Neutral Detergent-soluble Carbohydrates Research Articles

Evaluation of different ratios of neutral detergent-soluble carbohydrate fractions on performance, ingestive behavior, and nitrogen balance in dairy goats.

Cell components soluble in neutral detergent are a diverse group, both compositionally and nutritionally. The present study aimed to evaluate production responses, behavior (eating, ruminating, and idling), and nitrogen balance of dairy goats fed different ratios of neutral detergent-soluble carbohydrate fractions. Five multiparous Alpine does with mean ± SD initial body mass of 49.5 ± 7.9kg and 60days of lactation were randomly assigned in a 5 × 5 Latin square design. The treatments were the ratios of starch (starch associated with soluble sugar [StSS]) to neutral detergent-soluble fiber (NDSF) (StSS:NDSF): 0.89, 1.05, 1.24, 1.73, and 2.92. No effect was observed (P > 0.05) of StSS:NDSF on the intakes of neutral detergent fiber (NDF) and NDSC. However, DM intake showed a quadratic behavior (P = 0.049). The ingestive behavior was affected by StSS:NDSF linearly increased (P = 0.002) the feeding efficiency. The increase in StSS:NDSF caused a linear increase in fecal (P = 0.011), urinary (P < 0.001), and milk nitrogen excretion (P = 0.024). The increase in StSS:NDSF affected (P = 0.048) milk yield and net energy lactation (P = 0.036). In conclusion, dairy goats experience reduced dry matter intake and milk yield when subjected to high-NDSC diets, specifically those above 1.24 StSS:NDSF ratio. Elevated NDSC levels in the diets lead to decreased feeding time, whereas rumination remains unaffected. Nitrogen losses in goats increase linearly with high-NDSC diets, and a significant impact on nitrogen balance.

Effects of Sprouted Barley with Different Cultivation Stages on Fermentation Characteristics and Degradation Kinetics in the Rumen

The present study investigated the effects of sprouted barley (SB) with different cultivation stages on fermentation characteristics and degradation kinetics in the rumen. The SB was cultivated in three different stages as follows: 0, 4, and 8 days. Dried samples from each cultivation stage of SB were incubated in the rumen buffer at 39 °C for 48 h in quadruplicate with three blanks. Dry matter (DM) and neutral detergent soluble carbohydrate concentrations of SB decreased linearly (p = 0.001) by increasing the cultivation stage, while crude protein, neutral detergent fiber (NDF), acid detergent fiber, and hemicellulose concentrations increased linearly (p ≤ 0.001). Total volatile fatty acid and butyrate in the rumen decreased linearly (p ≤ 0.020) by increasing the cultivation stage, while pH and propionate increased linearly (p &lt; 0.001). The total degradation fraction of DM and NDF increased quadratically (p ≤ 0.003). The fraction degradation rate of DM and NDF decreased linearly (p ≤ 0.001) by increasing the cultivation stage, while the lag phase increased linearly (p ≤ 0.010). The present study concluded that cultivated SB at 4 days was recommended for animal feed due to the highest nutrient degradation in the rumen without any adverse effects on fermentation characteristics.

Effect of neutral detergent-soluble carbohydrate profile on digestive parameters of dairy goats

ABSTRACTThe aim of the present study was to evaluate the effect of diets with high concentrations of different neutral detergent-soluble carbohydrates on the ruminal degradability and total digestibility, digestive parameters, and microbial efficiency of dairy goats. Five non-lactating goats and rumen and abomasum cannulas were arranged in a 5 × 5 Latin square design. The diets were the ratio between starch associated with soluble sugar (StSS) to NDSF (StSS:NDSF): 0.82; 1.3; 1.63; 2.94; and 5.35. Starch intake increased (P < 0.001) linearly with the increase of StSS:NDSF ratios in the diet. There was a linear decrease (P < 0.001) in the intake of soluble carbohydrates and neutral detergent soluble fiber (NDF). The ruminal degradability of dry matter (DM), crude protein, NDF, and NDSC decreased linearly (P < 0.05) with the increase of StSS:NDSF ratios in the diet. Total nitrogen flow, microbial nitrogen flow (MNF), and microbial efficiency increased (P < 0.05) with the increment of StSS:NDSF ratios in the diet. The increases in StSS:NDSF ratios in the diet affected only butyric (P < 0.001), valeric (P < 0.001), and isovaleric (P = 0.004) acids, as well as pH (P < 0.001). High StSS:NDSF ratio diets do not affect DM and NDF intake but reduce DM and NDF ruminal degradability, increasing MNF and, consequently, microbial efficiency in dairy goats.

Consumo, digestibilidade e balanço de nitrogênio de cordeiros alimentados com alto teor de amido ou fibra solúvel em detergente neutro associados ao óleo de girassol

The aim of this study was to evaluate the effect of different carbohydrate sources associated with sunflower oil on intake, digestibility of nutrients and nitrogen balance in diets of lambs. Twenty lambs were used, assigned in a completely randomized design with a 2 x 2 factorial arrangement of treatments with two sources of neutral detergent soluble carbohydrate, starch and neutral detergent soluble fiber, with and without the inclusion of 4.2% sunflower oil. The dry matter intake was not affected by carbohydrate sources and the inclusion of oil. Diets with a high percentage of starch provided higher digestibility of dry matter, starch and ether extract. The different sources of carbohydrates had no interference on digestibility of organic matter, crude protein, neutral detergent soluble fiber, nonfiber carbohydrates, neutral detergent fiber, hemicellulose and acid detergent fiber. The addition of oil in the diets increased the digestibility of ether extract. The combination of 4.2% oil in the diet high in soluble neutral detergent fiber had no influence on the nutrient digestibility, otherwise, the addition of oil at high starch diet caused a significant reduction in the digestibility of organic matter, neutral detergent fiber, hemicellulose and nonfiber carbohydrates. The quantities of nitrogen intake, absorbed and retained, did not differ as sources of carbohydrates and oil inclusion in the diet. The association of 4.2 % sunflower oil to the different sources of carbohydrates in the diet does not affect consumption and nitrogen metabolism in lambs. The addition of 4.2 % oil in the diet with high starch (28% of DM diet) promotes reduction in digestibility of organic matter, of fibrous and nonfibrous carbohydrate in the diet.

Effects of different sources of carbohydrates on intake, digestibility, chewing, and performance of Holstein dairy cows

To investigate the effects of different sources of carbohydrates on intake, digestibility, chewing, and performance, nine lactating Holstein dairy cows (day in milk= 100±21 d; body weight=645.7 ± 26.5 kg) were allotted to a 3 × 3 Latin square design at three 23-d periods. The three treatments included 34.91% (B), 18.87% (BC), and 18.86% (BB) barley that in treatment B was partially replaced with only corn or corn plus beet pulp in treatments BC and BB, respectively. The concentration of starch and neutral detergent soluble carbohydrate varied (22.2, 20.2, and 14.5; 13.6, 15.9, and 20.1% of DM in treatments B, BC, and BB, respectively). Cows in treatment BB showed a higher DMI and improved digestibility of DM, NDF, and EE compared with treatments B or BC. Ruminal pH was higher in cows fed on BB (6.83) compared with those that received B or BC treatments (6.62 and 6.73, respectively). A lower proportion of propionate accompanied the higher pH in the BB group; however, a greater proportion of acetate and acetate: propionate ratio was observed compared with cows fed either on the B or BC diet. Moreover, cows fed on the BB diet showed the lowest ruminal passage rate and longest ruminal and total retention time. Eating time did not differ among treatments, rumination time was greater among cows fed on the BB diet compared with the others, whereas total chewing activity was greater than those fed on BC, but similar to those fed on B. The treatments showed no effect on milk yield. Partially replacing barley with corn or beet pulp resulted in an increase in milk fat and a lower protein concentration. Changing dietary NFC with that of a different degradability thus altered intake, chewing activity, ruminal environment, retention time or passage rate, and lactation performance. The results of this study showed that beet pulp with a higher NDF and a detergent-soluble carbohydrate or pectin established a more consistent ruminal mat than barley and corn, thus resulting in higher mean retention time and chewing activity, whereas no changes in 3.5% FCM and milk fat were observed.

Eating a high fiber diet during pregnancy increases intake and digestibility of a high fiber diet by offspring in cattle

Experiences early in life influence preferences for the forages which animals eat as adults, but little is known about how such experiences affect forage intake and digestibility. We hypothesized that experience with high fiber (HF) diets in utero enables cattle to better utilize HF diets by enhancing intake and digestibility of HF diets. We exposed cows to either HF or low fiber (LF) diets from October 20 until parturition on March 15. The HF diet was primarily ammoniated wheat straw (AWS), while the LF diet was mainly grass hay (700g/kg orchardgrass and 300g/kg meadow bromegrass). The two diets were iso-net energy (NEm), isonitrogenous, and similar in mineral and vitamin contents, but they varied 10-fold in neutral detergent soluble carbohydrates. Following weaning, the 8mo old calves from mothers fed HF or LF diets during pregnancy were fed AWS and a high fiber supplement, and dry matter (DM) intake and digestibility were measured during the last half of a 40d experiment (i.e., 26d adaptation, 14d measured DM intake, 5d measured DM digestibility). Intake (5.6 versus 5.3kg/d; P=0.04) and digestibility (545 versus 523g/kg; P=0.03) of AWS were higher for calves fed HF than for those fed LF diets. As a result, digestible DM intake of AWS was higher for HF than LF (3.1 versus 2.8kg/d; P<0.01). Calves fed HF diets ate more straw as a proportion of their diet than did calves fed LF (733 versus 723g/kg; P=0.05). Total digestible DM intake (i.e., AWS+supplement) was higher for calves fed HF than LF diets (4.7 versus 4.4kg/d; P<0.01), as was total diet DM digestibility (613 versus 600g/kg; P=0.07). Calves were weighed at the conclusion of the DM intake and digestibility measurement periods, and then fed an AWS/processed wheat middlings diet for an addition 28d to determine daily gain. Collectively, increases in intake and digestibility affected body weight gains such that HF diet fed calves numerically gained more than LF fed calves even during this short period (0.45 versus 0.41kg/d; P=0.13). Higher DDM intake is likely important for pregnant cows and their offspring which winter for many months under extensive range conditions on dormant forages where their NEm requirements are marginally satisfied. These effects on offspring, further magnified by experiences with their mothers early in life, make cows and their progeny better adapted to using dormant forages during winter.

Kinetics fermentation and gas production of the neutral detergent-soluble fraction of fresh forage, silage and hay of Avena sativa

Neutral detergent treatment to evaluate the structural polysaccharides (NDF) removes soluble sugars, pectin substances, starch and the non-carbohydrate fraction (Van Soest, 1991). Despite the widely recognized importance of neutral detergent-soluble carbohydrates (NDS) in the early stages of forage digestion, little is known about their digestion kinetics because most in vitro methods have studied the disappearance of insoluble cell wall components. However, knowledge of the degradation characteristics of both fractions is very important to formulate balanced diets for high-yielding animals. Using the in vitro gas production system........

Carbohydrates in alfalfa-timothy mixtures predicted with near infrared reflectance spectroscopy equations developed for single species

Our objective was to evaluate the feasibility of using near infrared reflectance spectroscopy (NIRS) equations previously developed with a calibration set that included samples of both timothy and alfalfa to predict carbohydrate fractions in mixed samples of both species. Timothy and alfalfa mixed samples were prepared with the alfalfa proportion ranging from 0 to 100%, with increments of 4%. With previously developed NIRS equations based on samples of single species of timothy and alfalfa, concentrations of total ethanol soluble carbohydrates (TESC), starch, and neutral detergent soluble carbohydrates (NDSC) of the mixed samples were predicted successfully, but concentrations of organic acids (OA) and neutral detergent soluble fiber (NDSF) were unsuccessfully predicted. Adding 13 mixed samples to the initial calibration set of around 110 samples of pure timothy and alfalfa samples improved the accuracy of already successful predictions for TESC, starch, and NDSC, and resulted in a successful prediction for NDSF in timothy and alfalfa mixtures.Key words: Near infrared reflectance spectroscopy, sugars, Phleum pratense, Medicago sativa

Near-infrared reflectance spectroscopy prediction of neutral detergent-soluble carbohydrates in timothy and alfalfa

Carbohydrates in forage crops can be divided into neutral detergent-insoluble fiber and neutral detergent-soluble carbohydrates (NDSC); the latter includes organic acids (OA), total ethanol:water-soluble carbohydrates (TESC), starch, and neutral detergent-soluble fiber (NDSF). The accurate and efficient estimation of NDSC in forage crops is essential for improving the performance of dairy cattle. In the present study, visible and near-infrared reflectance spectroscopy (NIRS) were applied to evaluate the feasibility of predicting OA, TESC, starch, NDSF, NDSC, and all related constituents used to calculate these 5 carbohydrate fractions in timothy and alfalfa. Forage samples (n=1,008) of timothy and alfalfa were taken at the first and second harvests at 2 sites in 2007; samples were dried, ground, and then scanned (400 to 2,500nm) using an NIRSystems 6500 monochromator. A calibration (n=60) and a validation (n=15) set of samples were selected for each species and then chemically analyzed. Concentrations of TESC and NDSC in timothy, as well as starch in alfalfa, were successfully predicted, but many other carbohydrate fractions were not predicted accurately when calibrations were performed using single-species sample sets. Both sets of samples were combined to form new calibration (n=120) and validation (n=30) sets of alfalfa and timothy samples. Calibration and validation statistics for the combined sets of alfalfa and timothy samples indicated that TESC, starch, and NDSC were predicted successfully, with coefficients of determination of prediction (RP2) of 0.92, 0.89, and 0.93, and a ratio of prediction to deviation (RPD) of 3.3, 3.1, and 3.6, respectively. The NDSF prediction was classified as moderately successful RP2=0.88, RPD=2.8. The NIRS prediction of OA was unsuccessful RP2=0.38, RPD=1.3. All related constituents were predicted successfully RP2>0.90, RPD>3.0 by NIRS except ethanol-insoluble residual OM, with RP2=0.75 and RPD=1.9. Our results confirm the feasibility of using NIRS to predict NDSC, its fractions, and other related constituents, except for OA and ethanol-insoluble residual OM, in timothy and alfalfa forage samples.

Digestibility by Dairy Cows of Monosaccharide Constituents in Total Mixed Rations Containing Citrus Pulp

Ten lactating cows were divided into two groups and individually fed ad libitum one of two experimental total mixed rations (TMR) as follows: 1) a TMR containing 20% corn grain and 10% dry citrus pulp (high corn); and 2) a TMR containing 21% citrus pulp and 9% corn grain (high citrus pulp). Both TMR also contained corn silage (28%), legume haylage (19.5%), extruded full fat soybeans (13.5 to 14%), soybean meal (6.5%), and minerals and vitamins. Voluntary dry matter intake of cows consuming the high corn ration tended to be higher than for cows in the high citrus pulp group (22.2 vs. 20.7±1.0 kg/cow per day, respectively). Digestibility of NDF was higher for the TMR with high citrus pulp compared with the TMR with higher corn. Across treatments, neutral detergent fiber (NDF) glucose was more digestible than NDF xylose and uronic acids and less digestible than NDF arabinose, galactose, and mannose. Digestibility of total neutral detergent soluble carbohydrates was also higher in the high citrus pulp group (86.8, high citrus pulp vs. 80.3±1.7%, high corn); with glucose and uronic acids accounting for most of that difference. Consequently, higher total carbohydrate digestibility was obtained in the TMR containing higher citrus pulp compared with the TMR with a higher percentage of corn (77.1 and 72.5±1.0%, respectively). Slightly lower carbohydrate intake in cows fed higher citrus pulp was compensated by higher digestibility of carbohydrates and protein. Thereby, partial replacement of corn by citrus pulp in TMR of high producing dairy cows improved feed efficiency.

Effects of carbohydrates from citrus pulp and hominy feed on microbial fermentation in continuous culture.

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 < 0.05) for the hominy feed diet (14.2 mg/100 mL) than for the dried citrus pulp diet (9.3 mg/100 mL). Total N, nonammonia N, microbial N, and dietary N flows were not affected by treatments; however, the efficiency of microbial protein synthesis was greater (P = 0.055) for the dried citrus pulp diet than for the hominy feed diet (30.6 vs 27.8 g of bacterial N/kg of OM truly digested). Results from this experiment indicate that NDSF from citrus pulp can provide similar sources of energy compared with starch from hominy feed to support ruminal microbial growth.

Performance of Dairy Cattle Fed Citrus Pulp or Corn Products as Sources of Neutral Detergent-Soluble Carbohydrates

The effects of modifying the dietary profile of neutral detergent-soluble carbohydrates (NDSC) on milk production and rumen fermentation were determined. Corn silage and alfalfa hay-based diets were formulated to contain 40% calculated NDSC supplied primarily by dried citrus pulp as a source of neutral detergent-soluble fiber (NDSF), or corn products as sources of starch. Diets were compared within cow with reversal experiments with two periods. In experiment 1, 11 multiparous Holstein cows including three ruminally cannulated animals were individually fed diets containing 23.6% citrus pulp (diet CPD) or 25.3% corn hominy (diet HD) on a dry matter basis. In experiment 2, 184 animals fed as two groups received diets containing 20.5% citrus pulp (diet CPD) or 19.5% cornmeal (diet CMD). Diets CPD provided more dietary NDSF and HD and CMD more starch. In experiment 1, cows fed HD had a greater milk protein percentage (+0.12%), and tended to yield more milk protein (0.08kg/d) than cows fed CPD. Although ruminal H+ concentrations did not differ between diets, diet × time postfeeding interactions were significant. Ruminal organic acid concentrations did not differ between diets. In experiment 2, cows fed CMD yielded more milk (3.9kg/d), 3.5% fat- and protein-corrected milk (2.6kg/d), fat (0.05kg/d), and protein (0.08kg/d), whereas cows fed CPD produced greater concentrations of fat (+0.18%), and milk urea nitrogen (0.76mg/dl). Modifying the proportions of NDSC in the diet can alter milk production and composition, the pattern of ruminal fermentation, and N utilization in dairy cows.

A method for partitioning neutral detergent-soluble carbohydrates

A method was developed to fractionate the neutral detergent-soluble carbohydrates (NDSC) in feedstuffs. Differential solubilities of carbohydrates in 80:20 (v/v) ethanol/water were used to partition NDSC into organic acids (OA) and mono- and oligosaccharides soluble in ethanol/water from starch and neutral detergent-soluble fibre (NDSF) which are insoluble. Mono- and oligosaccharides (total ethanol/water-soluble carbohydrate) were measured on the ethanol/water extract, and starch was measured on the ethanol/water-insoluble residue. The OA and NDSF, the two most compositionally diverse NDSC fractions, were estimated by difference. The method allows partitioning of the NDSC on a nutritionally relevant basis into (1) organic acids, (2) total ethanol/water-soluble carbohydrate, (3) starch and (4) neutral detergent-soluble fibre. The methods involved in this fractionation are relatively simple or are commonly used. © 1999 Society of Chemical Industry

A method for partitioning neutral detergent‐soluble carbohydrates

A method was developed to fractionate the neutral detergent-soluble carbohydrates (NDSC) in feedstuffs. Differential solubilities of carbohydrates in 80:20 (v/v) ethanol/water were used to partition NDSC into organic acids (OA) and mono- and oligosaccharides soluble in ethanol/water from starch and neutral detergent-soluble fibre (NDSF) which are insoluble. Mono- and oligosaccharides (total ethanol/water-soluble carbohydrate) were measured on the ethanol/water extract, and starch was measured on the ethanol/water-insoluble residue. The OA and NDSF, the two most compositionally diverse NDSC fractions, were estimated by difference. The method allows partitioning of the NDSC on a nutritionally relevant basis into (1) organic acids, (2) total ethanol/water-soluble carbohydrate, (3) starch and (4) neutral detergent-soluble fibre. The methods involved in this fractionation are relatively simple or are commonly used. © 1999 Society of Chemical Industry

Kinetic parameters of ruminal degradation estimated with a non-automated system to measure gas production

The kinetic parameters of the dry matter and neutral detergent fiber degradation of some tropical forages were estimated through anaerobic incubations by the cumulative gas production technique and by curve subtraction. The measurements were made using a non-automated system, which has a manometer connected to a syringe. Corn silage and the forages Cynodon dactylon, Pennisetum purpureum, Brachiaria brizantha, Brachiaria decumbens, and Melinis minutiflora were studied. The kinetic interpretations of the cumulative gas production data were analysed by using a multicompartmental logistic model. The data obtained with this system showed lowest coefficient of variation for both dry matter (DM) and neutral detergent fiber (NDF), especially after 12 h of incubation, being similar to those described in other studies with automated systems. A strong linear relationship was observed when the total of gas produced was plotted against the NDF degradation, the amount of neutral detergent soluble carbohydrate and the effective degradability of the forages studied. It was concluded that kinetic parameters of the rapid and slow fractions in the feed constituents could be estimated accurately by cumulative gas production measured with this cheaper non-automated system.

Apparent ileal and total-tract nutrient digestion by pigs as affected by dietary nondigestible oligosaccharides.

The effects of two types of nondigestible oligosaccharides (NDO), fructooligosaccharides (FOS), and transgalactooligosaccharides (TOS) were studied on growing and weanling pigs' nutrient digestion. Dietary NDO were included at the expense of purified cellulose. Twenty-five 57-d-old growing pigs, averaging 15.9+/-.6 kg on d 0 of the experiment, were fed a corn-based control diet or the control with 6.8 or 13.5 g of FOS/kg or 4.0 or 8.0 g of TOS/kg (five pigs per diet). Feces were collected on d 28 to 32, and small-intestinal digesta were collected (slaughter technique) on d 42 to 47 of the experiment. Feeds, feces, and digesta were analyzed for DM, inorganic matter, CP, ether extract, and crude fiber. Dietary NDO did not significantly affect apparent fecal and small intestinal digestion of nutrients in growing pigs. After being fed a NDO-free diet through d 10 after weaning, 38-d-old weanling pigs (n = 20), averaging 10.4+/-.8 kg on d 0 of the experiment, were fed a control diet (based on cornstarch, casein, and oat husk meal) or the control with 10 or 40 g of FOS or TOS/kg (four pigs per diet). Feces and urine were collected on d 13 to 17, and ileal digesta were collected via a postvalve T-cecum cannula on d 33 to 37 of the experiment. Feeds, feces, and digesta were analyzed for DM, inorganic matter, CP, ether extract, starch, NDF, ADF, ADL, Ca, P, Mg, Fe, Cu, and Zn. Nonstarch neutral-detergent soluble carbohydrates (NNSC) completed the mass balance for the carbohydrates. Urine was analyzed for N and minerals. The apparent fecal digestion of NNSC increased in the NDO-supplemented diets. The TOS-fed pigs tended (P<.10) to have a higher apparent fecal digestion of CP than the FOS-fed and control pigs but excreted more N via the urine (P<.01). Nitrogen and mineral balances were not affected. The FOS was nearly completely degraded prececally. Mean fiber digestion was lower at the fecal compared with the ileal level, as was the extent of NDO effects. This indicates that fiber digestion requires more than 2 wk to adapt to dietary NDO. Apparent ileal digestion of hemicellulose increased for the NDO-supplemented diets (P<.05), but that of NNSC decreased (P<.001). Thus, under the well-controlled conditions of this experiment, dietary NDO hardly affected nutrient digestion in well-kept growing and weanling pigs. However, digestion of dietary nonstarch carbohydrates may be affected.

Measurement and kinetic analysis of the neutral detergent-soluble carbohydrate fraction of legumes and grasses

The fermentation of the neutral detergent-soluble (NDS) fraction of two legumes (clover, alfalfa) and two grasses (timothy, guinea grass) was measured using a curve subtraction technique with in vitro gas production data from the whole forage and the isolated neutral detergent-extracted fiber. The NDF disappearance and VFA production also were measured. There were no significant differences between the VFA patterns from whole forage and NDF. There was a good linear correlation between the volume of gas produced and the mass of fiber digested in the NDF samples. Analysis of the gas curves with a dual-pool logistic model gave a lag value, digestion rates and pool sizes for the whole forage, the fiber component, and the NDS fraction. Rates for the NDS fraction ranged from .152 h-1 for clover to .191 h-1 for timothy. These rates are appreciably lower than values assumed in some models. Application of a triple-pool logistic model revealed the presence of faster-digesting material in the legumes. We discuss several different ways to measure the NDS pool size. The simplest method requires only a single gas measurement at the end of in vitro digestion of the whole forage coupled with an NDF disappearance measurement. The curve subtraction technique can provide information on the size and digestion kinetics of the NDS pool. This information is useful both for model studies and for agronomic research and may help us to understand the nutritional significance of this fast-digesting carbohydrate fraction.

Monosaccharide Digestibility by Dairy Cows Fed Diets High in Concentrate and Containing Alfalfa Silages

Alfalfa was ensiled by the conventional wilting process or as a mixture of 70% fresh alfalfa plus 30% wheat straw treated with SO2. The effects of these silages on the digestibility of monosaccharide constituents of the TMR by dairy cows was examined. Ten cows in early lactation were divided into two groups of 5 that had similar performance data at the onset of the experiment. Cows were fed for ad libitum intake for 28 d a TMR composed of 70% concentrates, 15% alfalfa hay, and 15% silage. The alfalfa silage had lower glucose, xylose, and total carbohydrates than the silage of alfalfa plus wheat straw treated with SO2. Digestibilities of DM (70 to 71%), OM (72%), and total carbohydrate (83%) were similar in the two TMR. The digestibilities of NDF carbohydrate for both TMR were similar. Regardless of treatment, NDF glucose was more digestible than NDF xylose and NDF uronic acid and less digestible than NDF arabinose, galactose, and mannose. The digestibility of total neutral detergent-soluble carbohydrates was 89% in both TMR, but those of neutral detergent-soluble xylose, mannose, and galactose were lower than those of neutral detergent-soluble glucose, arabinose, and pectin.