acid (C12) kg(-1) dry matter (DM) in feed on methane emissions from early-lactating dairy cows and the associated effects on methane, nitrous oxide and ammonia release from the manure during storage. Stearic acid (C18), a fatty acid without assumed methane-suppressing potential in the digestive tract of ruminants, was added at 40 g kg(-1) DM to a control diet. The complete feed consisted of forage and concentrate in a ratio of 1.5:1 (DM basis). The manure was stored for 14 weeks either as complete slurry or, separately, as urine-rich slurry and farmyard manure representing two common storage systems. Methane release of the cows, as measured in respiratory chambers, was lower with C12 by about 20%, but this was mostly resulting from a reduced feed intake and, partly, from a lower rate of fibre digestion. As milk yield declined less than feed intake, methane emission per kg of milk was significantly lower with C12 (11.4 g) than with C18 (14.0 g). Faeces of C12-fed cows had a higher proportion of undigested fibre and accordingly methane release from their manure was higher compared with the manure obtained from the C18-fed cows. Overall, manure-derived methane accounted for 8.2% and 15.4% of total methane after 7 and 14 weeks of storage, respectively. The evolution of methane widely differed between manure types and dietary treatments, with a retarded onset of release in complete slurry particularly in the C12 treatment. Emissions of nitrous oxide were lower in the manures from the C12 treatment. This partially compensated for the higher methane release from the C12 manure with respect to the greenhouse gas potential. The total greenhouse gas potential (cow and manure together) accounted for 8.7 and 10.5 kg equivalents of CO2 cow(-1) d(-1) with C12 and C18, respectively. At unaffected urine-N proportion ammonia and total nitrogen losses from stored manure were lower with C12 than with C18 corresponding to the differences in feed and nitrogen intake. The present results suggest that manure storage significantly contributes to total methane emission from dairy husbandry, and that the identification of effective dietary mitigation strategies has to consider both the digestive tract of the animals and the corresponding manure.

Brown midrib sorghum in diets for lactating dairy cows.

In Experiment 1, 16 Holstein cows were assigned to one of four diets in replicated 4 x 4 Latin squares with 4-wk periods to measure dietary effect on short-term lactational performance. Additionally, 3 fistulated cows were assigned to the same diets in a 3 x 4 Youden square design with 4-wk periods to measure ruminal rate and extent of fiber digestion, fractional passage rate of fiber, ruminal pH, and concentration of volatile fatty acids. Diets comprised 65% of brown midrib (BMR) forage sorghum, standard forage sorghum, alfalfa or corn silages and 35% concentrate. Experiment 2 was conducted with 30 Holstein cows in early lactation to evaluate the same BMR sorghum hybrid in a 10-wk study with 35.3% standard sorghum, BMR sorghum, or corn silages as dietary treatments. Milk production was significantly higher for brown midrib than for standard sorghum in Experiment 1. Ruminal pH and acetate to propionate ratio did not differ among diets. The fractional passage rate of silage was not significantly different among the forages. In situ extent of ruminal fiber digestion was significantly higher for BMR than for standard sorghum, but rate of fiber digestion was not different. Similarly, in Experiment 2, in vitro extent of fiber digestion was significantly higher for BMR sorghum than for standard sorghum. Dry matter intake and body condition score were not significantly different between cows fed BMR and standard sorghum, but cows fed BMR sorghum resulted in long-term milk production greater than cows fed standard sorghum and similar to cows fed corn silage.

Fiber Digestion Dynamics of Sward Components within Switchgrass Populations

Forage quality as it relates to plant maturity is well established; however, strategies for improving fiber digestion in switchgrass populations have not been determined. The objectives of this study were to determine fiber digestion of sward components within switchgrass (Panicum virgatum L.) populations and which aspects of fiber digestion dynamics caused in vitro dry matter disappearance (IVDMD) differences of six switchgrass populations. This study was conducted in 1993 near Ames, IA, and Mead, NE. The experimental design was a randomized complete block design with a split-plot arrangement of treatments with four replicates at each location. Whole plots were populations and subplots were sward maturity. Trailblazer', 'Pathfinder', 'Cave-in-Rock', and three experimental switchgrass populations were used in this study. Populations were harvested on 9 June, 19 July, and 27 August at Ames and on 10 June, 27 July, and 26 August at Mead. Fiber composition and digestibility were determined on leaf blade, leaf sheath, and stem fractions of the primary growth stages. Significant differences for theoretical true digestibility (TD) and neutral detergent fiber (NDF) existed for morphological components at each sward maturity. However, digestion characteristics of the sward components were not stable across primary growth stages. Rate of fiber digestion was faster for most sward components at Ames than Mead, although stems of elongating tillers from elongating swards digested faster on plants grown at Mead than Ames. Rate of fiber digestion of stems was typically slower than either leaf blades or sheaths, but in several instances they were similar or stems had faster rates of fiber digestion. Although phenotypic selection can increase fiber digestibility, plant maturity remains an important factor, and selections may require evaluation at different stages of morphological development. Thus, improvements in forage digestion, at least in switchgrass, may only be manifested for the growth stage at which it was selected.

Associative effects between forages and grains: consequences for feed utilisation

Intake of metabolisable energy (ME) when forages and grains are fed together to ruminants may, due to digestive and metabolic interactions, be lower or higher than expected from feeding these components separately. These interactions, or associative effects, are due primarily to changes in the intake and/or the digestibility of the fibrous components of forage. Effects on voluntary forage intake (substitution effects) are usually much larger than on the digestibility of fibrous components, although the changes in forage intake may be a consequence of changes in the rate of digestion of the fibrous components. Positive associative effects, where grains increase voluntary intake and/or digestion of forage, are usually due to the provision of a limiting nutrient (eg. nitrogen, phosphorus) in the grain which is deficient in the forage. Negative associative effects, where grains decrease voluntary intake and/or digestion of forage, occur frequently and can cause low efficiency of utilisation of grain. Rate of substitution of grain for forage is related to forage intake, forage digestibility, the proportion of grain in the diet, and the maturity of the animal. Substitution rates are usually high in ruminants consuming high intakes of forage of high digestibility, probably due to the metabolic mechanisms which control voluntary intake reducing forage intake. Substitution rates are often low when animals are consuming forage of low to medium digestibility. Since voluntary intake of such forages is most likely determined by the capacity of the rumen to accommodate and pass to the lower gastrointestinal tract undigested forage residues, and of the rate of forage fibre digestion in the rumen, substitution is likely to be determined by changes in these processes. Reduced rate of fibre digestion in the rumen is often due to low rumen pH and/or an insufficiency of essential substrates for rumen microorganisms. Use of grains for lactating dairy cows involves an additional constraint since dietary grain may severely reduce milk fat content. Negative associative effects can be alleviated by ensuring supply of essential microbial substrates, feeding management, and modification of grain to minimise their adverse effects on fibre digestion, while ensuring satisfactory digestion of the grain and efficient microbial protein production.

Evaluation and Application of the Cornell Net Carbohydrate and Protein System for Dairy Cows Fed Diets Based on Pasture

This study evaluated the Cornell Net Carbohydrate and Protein System for dairy cows consuming diets based on pasture, assessed the sensitivity of the model to critical inputs, and demonstrated application opportunities. Data were obtained from four grazing experiments and four indoor pasture feeding experiments (25 dietary treatments) involving dairy cows in New Zealand and the US. The model provided a reasonably good estimate of changes in body condition score (r2 = 0.78; slope not significantly different from 1), estimated energy balance (r2 = 0.76; slope not significantly different from 1), blood urea N (r2 = 0.94; underprediction bias of 0.5%), microbial N flow (r2 = 0.88; slope not significantly different from 1), and milk production. The model underpredicted dry matter intake (r2 = 0.80; 13% bias) and overpredicted ruminal pH (r2 = 0.47; 1.7% bias). Predicted milk production was especially sensitive to changes in pasture lignin content, effective fiber, rate of fiber digestion, and amino acid composition of ruminal microbes. Milk production was first-limited by the supply of metabolizable energy when only high quality pasture was fed, but specific amino acids limited milk production when more than 20% of the diet consisted of a grain supplement. These results indicate that the Cornell Net Carbohydrate and Protein System can be used for dairy cows in a grazing system to make realistic predictions of performance.

Effects of Energy Source Addition on In vitro Digestioi Kinetics of Corn Stover Fiber

Harvatine, D.I., Cherney, D.J.R. and Cherney, J.H. 1998. Effects of energy source addition on in vitro digestion kinetics of corn stover fiber. J. Appl. Anim. Res., 13: 105–117. The effects of energy source addition on in vitro corn stover (Zea mays L.) neutral detergent fiber (NDF) digestibility were evaluated using eight corn stover populations varying in quality (66.76 to 74.33% NDF) and addition of glucose (25 or 50 mM) or ear corn (25 or 50%) during 48h digestion. Stover samples were supplemented with ear corn (35.5% NDF) as a fraction of initial corn stover sample weight (0–50% ear corn addition). Increasing levels of energy addition decreased the NDF digestibility of the stover fiber (P<0.01). Glucose, the more readily available energy source, had a greater impact on decreasing stover digestibility. When comparing six levels of corn addition (0 to 100%) using two stover populations, com addition beyond 25% significantly depressed NDF digestibility (P<0.05). Stover population affected the NDF digestibility of the sample (P<0.05). Increased corn addition resulted in decreased pH levels after 48h of digestion (P<0.01), which may account for decreased NDF digestibility. Two levels of corn addition (25 and 50% ear corn) and two stover populations were used to evaluate the effects of energy addition on fiber digestion kinetics over 96h digestion. The addition of ear corn did not significantly affect the lag time or rate of fiber digestion (P>0.05). Increasing the level of corn addition decreased the indigestible NDF residue, the potentially digestible fiber and the NDF digestibility of the sample (P<0.01). Results suggest that NDF digestibility of the whole plant may be a better evaluator of the nutritive value of com from a ruminant perspective than NDF digestibility of the stover.

Forage Quality Variation among Maize Inbreds: In Vitro Fiber Digestion Kinetics and Prediction with NIRS

The nutritive value of forage maize (Zea mays L.) may be improved through genetic selection for increased rate of fiber digestion or decreased indigestible fiber concentration. To identify sources of genetic variation, 45 maize inbreds were evaluated for in vitro neutral detergent fiber (NDF) digestion kinetic parameters using stem internode tissue harvested at silking during 2 yr. Near infrared reflectance spectroscopy (NIRS) was also used to estimate NDF digestion kinetic parameters. Maize inbreds varied significantly in NDF concentration and digestion kinetic parameters using either conventional in vitro analysis or NIRS predictions. Using NIRS predictions, inbreds varied in NDF concentration from 497 to 662 g kg−1 dry matter (DM), rate of NDF digestion ranged from 0.037 to 0.077 h−1, and extent of NDF digestion was 525 to 735 g kg−1 NDF. The ranges for NIRS predicted parameters were less than those observed for the calibration data set by conventional analysis. Correspondence between conventional analysis data and NIRS predictions were good, except for lag time. Digestion kinetics calculated from NIRS predicted residues provided more precise predictions of lag time and fractional rate of digestion when compared with observations derived from conventional analyses, than did direct prediction of these kinetic parameters. Correlations between rate of NDF digestion and 18‐h NDF digestibility (r = 0.79) or between potential extent of NDF digestion and 96‐h NDF digestibility (r = 0.95) were large enough that these two fermentation intervals might substitute for conducting complete digestion kinetic studies with eight to 10 fermentation times. The substantial genetic variation among these maize inbreds shows good potential for development of silage hybrids with improved fiber digestion parameters. Year and year × genotype interactions were significant suggesting that identification of superior inbred lines will require evaluations in multiple environments.

Effects of forage species and particle size on bacterial cellulolytic activity and colonization in situ

Two ruminally cannulated Holstein heifers were used to evaluate effects of three forage species and two particle sizes in a 3 x 2 factorial arrangement on in situ fiber disappearance and carboxymethylcellulase activity (CMCase). A second objective was to compare CMCase and 15N as relative bacterial colonization markers. At time zero, 15N-enriched ammonium sulfate was dosed into the rumen. Residues in nylon bags incubated for 3, 6, 9, 12, 18, 24, 30, 36, 42, 48, 60, and 72 h were analyzed for NDF, ADF, CMCase, and 15N. Rates of NDF and ADF disappearance were faster (P < .05) for red clover (RC) than for gamagrass (GG) or orchardgrass (OG) and for forages ground to pass a 2-mm screen (P < .05) than for those ground to pass a 5-mm screen. Cumulative area under the curve (AUC) of CMCase activity was related to both NDF disappearance (r2 = .93) and 15N AUC (r2 = .99), indicating that CMCase can be used to estimate relative colonization of cellulolytic particle-associated bacteria (PAB). During the first 18 h of incubation, RC had greater (P < .05) CMCase and 15N enrichment of in situ residues than did OG or GG. The RC residues also had a greater (P < .05) ratio of CMCase activity:15N enrichment; this was presumed to indicate that, during this time, RC supported a greater total PAB population and had a greater proportion of cellulolytic PAB than did either GG or OG. Differences in the colonization rate of forage particles by cellulolytic PAB relative to total PAB may account for differences in rate of fiber digestion.

In Vitro Digestion Kinetics and Quality of Perennial Grasses as Influenced by Forage Maturity

Objectives were to characterize changes in digestion kinetics of ‘Venture’ reed canarygrass (Phalaris arundinacea L.), ‘Regar’ meadow bromegrass (Bromus biebersteinii Roem & Schult.), ‘Garrison’ creeping foxtail (Alopecurus arundinaceus Poir.), ‘Fawn’ tall fescue (Festuca arundinacea Schreb.), and ‘Common’ timothy (Phleum pratense L.) with increased maturity. In 1991, three replicates each were harvested on four dates from early May to mid-June at Canton, Chazy, and Valatie, NY. Averaged over species and locations, NDF increased from 40.0 to 62.7%, indigestible fiber increased from 6.0 to 25.5%, lignin increased from 1.7 to 5.3%. and digestibility of fiber decreased from 79.7 to 44.2%. Lignin was highly correlated with fiber digestibility at all locations (r=−80, −.80, and −.76 for Canton, Chazy, and Valatie, respectively). Timothy was higher than all other species in lignin concentration at the first three stages. Rate of fiber digestion declined across harvest dates for all species (.0605 to .0396h−1 at Canton, .0654 to .0277h−1 at Chazy, and .0667 to .0287h−1 at Valatie); no species × harvest date interaction occurred at any location. Magnitude and speed of quality decline with maturity were more important than species differences in determination of digestion kinetics of perennial grasses. To ensure high quality forage, less emphasis should be placed on differences among grass species, and much more emphasis should be placed on harvest management.

Effects of ingestive and ruminative mastication on digestion of forage by cattle

The effects of chewing during eating and rumination on digestion of forage harvested in early and middle stages of maturity were studied. The experiment was conducted as a 4 × 4 Latin square using four Hereford yearling heifers. Heifers received once daily 5.45 kg of dry matter (DM) from: (1) alfalfa, 10% bloom; (2) alfalfa, 50% bloom; (3) orchardgrass, anthesis; (4) orchardgrass, post-anthesis. On a DM basis, crude protein and neutral detergent fibre (NDF) contents were: 21, 37%; 16, 47%; 17, 56%; and 14, 59% for the early, mid-bloom alfalfa, early and mature orchardgrass, respectively. Unmasticated forages, sampled using a hay corer, and masticated forages collected from the oesophageal fistula of each animal during periods of eating and rumination, were incubated in the rumen in sacco for predetermined intervals. Digestion of unmasticated alfalfa was initially rapid, whereas digestion of unmasticated orchardgrass was more gradual but continued over a longer period such that the extent of DM digestion in the rumen was greater ( P < 0.01) for grass compared with alfalfa. Potential DM digestibility of both forage species declined ( P < 0.01) with increased maturity. Potential DM digestibility of the forages was relatively high (more than 63%) and was increased ( P < 0.05) by 1.5–7.0 units by ingestive mastication. After ingestive mastication, the proportion of DM in the soluble fraction was increased relative to the slowly digestible fraction, but rate of digestion was not affected. The potentially digestible NDF fraction increased after chewing during eating, and lag time prior to the onset of fibre digestion decreased, but rate of fibre digestion was not altered. Digestion kinetics of ruminated digesta varied considerably among animals, and kinetics were altered minimally after chewing during a single rumination event. It was concluded that chewing during eating increases rumen degradation of forage by increasing the potentially digestible DM and NDF fractions and by decreasing the lag time for fibre digestion, but not by altering rate of digestion. Chewing during a single rumination event has minimal effects on digestion kinetics of ruminated digesta.

Evaluation of models to describe neutral detergent fibre digestion in cattle fed at two levels of dry matter intake

Potentially digestible fibre leaves the rumen either by enzymatic breakdown or by passage to the lower tract. The digestibility of potentially digestible fibre is a function of the rate at which fibre is digested and its retention time in the rumen. The procedures used for estimating the rate of fibre digestion (kd) and the rate of passage of feed particles (kp) are extremely variable. The estimates for kdand kpderived by using different procedures can have a large effect on the fibre digestibility calculated from kinetic parameters of fibre. The objective of the present study was to evaluate the different methods in estimating the kinetic parameters of mathematical models that will describe cell wall digestion in the rumen.

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.

The effect of a protein energy supplement on pasture protein and fibre digestion in the rumen of grazing steers

The effects of a protein-containing concentrate supplement on rumen environment, crude protein and fibre digestion and passage with two fresh forages were studied. The trial was designed as a crossover, with two treatments (T0, 0 kg supplement; T1, 3 kg supplement), two periods (17 days each) and six randomly distributed Aberdeen Angus steers. Animals grazed together with lactating Holstein cows. From 0900 to 1500 h they were on an oat pasture ( Avena sativa L.), while from 1630 to 0730 h they grazed a ryegrass ( Lolium perenne L.)-white clover ( Trifolium repens L.) pasture. There were no differences ( P > 0.05) between treatments and periods for rumen liquor pH (mean 5.93). Ammonia N concentration was higher ( P < 0.05) for T0 (16.36 mg dl −1) than for T1 (15.26 mg dl −1). Total VFA concentration (mean 193 mmol l −1), VFA proportion (C2, 44%; C3, 31%; C4, 17%) and C2 C3 ratio (mean 1.42) were not affected by treatments but showed variations during the day. Neither the rate of protein degradation nor the effective protein degradability showed differences ( P > 0.05) between treatments. The value of ryegrass-white clover pasture were 60 and 3% h −1, and for the oat pasture 72 and 3.5% h −1, respectively. Protein potentially digestible fraction was affected by treatments ( P < 0.05) in oat pasture (T0, 75.5%; T1, 73.4%), but not in ryegrass pasture (mean 61%). Readily available soluble protein fraction in ryegrass-white clover was higher ( P < 0.05) for T1 (16.6%) than for T0 (7.5%). Rye grass-white clover fibre potentially digestible fraction ( D o) was not different ( P > 0.05) between treatments and periods (mean 73%); lag time ( L) was different ( P < 0.05) between periods (I, 3.9 h; II, 0.4 h); rate of fibre digestion ( k d) was lower ( P < 0.05) for Period II (2.7% h −1) than Period I (3.7% h −1). In forage oat, concentrate significantly ( P < 0.05) reduced D o fraction from 82.4 to 79.4%, and increased k d (T0, 3.8% h −1; T1, 4.2% h −1). Differences between periods have also been observed. For the rye grass-white clover pasture actual extent of digestion (AED) was significantly higher ( P < 0.05) in Period I (41 vs. 35.1%). In forage oat there were differences in AED ( P < 0.05) for treatments (T0, 49.4%; T1, 41.5%) and periods (I, 54.7%; II, 43.9%). Rate of passage in reticulo-rumen (mean 2.6% h −1), caecum-proximal colon (mean 10% h −1) and small intestine transit times (mean 5.15 h) were not affected ( P < 0.05) by treatments and periods. The concentrate used affected rumen environment, protein and fibre digestion kinetics very little.

Fermentation of hammermilled barley, lupin, pea and faba bean grain in the rumen of dairy cows

Four lactating Friesian cows fitted with rumen cannulae were used in a 4 × 4 Latin square design experiment and fed on oaten hay ad libitum. Hammermilled lupin, pea, faba bean or barley grain, calculated to provide 70% of the total ration dry matter, was given twice daily via the rumen cannula. Rumen liquor was sampled at 0, 1, 2, 3, 4, 6, 8, 10 and 12 h after the grain was given at 08 00 h, and pH and the concentrations of ammonia-nitrogen, lactic, acetic, propionic and butyric acids measured. The rate of degradation of modified-acid-detergent fibre (MADF) was determined in milled oaten hay incubated in nylon bags in the rumen. When the cows were given hammermilled barley grain, rumen pH declined to a minimum value of 5.4, and from three to six hours after the grain was given rumen pH was significantly ( P < 0.05) lower than when the cows were given the legume grains. Rumen pH was maintained above 6.0 when the cows were given hammermilled lupin or faba bean grain. Rumen pH was generally reflected in rumen lactic acid concentration. Rumen ammonia-nitrogen concentration was significantly ( P < 0.05) higher at 0, 3, 4, 5, 6 and 8 h after the legume grains were given than after the barley grain. Differences between diets in the concentration of total volatile fatty acids and the proportions of volatile fatty acids were generally not significant. The rate of degradation of MADF in oaten hay tended to be less when the cows were given hammermilled barley or pea grain than when they were given lupin grain. Mean dry matter intake of oaten hay was significantly ( P < 0.05) higher when the cows were given the legume grains rather than the barley grain. It was concluded that giving high levels of hammermilled legume grains (especially lupins) rather than barley grain to dairy cows will result in rumen pH values and ammonia-nitrogen concentrations that are unlikely to cause significant depressions in the rate of fibre digestion or intake of cereal hay.