Passage Kinetics Research Articles

Ruminal passage rate and digestibility of fiber from dairy cows consuming diets containing alfalfa and orchardgrass hays with different concentrations of undegradable neutral detergent fiber (uNDF)

This study aimed to evaluate the effect of feeding diets with different fractions of undegraded NDF (uNDF) and potentially degradable (pdNDF) on ruminal NDF degradation and passage kinetics of lactating dairy cows. Six rumen-cannulated (533 ± 43 kg BW and 122 ± 15 DIM) and 6 non-cannulated (558 ± 62 kg BW and 126 ± 16 DIM) primiparous Holstein dairy cows were randomly assigned to 1 of 2 experimental diets in a crossover design with 2 28-d periods. The experimental diets were formulated to include either alfalfa hay (ALFA) or orchardgrass hay (ORCH) in addition to corn silage. Rations were formulated to contain 30% NDF (DM basis), where the concentrate, corn silage, and each of the hays provided one third of the dietary NDF. The marker dilution technique was used to measure the passage rate utilizing a pulse dose of marked corn silage fiber. On d 17 and 24 of each period, ruminal contents were evacuated to determine ruminal pool size. Following the return of the ruminal contents containing the pulse dose of marked corn silage to the rumen, ruminal grab samples were collected at 0, 3, 6, 9, 12, 24, 36, 48, 60, and 72 h. Samples from each time point were separated into solids and liquid, and the solids were analyzed for NDF, uNDF, and marker concentration. Alfalfa hay had a higher concentration of CP (16.4 vs. 10.7%) and a lower concentration of NDF (38.0 vs. 63.2) than orchardgrass hay. Alfalfa hay had a greater concentration of uNDF than orchardgrass hay (36.5 vs. 32.8% uNDF; NDF basis). Cows consuming the ALFA diet had similar milk yield (39.1 kg/d) and similar milk fat and protein concentrations (3.72% fat and 3.24% protein, respectively) than cows consuming the ORCH diet. Cows consuming the ALFA diet consumed more DM (26.7 vs. 24.6 kg/d) and uNDF (2.7 vs. 2.3 kg/d), than cows consuming the ORCH diet. Cows consuming the ALFA diet digested more NDF and pdNDF than cows consuming the ORCH diet (3.3 vs. 2.8 kg/d). Even though cows consuming the ALFA diet had a smaller pool size of NDF than cows consuming the ORCH diet (5.4 vs. 6.7 kg), the pool size of uNDF did not differ between groups (2.4 kg). Cows consuming the ALFA diet had a faster rate of passage of uNDF than cows consuming the ORCH diet (5.02 vs. 4.03%/h). This translated into a shorter mean retention time of uNDF for cows consuming the ALFA diet relative to cows consuming the ORCH diet (21.0 vs. 26.2 h). In conclusion, cows consuming diets containing alfalfa hay had a faster ruminal passage rate and a shorter mean retention time of uNDF than cows consuming diets containing orchardgrass hay, and this occurred despite the greater concentrations of dietary uNDF in the alfalfa-based diet. These findings suggest that the kinetics of ruminal digestion and passage influence NDF degradation in ways beyond uNDF concentration or forage quality.

Passage and degradation kinetics of solid particles from agricultural residues

The use of waste generated in the agroindustry can result in increased production at a relatively low cost compared to traditional ingredients, especially for producers with easy access to this waste. This study proposes to estimate the kinetics of passage and degradation of corn, soybean, wheat residues and corn silage in the gastrointestinal tract of cattle. Four rumen-fistulated animals with an average weight of 450 ± 50 kg were assigned to four treatments (corn, soybean, wheat residues and corn silage) in a 4×4 Latin square experimental design. The fiber from the residues and corn silage used to estimate the passage kinetics was marked with potassium dichromate, whereas the in situ technique was employed to estimate the fiber degradation kinetics. A larger potentially degradable fraction and a smaller undegradable fraction were observed for corn residue and corn silage, whereas no differences were detected between the materials for passage kinetics. The residue from corn processing is similar to corn silage in terms of degradation kinetics and mean fiber retention time, while the other residues have worse degradation kinetics than corn, which is due mainly to the elevated undegradable fraction. All the analyzed residues, as well as corn silage, share the same characteristics of fiber passage kinetics.

Açai seed as a fiber source in high-concentrate beef cattle diets and its nutritional effects

This study evaluated the effects of different levels of inclusion of coarsely broken açai seed (CBAS) in the diet of feedlot beef cattle on the intake, digestibility, ruminal degradation, passage kinetics, and nitrogen utilization efficiency. Five ruminally fistulated crossbred bulls (387±27kg body weight) were used in a 5×5 Latin square design. A total mixed ration with 750g/kg concentrate and 250g/kg roughage, based on the total dry matter (DM), was used. The treatments consisted of the inclusion of CBAS at 0, 50, 100, 150, and 200g/kg DM as a fiber source in the diet. The roughage used was Mombasa grass silage, which was partially replaced by CBAS. A linear increase in organic matter (OM; P=0.042), crude protein (CP; P=0.023), and neutral detergent fiber (NDF; P=0.022) intake was observed with the inclusion of CBAS in the diet, while a linearly increasing trend was observed for DM (P=0.077) and metabolizable energy (ME; P=0.051) intake. The total, ruminal, and intestinal digestibility of DM and nutrients were not affected by the inclusion of CBAS (P > 0.10). Ruminal ammonia nitrogen decreased linearly (P=0.045), while acetate concentration showed a linear increase (P=0.038), propionate was not affected (P=0.762), and butyrate showed a linear tendency to increase (P=0.086) with the inclusion of CBAS. Passage rate and DM degradation, as well as N utilization were not affected by the inclusion of CBAS (P > 0.10), except for N fecal excretion that showed a linear tendency to increase (P=0.092). Thus, we conclude that CBAS increases organic matter, crude protein, metabolizable energy, and neutral detergent fiber intake in high-concentrate diets without compromising rumen kinetics and nitrogen utilization in beef cattle. Therefore, the CBAS can be considered as an alternative roughage source in scenarios where forage silage of low quality is the fiber source.

Fluid and particle retention in a small New World and a small Old World cervid, the southern pudu (Pudu puda) and Reeves's muntjac (Muntiacus reevesi)

Ruminants differ in the pattern how small particles and liquids pass through their gastrointestinal tract, and in particular their reticulorumen (RR). Based on that they may be classified into ‘moose-type’ and ‘cattle-type’ species (smaller and larger differences between particle and liquid passage, respectively). The ratio between the retention of particles and fluids is called the ‘selectivity factor’ (SF) and is a species-specific characteristic, studied in tragulids, giraffids and bovids, but not in many cervid species. Recently, it has been suggested that a high SF might also serve to wash digesta clean of external abrasives prior to regurgitation for rumination. In this study, we measured SF and passage kinetics (using a liquid marker and markers of different particle size, fed with the diet) in a capreoline deer, the southern pudu (Pudu puda, n = 5, 10.3 ± 2.9 kg, kept at two zoos) and a cervine deer, the Reeves's muntjac (Muntiacus reevesi, n = 6, 11.0 ± 1.7 kg, kept at a research facility). The relative daily dry matter intake (38 ± 3 g/kg0.75 for pudu and 76 ± 5 g/kg0.75 for muntjac) was higher, and the mean retention times (MRT) correspondingly shorter (e.g., MRT small particles in the total digestive tract 39 ± 8 h for pudu and 15 ± 2 h for muntjac), in the muntjac. The SF for small particles/liquid in the reticulorumen were, however, similar for both species, at 1.47 ± 0.21 for pudu and 1.66 ± 0.20 for muntjac, indicating a ‘moose-type’ physiology for both, irrespective of their different phylogenetic origin. To date, SF recorded in bovids attain distinctively higher values than the few reported for cervids. This situation reflects the degree of hypsodonty (tooth crown height) attained by these taxa, which is higher in bovids than in cervids. Together, constraints in hypsodonty as well as SF might limit cervids to more mesic habitats without distinct loads of external abrasives (such as dust or grit) on their food. In both species, some animals showed the typical ruminant pattern of a longer MRT for large than for small particle markers, but in some animals, this difference was not evident. This may be due to variable degrees of marker chewing during ingestion.

Influence of Anti-Coccidial Compounds and Phytogenic Saponin Extracts on In Vitro and In Vivo Ruminal Fermentation and Methane Production of Cattle.

Four experiments were conducted to evaluate sources of anti-coccidial compounds and phytogenic saponin extracts on in vitro and in vivo ruminal fermentation and CH4 production at multiple inclusion levels. In experiment 1, eight steers were fed either a finishing diet or a finishing diet supplemented with 0.5 mg/kg BW decoquinate (DCQ) and 3.33 mg/kg BW Yucca schidigera extract (YSE), and respiratory gas exchange was measured. In experiment 2, four ruminally-cannulated steers were fed the same treatments as experiment 1, and ruminal fermentation was evaluated. Anti-coccidial sources (experiment 3; monensin, DCQ, amprolium) and saponin sources (experiment 4; YSE, Quillaja saponaria extract) and levels were evaluated for effects on in vitro ruminal fermentation and CH4 production. DCQ + YSE supplementation did not influence (p ≥ 0.24) in vivo respiratory gas consumption/production, in situ DM degradation, or liquid passage kinetics. Ruminal propionate proportion tended to increase (p = 0.09) with DCQ + YSE. Monensin decreased (p ≤ 0.04) in vitro acetate:propionate and CH4 production; saponin supplementation linearly increased (p < 0.01) propionate proportion but did not influence (p ≥ 0.38) in vitro CH4 production. Saponins and non-antibiotic anti-coccidials did not influence in vitro or in vivo CH4 production with finishing diets.

Effect of solid feed level and types of roughage on passage kinetics of milk replacer, concentrate, and roughage in veal calves

This study aimed (1) to provide estimates of total mean retention times of milk replacer (MR), concentrates, and roughage in veal calves fed a mixed diet; (2) to determine the effect of level and type of solid feed (SF) on passage kinetics of MR, concentrates, and roughages in veal calves; and (3) to compare passage kinetics in veal calves using the fecal excretion curves of indigestible markers and a noninvasive 13C tracer breath test approach to determine whether the latter technique can serve as an alternative. At the start of the trial, 48 Holstein-Friesian calves (6 wk of age; 68 ± 7.7 kg of body weight; BW) were assigned to 1 of 4 dietary treatments (for statistical analysis, only 39 calf observations were used). Three treatments contained chopped wheat straw as roughage in the SF mixture in a concentrate:roughage ratio of 90:10 (dry matter basis). The SF level was 20 g/kg of metabolic BW per day (low straw), 30 g/kg of metabolic BW per day (middle straw), or 40 g/kg of metabolic BW per day (high straw). The fourth treatment (high hay) contained long perennial ryegrass hay as roughage in the SF mixture in a concentrate:roughage ratio of 70:30 (dry matter basis, at 40 g/kg of metabolic BW per day). The quantity of MR was fixed for the high straw treatment, whereas the amount of MR for the other treatments during the adaptation period was adjusted based on a pair gain strategy (i.e., exchanging ration components but keeping similar net energy). At the end of the adaptation period, calves ranged from 12 to 15 wk of age with an average BW of 123 ± 8.6 kg. Passage kinetics of concentrates were estimated by measuring 13C enrichment excess of CO2 in breath from a pulsed-dose of [1-13C]octanoate. Passage kinetics of roughage, concentrates, and MR were also estimated using fecal excretion curves obtained after ingestion of chromium-mordanted roughage, Yb2O3, and Co-EDTA, respectively. We conclude that [1-13C]octanoate cannot serve as a measure for oro-duodenal transit of concentrates because of unrealistic estimates. Based on the fecal excretion curves, we concluded that the total mean retention time of MR (i.e., time to peak; the moment that the excretion curve reaches peak concentration) was, on average, 12.4 h, and that the passage kinetics of MR was not affected by the level or type of SF. The mean retention time of concentrates was shorter (21.4 h) than that of both straw (59.1 h) and hay (36.8 h), and was not affected by the level or type of SF. Also, the mean retention time of the slowest compartment (i.e., the rumen) was shorter for concentrates (39.6 h) than that of straw (110.0 h) and hay (59.2 h). Contrary, the passage of roughage was affected by level and type of SF. Long hay increased time to peak by 22.3 h and decreased ruminal mean retention time by 50.8 h relative to chopped straw, indicating that the passage rate of long hay is faster than that of chopped straw. We conclude that the level and type of SF only affects the passage kinetics of roughage and not that of MR and concentrates.

Effects of soybean meal supplementation on ruminal kinetics of feed particle size reduction and passage in dairy cows fed rice straw.

Six ruminal-cannulated nonlactating Holstein Friesian cows (mean body weight:660 ± 42.9 kg) were used to investigate the effect of soybean meal (SBM) supplementation on voluntary rice straw (RS) intake, feed particle size reduction, and passage kinetics in the rumen. They were allocated to two dietary treatments: RS alone or RS supplemented with SBM. Voluntary dry matter intake of RS and total tract fiber digestibility was increased by SBM supplementation (p < 0.05). Supplementation with SBM decreased rumination time per dietary dry matter (DM) and neutral detergent fiber (NDFom) intake (p < 0.01). Particle size distribution in the rumen and total ruminal NDFom digesta weights were not affected by SBM supplementation. However, the disappearance rates of total digesta and large and small particles from the rumen were increased by SBM supplementation (p < 0.01). Moreover, SBM supplementation increased the rate of size reduction in ruminal particles (p < 0.05). In situ disappearance of DM and NDFom of RS in the rumen was greater in SBM-supplemented cows than in nonsupplemented cows (p < 0.05). This study clearly showed that increased ruminal RS particle size reduction, passage, and fermentation due to SBM supplementation accelerated the RS particle clearance from the rumen and resulted in increased voluntary RS intake of dairy cows.

Bile acid-retention by native and modified oat and barley β-glucan

Foods rich in cereal β-glucan are efficient dietary tools to help reduce serum cholesterol levels and hence the risk of cardiovascular diseases. However, β-glucan undergoes various reactions during food processing, which alter its viscous properties and interactions with components of the gastrointestinal tract. It has been proposed in the literature that oxidation and partial hydrolysis increase β-glucan’s bile acid-binding activity, and therefore its effectiveness in lowering cholesterol. Here, the passage kinetics of a bile salt mix across a dialysis membrane was studied with or without oat and barley β-glucan extracts, native or modified (partial hydrolysis and oxidations by sodium periodate or TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)). Bile acid-retention turned out to be purely a function of viscosity, with the most viscous native extracts exhibiting the strongest retardation of bile acid permeation. Opposite of what was suggested in the literature, oxidation and molecular weight reduction do not seem to increase the bile acid-binding capability of β-glucan.

Increased diet viscosity by oat β-glucans decreases the passage rate of liquids in the stomach and affects digesta physicochemical properties in growing pigs

Rheological properties of digesta play a role in digesta passage kinetics through the gastrointestinal tract, in turn affecting nutrient absorption kinetics. Therefore, we studied the effects of diet viscosity on digesta passage and physicochemical properties in pigs. Twenty male growing pigs (35 kg body weight at the start) were assigned to one of five diets with increasing dietary concentrations of β-glucans (BG; from 0 % to 10 %), in exchange for maize starch. After a 17-day adaptation period, pigs were euthanised and the mean retention time (MRT) of digesta solids (TiO2) and liquids (Cr-EDTA) in the stomach, and proximal and distal half of the small intestine was quantified. In the stomach, the MRT of liquids, but not of solids, increased when dietary BG level increased (6 min per % dietary BG, P = 0.008 and R2 = 0.35). Concomitantly, stomach DM content (5 g/kg per % dietary BG, P < 0.001 and R2 = 0.53) and apparent digesta viscosity (56 Pa × s at 1/s shear rate per % dietary BG, P = 0.003 and R2 = 0.41) decreased. In the proximal half of the small intestine, no effects of dietary BG level were observed. In the distal half of the small intestine, water-binding capacity (WBC) of digesta increased (0.11 g/g digesta DM per % dietary BG, P = 0.028 and R2 = 0.24) and starch digestibility decreased (0.3% per % dietary BG, P = 0.034 and R2 = 0.23) when dietary BG level increased. In the colon, apparent digesta viscosity at 45/s shear rate increased (0.1 Pa × s per % dietary BG, P = 0.03 and R2 = 0.24) in the proximal half of the colon, and digesta WBC increased (0.06 g/g digesta DM per % dietary BG, P = 0.024 and R2 = 0.26) in the distal half of the colon when dietary BG level increased. To conclude, increasing dietary BG level caused the MRT of liquids, but not that of solids, to increase in the stomach, resulting in reduced separation of the solid and liquid digesta fractions. This caused dilution of the stomach content and reduction in digesta viscosity when dietary BG levels increased. Effects of dietary BG level on physicochemical properties in the proximal small intestine were absent and may have been due to a low DM content. The WBC of digesta in the distal small intestine and colon increased when dietary BG level increased, as did apparent digesta viscosity in the proximal colon. This likely reflects the concentration of BG in digesta when moving through the gastrointestinal tract.

Digestibility and Retention Time of Coastal Bermudagrass (Cynodon dactylon) Hay by Horses.

Simple SummaryLonger retention of forages with increased fiber concentrations may be a compensatory digestive strategy in horses. We investigated the digestive characteristics of bermudagrass hay, a prominent warm-season grass in the southeast United States that has greater fiber concentrations than other common forages fed to horses. The morphological structure and photosynthetic pathway of warm-season grasses differ from cool-season grasses and legumes which may have important impacts on equine digestion and digesta transit through the gastrointestinal tract. The retention time of Coastal bermudagrass was longer than alfalfa or orchardgrass hay. The digestibility of Coastal bermudagrass decreased with increasing maturity, but the fiber digestibility of alfalfa and orchardgrass was similar to the earliest maturity of Coastal bermudagrass hay. The chemical composition of the plant cell wall influences diet digestibility and is a major difference between warm-season and cool-season forages. The increased retention time of Coastal bermudagrass allows for microbial fermentation to occur longer, adapting to more difficult-to-digest plant cell walls in warm-season forages. The decrease in diet digestibility when horses consume warm-season forages can be reduced by feeding early maturity forage, by harvesting hay at an earlier stage of growth or managing pastures in a vegetative state.Bermudagrass (Cynodon dactylon) and other warm-season grasses are known for their increased fiber concentrations and reduced digestibility relative to cool-season grasses and legumes. This study investigated the digestive characteristics and passage kinetics of three maturities of Coastal bermudagrass hay. A 5 × 5 Latin square design experiment was used to compare the digestion of five hays: alfalfa (Medicago sativa, ALF), orchardgrass (Dactylis glomerata, ORCH), and Coastal bermudagrass harvested at 4 (CB 4), 6 (CB 6), and 8 weeks of regrowth (CB 8). Horses were fed cobalt-ethylenediaminetetraacetic acid (Co-EDTA) and ytterbium (Yb) labeled neutral detergent fiber (NDF) before an 84-h total fecal collection to determine digesta retention time. Dry matter digestibility was greatest for ALF (62.1%) and least for CB 6 (36.0%) and CB 8 diets (36.8%, SEM = 2.1; p < 0.05). Mean retention time was longer (p < 0.05) for Coastal bermudagrass (particulate 31.3 h, liquid 25.3 h) compared with ORCH and ALF (28.0 h, SEM = 0.88 h; 20.7 h, SEM = 0.70 h). Further evaluation of digesta passage kinetics through mathematical modeling indicated ALF had distinct parameters compared to the other diets. Differences in digestive variables between forage types are likely a consequence of fiber physiochemical properties, warranting further investigation on forage fiber and digestive health.

Survival Probability Dynamics of Scaled Brownian Motion: Effect of Nonstationary Property

Scaled Brownian motion (SBM) is a popular model of nonstationary anomalous diffusion process. We here extend the SBM model to investigate the survival probability of stationary anomalous diffusion process. By making comparison between the SBM model and the stationary SBM model, we investigate the effect of stationarity on the first passage kinetics.

Increasing intake of dietary soluble nutrients affects digesta passage rate in the stomach of growing pigs.

The passage rate of solids and liquids through the gastrointestinal tract differs. Increased dietary nutrient solubility causes nutrients to shift from the solid to the liquid digesta fraction and potentially affect digesta passage kinetics. We quantified: (1) the effect of three levels of dietary nutrient solubility (8, 19 and 31 % of soluble protein and sucrose in the diet) at high feed intake level (S) and (2) the effect of low v. high feed intake level (F), on digesta passage kinetics in forty male growing pigs. The mean retention time (MRT) of solids and liquids in the stomach and small intestine was assessed using TiO2 and Cr-EDTA, respectively. In addition, physicochemical properties of digesta were evaluated. Overall, solids were retained longer than liquids in the stomach (2·0 h, P<0·0001) and stomach+small intestine (1·6 h, P<0·001). When S increased, MRT in stomach decreased by 1·3 h for solids (P=0·01) and 0·7 h for liquids (P=0·002) but only at the highest level of S. When F increased using low-soluble nutrients, MRT in stomach increased by 0·8 h for solids (P=0·041) and 0·7 h for liquids (P=0·0001). Dietary treatments did not affect water-binding capacity and viscosity of digesta. In the stomach of growing pigs, dietary nutrient solubility affects digesta MRT in a non-linear manner, while feed intake level increases digesta MRT depending on dietary nutrient solubility. Results can be used to improve predictions on the kinetics of nutrient passage and thereby of nutrient digestion and absorption in the gastrointestinal tract.

Magnesium absorption as influenced by the rumen passage kinetics in lactating dairy cows fed modified levels of fibre and protein

The potassium sensitive magnesium absorption through the rumen wall may be influenced by additional dietary properties, such as diet type, forage type or forage to concentrate ratio. These properties are likely associated to rumen passage kinetics modified by dietary fibre content. The study aimed to assess the effects of rumen passage kinetics on apparent Mg absorption and retention in lactating dairy cows fed modified levels of fibre. Six lactating Red-Holstein and Holstein cows, including four fitted with ruminal cannulas were randomly assigned to a 3 × 3 cross-over design. The experimental diets consisted of early harvested low NDF (341 g NDF/kg DM) and late harvested high NDF (572 g NDF/kg DM) grass silage (80% DM) and of concentrates (20% of DM). As the low-fibre diet was excessive in protein, a third high-fibre diet was formulated to be balanced in digestible protein with the low-fibre diet to avoid any eventual confounding effects of NDF and protein excess. All diets were formulated to contain iso-Ca, -P, -Mg, -K and -Na. Passage kinetics of solid and liquid phase of rumen digesta were evaluated using ruminal marker disappearance profiles. Cows fed the low-fibre diet had compared to the other diets, an up to 40% lower solid and 26% lower liquid phase volume of rumen digesta and a 10% numerically higher fractional rumen liquid passage rate. Rumen pH lost 0.6 units and Mg concentration in the rumen liquid phase tripled when cows were fed the low-fibre diet. Faecal Mg excretion was up to 14% higher in cows fed the low-fibre diet and Mg absorbability was 12% compared to up to 19% in other diets. Urinary Mg excretion in cows fed the low-fibre diet was half of the ones in the other treatments, but Mg retention was not affected. Dietary protein excess neither affected rumen passage kinetics nor Mg absorption and retention. Absorption of Mg was correlated with rumen liquid volume which both decreased with decreasing daily NDF intake (NDFi, 11.8 ± 2.4 l/kg NDFi). Consequently, daily Mg absorption decreased by 1.32 ± 0.28 g/kg decreasing NDFi. To conclude, in addition to the known antagonistic effect of dietary K, the present data indicate that Mg absorption was dependent from NDFi which modified rumen liquid volume, but was independent of dietary protein excess likely associated to low NDF herbages.

Technical note: Infusion, sampling, and vacuum-assisted collection devices for use in ruminally cannulated calves

Calves can be ruminally cannulated at young ages, but equipment size limitations preclude use of an infusion and sampling device in these small animals. Likewise, a procedure to easily evacuate rumen contents in young calves has not been described. Overcoming these technical complications related to assessment of ruminal passage kinetics, nutrient digestion, and volatile fatty acid absorption would aid in future studies advancing our knowledge of dairy calf nutrition. The first objective was to design and fabricate 2 devices (one device for infusion and sampling, and another for vacuum-assisted collection) suitable for use in young ruminally cannulated dairy calves. The second objective was to test the utility of these tools when performing procedures commonly used in ruminant nutrition research. A single weaned 62-d-old ruminally cannulated calf was used to evaluate the ability to infuse a solution of LiCoEDTA and sample rumen contents through the cannula cap over a period of 2 h to assess the rumen liquid passage rate (procedure 1). The device was capable of infusing the LiCoEDTA and sampling the rumen fluid, as evidenced by the presence of elevated Co concentrations in the sampled rumen fluid. Using the fluid samples obtained, liquid passage rate within the calf was estimated to be 40.2% of ruminal fluid/h. The second procedure tested the vacuum-assisted collection device and consisted of evacuating and weighing the rumen contents, which is considered a key preparatory step in washed reticulorumen technique experiments that aim to measure nutrient absorption. In agreement with existing literature, evacuated rumen contents represented approximately 4% of the calf's body weight. In conclusion, custom-built devices for infusion, sampling, and vacuum-assisted collection were efficacious when tested in a 62-d-old ruminally cannulated calf fed a diet of 100% texturized starter (18% crude protein, as-fed). Fellow scientists may employ and further modify these techniques to suit their needs when assessing passage kinetics, nutrient digestion, and volatile fatty acid absorption in calves.

Polyethylene glycol as an indigestible marker to estimate fecal output in dairy cows

The objective of this study was to evaluate the accuracy of fecal output measurements using polyethylene glycol (PEG) as an external marker determined by near-infrared reflectance spectroscopy. In addition, the accuracy of dry matter intake predictions based on fecal output and digestibility estimated using an internal marker [indigestible neutral detergent fiber (iNDF)] was assessed. The experiment was conducted using 6 lactating dairy cows fed 2 different diets. Polyethylene glycol was administered twice daily into the rumen and the diurnal pattern of fecal concentrations and recovery in feces were determined. To evaluate the effects of alternative marker administration and sampling schemes on fecal output estimates, the passage kinetics of PEG in the digestive tract of dairy cows was determined and used for simulation models. The results indicate that PEG was completely recovered in feces and, thus, fecal output was accurately estimated using PEG. Good agreement between measured and predicted dry matter intake (standard error of prediction = 0.86 kg/d, R2 = 0.81) indicates good potential to determine feed intake using PEG in combination with iNDF. The precision of cow-specific digestibility estimates based on iNDF was unsatisfactory, but for a group of cows iNDF provided an accurate estimate of dry matter digestibility. The current study indicated that, to overcome inherent day-to-day variation in feed intake and fecal output, the minimum of 4 fecal spot samples should be collected over 4 d. Preferably, these samples should be distributed evenly over the 12-h marker administration interval to compensate for the circadian variation in fecal PEG concentrations.

Effects of feeding systems on rumen environment, degradability and passage kinetics in Ankole × Friesian crossbred steers

Natural pastures constitute a large proportion of the feed resource base for meat and milk production in Sub-Saharan Africa. However, there is increasing use of agro-industrial by-products, especially those that are cereal-based as supplementary feedstuff to grazing animals and in diets under semi-intensive and intensive production systems. This study evaluated the influence of feeding systems on rumen environment, degradability and passage kinetics. Six Ankole x Friesian F1 crossbred steers weighing 339 ± 29 kg (about two years of age), each fitted with permanent rumen cannula were used in a replicated 3 × 3 Latin square design (ns = 2). Two steers were allocated per period to one of three feeding systems i.e. (1) sole grazing (control), (2) control plus concentrate supplement (composition g/kg DM: 375 maize bran, 559 brewer's spent grain, 62.5 molasses and 3.75 NaCl), and (3) feedlot systems where steers were fed total mixed ration (TMR) comprising g/kg DM: 200 maize stover, 300 maize bran, 447 brewers’ spent grain, 50 molasses and 3 NaCl. Data was collected on rumen pH, ammonia-nitrogen (NH3-N), volatile fatty acids (VFA) and degradability of dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF). Rumen pH was lowest (P < 0.001) at feedlot (5.3) but highest (P < 0.001) under sole grazing (6.2). Rumen NH3-N ranged between 62.8 and 120 mg/l and was higher (P < 0.001) in sole grazing than in grazing but supplemented steers and those at the feedlot. Total VFA concentration for sole grazing steers (124 mmol/Mol) was higher (P < 0.05) than values observed under feedlot (102 mmol/Mol) while grazing but supplemented steers showed an intermediate value (108 mmol/Mol), not differing significantly from the two other systems. Molar proportion of acetate was higher (P < 0.001) in grazing steers compared to values for either grazing but supplemented or those under feedlot while the reverse was true for propionate. The degradation characteristics of DM, CP and NDF were generally higher in sole grazing steers. Although, in most cases, the influence of feeding system on degradability was dependent on the type of feedstuff, feeding systems did not influence total mean retention time. The high extent of DM, CP and fiber degradation in grazing steers compared to supplemented and feedlot steers demonstrates that forage diversity under grazing positively influences degradability. However, attention to the nature and fermentation characteristics of proteins and carbohydrate sources and how they modify rumen environment in different production systems is needed to improve utilization of supplements and TMR.

Preparation of synthetic alkane waxes and investigations on their suitability for application as dietary markers in farm animals

Synthetic alkanes can be applied as external markers to estimate faecal output, digestibility and passage kinetics and are furthermore easy to combine with plant alkanes for the estimation of feed intake. Successful application requires an accurate and uniform labelling of boluses or feedstuffs, which is in turn supported through simplified handling of the markers during preparation. In this study, it was tested whether melting of synthetic alkanes to wax is able to enhance the accuracy and uniformity of subsequent bolus labelling and further simplifies it. The preparation of alkane waxes was performed on model scale using a portion in a ratio of approximately 1:300 to a dosage, which is recommended for administration in large livestock 2 times a day. Additionally, the temperature sensitivity of a range of synthetic alkanes was studied to clarify so far non-explained losses of alkanes, which were observed frequently during the labelling of boluses and feedstuffs or the processing of samples for analysis. Using n-octacosane (C28), n-dotriacontane (C32) and n-hexatriacontane (C36) synthetic alkanes, three single-component waxes (of C28, C32 and C36, respectively), three binary waxes (C28:C32, C28:C36 and C32:C36) and one tertiary mixed wax (C28:C32:C36) were produced with 30 repetitions each. To assess the impact of melting and re-crystallization, the quantity of individual alkanes was determined by gas chromatographic analysis (GCA) in untreated crystals, crystalline mixtures (GCA1) and the finished model waxes (GCA2). Additionally, sub-samples of the waxes were heated for 30min at 100°C or freeze-dried for 48h, respectively, to simulate baking of boluses or freeze-drying as an alternative method for preparation (GCA3). The temperature sensitivity of n-tetracosane (C24) to n-octatriacontane (C38) even-chain alkanes was studied by thermogravimetric analysis (TGA) with consistently increasing temperature (20 to maximal 600°C at 10K/min, TGA1) and under isothermal conditions (180°C for 20min, TGA2), respectively. Depending on chain length and thus molecular weight of alkanes, weight reduction by emergence of soot during heating-up started between 176°C (C24) and 227°C (C38) and further increased rapidly. Throughout isothermal treatment, weight loss from alkanes was lowest with highest chain length (0.0% for C38) and vice versa (23.8% for C24). The originally weighed and via GCA measured quantities of crystalline alkanes did not differ (P>0.05), except for single C36, where the measured quantities were always higher than the weighed ones (P=0.019). The weighed and measured quantities of individual alkanes in single-component and of total alkanes in multi-component waxes were similar with a maximal relative difference of 6.6±5.5%, given as the mean ± standard deviation among the repetitions of a sample variant. The relative difference between weighed and measured quantities of individual alkanes in multi-component waxes was maximal 47.4±25.7% and was highly variable. Unexpectedly, the relative difference between weighed and measured quantities was low for C28 (5.9±5.8%) and C32 (5.7±4.3%) in their combined binary waxes. The additional treatment (baking or freeze-drying) did not alter the recovery of alkanes from the model waxes. Synthetic alkanes are thermolabile why exposure to high temperature during preparation of boluses or labelling of feedstuffs needs to be assessed critically. Reasons for that might be complex disorders of the conformation of alkane molecules particularly during the melting of alkane mixtures and the apparently incomplete separation following re-crystallization from the melt. This may lead to displacements within waxes, which cannot be foreseen or quantified, and thus to the loss of their suitability as dietary markers. Alkane recovery from binary waxes of C28 and C32 was unbiased on model scale and whether this can be confirmed on original scale needs to be validated further. For practical use, alkane waxes might nevertheless be beneficial because the handling is easier than that of alkane crystals.

Effects of solid feed level and roughage-to-concentrate ratio on ruminal drinking and passage kinetics of milk replacer, concentrates, and roughage in veal calves

Effects of solid feed (SF) level and roughage-to-concentrate (R:C) ratio on ruminal drinking and passage kinetics of milk replacer, concentrate, and roughage were studied in veal calves. In total, 80 male Holstein-Friesian calves (45±0.2kg of body weight) were divided over 16 pens (5 calves per pen). Pens were randomly assigned to either a low (LSF) or a high (HSF) SF level and to 1 of 2 R:C ratios: 20:80 or 50:50 on a dry matter (DM) basis. Roughage was composed of 50% corn silage and 50% chopped wheat straw on a DM basis. At 27 wk of age, measurements were conducted in 32 calves. During the measurement period, SF intake was 1.2kg of DM/d for LSF and 3.0kg of DM/d for HSF, and milk replacer intake averaged 2.3kg of DM/d for LSF and 1.3kg of DM/d for HSF. To estimate passage kinetics of milk replacer, concentrate, and straw, indigestible markers (CoEDTA, hexatriacontane C36, Cr-neutral detergent fiber) were supplied with the feed as a single dose 4, 24, and 48h before assessment of their quantitative recovery in the rumen, abomasum, small intestine, and large intestine. Rumen Co recovery averaged 20% of the last milk replacer meal. Recoveries of Co remained largely unaffected by SF level and R:C ratio. The R:C ratio did not affect rumen recovery of C36 or Cr. Rumen fractional passage rate of concentrate was estimated from recovery of C36 in the rumen and increased from 3.3%/h for LSF to 4.9%/h for HSF. Rumen fractional passage rate of straw was estimated from Cr recovery in the rumen and increased from 1.3%/h for LSF to 1.7%/h for HSF. An increase in SF level was accompanied by an increase in fresh and dry rumen contents. In HSF calves, pH decreased and VFA concentrations increased with increasing concentrate proportion, indicating increased fermentation. The ratio between Cr and C36 was similar in the small and large intestine, indicating that passage of concentrate and straw is mainly determined by rumen and abomasum emptying. In conclusion, increasing SF level introduces large variation in passage kinetics of dietary components, predominantly in the rumen compartment. The SF level, rather than the R:C ratio, influences rumen recovery of concentrate and roughage. Our data provide insight in passage kinetics of milk (Co representing the milk replacer) and SF (Cr and C36 representing roughage and concentrate, respectively) and may contribute to the development of feed evaluation models for calves fed milk and SF.

Nordic dairy cow model Karoline in predicting methane emissions: 1. Model description and sensitivity analysis

Decreasing methane (CH4) emissions is necessary both environmentally, as CH4 has a strong greenhouse gas effect and nutritionally as CH4 represents a loss of feed energy. Karoline is a whole dairy cow mechanistic, dynamic model predicting nutrient supply and milk production. The objectives of this study were to revise the digestion and CH4 emissions modules of the Karoline model. In addition, a sensitivity analysis was conducted to evaluate the importance of the accuracy of input data required in predicting CH4 emissions. Modifications were made in the equations predicting digesta passage kinetics, microbial cell synthesis, digestion in the hind-gut, and utilization of hydrogen. The Karoline model predicted similar decreases in both organic digestibility (OMD) and neutral detergent fibre digestibility (NDFD) and improvements in the efficiency of microbial nitrogen synthesis with increasing dry matter intake (DMI) as reported in the literature. The proportion of ruminal digestion of total NDFD (0.95) and fecal metabolic and endogenous output (98g/kg DMI) also agree with the literature data. Predicted total CH4 emissions increased with a diminishing rate by increased DMI. Predicted CH4 emissions as a proportion of GE intake decreased linearly with increased DMI. The relationships between feeding level and CH4 emissions (a decrease of 7.8kJ/MJ gross energy per multiple of maintenance) were in good agreement with experimental data. The sensitivity analysis suggested that feed variables related to digestion kinetics of NDF [indigestible NDF (iNDF) and digestion rate of potentially digestible NDF] have a strong influence on predicted CH4 emissions; for example, predicted CH4 emissions decreased with increasing iNDF concentration. Digestion rates of starch and insoluble protein had smaller effects on predicted CH4 emissions than NDF digestion rates. Fat had a strong negative influence on predicted CH4 emissions (0.27kJ/MJ gross energy per 1g fat/kg DM). The sensitivity analysis suggested that accurate values of digestion kinetic variables are required for satisfactory predictions of CH4 emissions with mechanistic models. Based on reliable predictions of digestibility, microbial protein synthesis and CH4 emissions, it can be concluded that the revised Karoline model is a promising tool for predicting CH4 emissions and understanding the underlying mechanisms.

Excretion patterns of solute and different-sized particle passage markers in foregut-fermenting proboscis monkey (Nasalis larvatus) do not indicate an adaptation for rumination

Behavioral observations and small fecal particles compared to other primates indicate that free-ranging proboscis monkeys (Nasalis larvatus) have a strategy of facultative merycism (rumination). In functional ruminants (ruminant and camelids), rumination is facilitated by a particle sorting mechanism in the forestomach that selectively retains larger particles and subjects them to repeated mastication. Using a set of a solute and three particle markers of different sizes (<2, 5 and 8mm), we displayed digesta passage kinetics and measured mean retention times (MRTs) in four captive proboscis monkeys (6–18kg) and compared the marker excretion patterns to those in domestic cattle. In addition, we evaluated various methods of calculating and displaying passage characteristics. The mean±SD dry matter intake was 98±22gkg−0.75d−1, 68±7% of which was browse. Accounting for sampling intervals in MRT calculation yielded results that were not affected by the sampling frequency. Displaying marker excretion patterns using fecal marker concentrations (rather than amounts) facilitated comparisons with reactor theory outputs and indicated that both proboscis and cattle digestive tracts represent a series of very few tank reactors. However, the separation of the solute and particle marker and the different-sized particle markers, evident in cattle, did not occur in proboscis monkeys, in which all markers moved together, at MRTs of approximately 40h. The results indicate that the digestive physiology of proboscis monkeys does not show typical characteristics of ruminants, which may explain why merycism is only a facultative strategy in this species.