Total Tract Mean Retention Time Research Articles

Effect of induced saliva flow on fluid retention time, ruminal microbial yield and methane emission in cattle.

Both in vitro and animal studies indicated that a higher dilution rate is related to a more efficient microbial synthesis and a lower methane (CH4 ) yield. The latter could be a consequence of the former, as an increase in microbial cell synthesis offers an alternative hydrogen sink competing with methanogenesis. To test this assumption in live animals, we applied a saliva stimulant, pilocarpine, to modify liquid flow rate in cattle. Four non-lactating cows (750 ± 71 kg) were fed forage only (restricted to constant intake) in a 4 × 4 Latin square design with oral doses of 0, 1, 2.5 and 5mg pilocarpine/kg body weight and day. We quantified feed and water intake, ruminal and total tract mean retention time (MRT) of solute and particle markers, ruminal microbial yield (via urinary purine bases or metabolic faecal nitrogen), CH4 emission, digestibility, chewing behaviour, reticular motility and rumen fluid parameters. The effect of induced saliva flow was evident by visibly increased salivation and water intake. Increasing the pilocarpine dosages resulted in a linearly decreased MRT of fluid and small particles (p < 0.001 and p< 0.05, respectively) and methane yield as related to digested DM (p < 0.05), the latter at a magnitude of 5%. No effect of treatment was found on ruminal microbial yield estimated via purine derivates. Metabolic faecal N as an indicator of microbial growth linearly correlated with pilocarpine dosages (p < 0.05). No significant relationship was found between pilocarpine dosages and large particle MRT, nutrient digestibility, ruminal pH and short-chain fatty acids. In conclusion, different from some in vitro studies, there was little indication of a reciprocal effect of CH4 and microbial biomass production in cows fed a forage-only diet.

Modeling digesta retention in horses fed high or low neutral detergent fiber concentration forages

One factor influencing the extent of feed degradation is the length of time feed resides at the site of digestion. Traditionally, mean retention time (MRT) is measured for the entire equine gastrointestinal tract (GIT), but retention time in specific organs may be more relevant to understanding digestion. Multi-compartment models theoretically partition the GIT to potentially represent MRT in individual segments. The objective of this study was to apply a multi-compartment model to digesta passage in horses fed forage-based diets. We hypothesized forage neutral detergent fiber concentration would alter total tract MRT, transit time (TT), and compartment retention time. Six geldings (4 ± 1.5 y, 545.0 ± 64.5 kg, mean ± SD) were randomly assigned a diet of timothy cubes (Hi NDF, n = 3) or alfalfa cubes (Lo NDF, n = 3) fed at 1.53% BW and concentrate at 0.22% BW (DM basis). After a 15-d dietary adaptation, geldings were orally dosed with Co-EDTA and Yb-labeled NDF residue to determine liquid and particulate retention time. A total fecal collection was conducted for 120 h after marker dosing. Samples were analyzed for Co and Yb concentrations by inductively coupled plasma spectrometry. Gamma distributed age-dependent two compartment models were fit to marker excretion curves for each gelding (MATLAB, vR2014a). Diet effects were analyzed by ANOVA (SAS, v9.3). There was no effect of diet on total tract MRT (liquid 21.78 ± 0.79 h, particulate 25.80 ± 0.79 h, mean ± SEM). However, liquid TT was longer (P = 0.041) in the Hi NDF diet (7.25 ± 0.91 h) than the Lo NDF diet (3.86 ± 0.91 h), and liquid age-dependent compartment retention time was shorter (P = 0.019) in the Hi NDF diet (8.40 ± 0.84 h) compared with Lo NDF diet (11.72 ± 0.84 h). Particulate TT was longer (P = 0.029) in the Hi NDF diet (8.24 ± 0.96 h) than the Lo NDF diet (4.54 ± 0.96 h). Although there was a difference in DM digestibility (Hi NDF: 50.1 ± 2.31%; Lo NDF: 60.0 ± 2.31%; P = 0.002), covariate analysis did not show a significant relationship between MRT or compartment parameters to diet digestibility. Additional research should pursue methods to ascribe physiological meaning to mathematically determined compartments. Nonetheless, the current data indicate using a multi-compartment model can identify differences in some digesta rate parameters between high and low fiber diets that were not apparent using total tract MRT alone.

A Pilot Study Exploring the Relationship Between Digesta Retention Time in the Equine Gastrointestinal Tract and Compartment Models

Digesta retention time within specific segments of the equine gastrointestinal tract (GIT) may be more relevant to scientific inquiries than total tract mean retention time (TTMRT); however, measuring retention time in individual segments requires access to the digestive tract. The objective of this study was to compare prececal, cecal, and colonic mean retention time (MRT) with model-derived compartment MRT. A cecally fistulated gelding was fed indigestible particulate and liquid markers to determine TTMRT and dosed with different pairs of particulate and liquid markers into the cecum (hindgut MRT) and into the right ventral colon through the cecocolic orifice (colon MRT). Fecal marker concentrations were fit to stochastic and mechanistic models using nonlinear least squares methods (MATLAB). Total tract MRT and MRT for each GIT segment were compared with model-derived compartment MRT using paired t-test to determine differences and two one-sided tests to determine equivalence. All models resulted in parameter estimates and an acceptable fit to fecal marker excretion curves, but some parameter estimates did not differ from zero (95% CI included 0). Model-derived TTMRT were equivalent (P < .05) to arithmetically calculated MRT. Most GIT segment MRT differed (P < .05) from model-derived compartment MRT. Differences ranged from −26.1 hours to 25.8 hours. In these exploratory data, model derived compartment retention times failed to pair with MRT in different GIT segments. Significant methodological and analytical challenges remain to describe retention time in individual segments of the equine GIT.

The impact of nonsteroidal anti-inflammatory drugs on the equine gastric microbiome

Digesta retention time within specific segments of the equine gastrointestinal tract (GIT) may be more relevant to scientific inquiries than total tract mean retention time (TTMRT); however, measuring retention time in individual segments requires access to the digestive tract. The objective of this study was to compare prececal, cecal, and colonic mean retention time (MRT) with model-derived compartment MRT. A cecally fistulated gelding was fed indigestible particulate and liquid markers to determine TTMRT and dosed with different pairs of particulate and liquid markers into the cecum (hindgut MRT) and into the right ventral colon through the cecocolic orifice (colon MRT). Fecal marker concentrations were fit to stochastic and mechanistic models using nonlinear least squares methods (MATLAB). Total tract MRT and MRT for each GIT segment were compared with model-derived compartment MRT using paired t-test to determine differences and two one-sided tests to determine equivalence. All models resulted in parameter estimates and an acceptable fit to fecal marker excretion curves, but some parameter estimates did not differ from zero (95% CI included 0). Model-derived TTMRT were equivalent (P < .05) to arithmetically calculated MRT. Most GIT segment MRT differed (P < .05) from model-derived compartment MRT. Differences ranged from −26.1 hours to 25.8 hours. In these exploratory data, model derived compartment retention times failed to pair with MRT in different GIT segments. Significant methodological and analytical challenges remain to describe retention time in individual segments of the equine GIT.

Effects of quebracho tannin extract and activated charcoal on nutrient digestibility, digesta passage and faeces composition in goats

Irrigation agriculture of hot climates suffers from rapid soil organic carbon (C) turnover, high nitrogen (N) leaching and gaseous losses. In this context, we explored the possibility of supplementing ruminants with activated charcoal (AC) and condensed tannins (CT) to increase faecal concentration of long-lived C and slowly decomposable N. For this purpose, we fed AC and quebracho tannin extract (QTE, source of CT) to goats and determined nutrient digestibility, digesta passage and composition of faeces. The feeding trial comprised three periods, with 24 male goats assigned to five treatments and a control. On dry matter (DM) basis, the basal diet (control) consisted of 50% hay, 46.5% crushed maize and 3.5% soya bean meal. Treatment diets contained (on DM basis) 2% and 4% QTE (QTE2, QTE4), 1.5% and 3.0% AC (AC1.5, AC3.0) and a mixture of 2% QTE plus 1.5% AC (QTEAC). Samples of feed, refusals and faeces were analysed for chemical constituents; digesta passage was computed with a one-compartment Gamma-2 model from pulse-dose application of ytterbium-mordanted fibre and quantitative collection of faeces during 7days. Compared to the control, organic matter and N digestibility were reduced with QTE2 and QTE4 (p≤0.001), that of neutral and acid detergent fibre (NDFom, ADFom) decreased with QTE4, QTEAC and both AC treatments (p≤0.001). Ruminal particle passage ranged from 0.051h-1 (QTEAC) to 0.056h-1 (control; p>0.05). Apart from the correlation between total tract mean retention time and faecal C/N ratio (r=-0.35), passage parameters did not affect faeces quality. While faecal N concentration was not altered by both additives, AC enhanced faecal NDFom, ADFom and C concentrations (p≤0.001). Whereas feeding up to 3% AC might slow down the decomposition of manure in the field without negatively affecting the digestive physiology of goats, including QTE seems not advantageous from a physiological and nutrient recycling perspective.

Effect of grass hay intake on fiber digestion and digesta retention time in the hindgut of horses

Eight Thoroughbred horses were used to examine the effects of grass hay intake on the fiber digestion and the retention time of digesta in the total gastrointestinal tract and the hindgut segments. The horses were randomly assigned to 2 groups and offered 2.0 (high intake [HI]) or 1.3 kg DM/(100 kg BW • d; low intake [LI]) of timothy hay in equal amounts every 3 h for 17 d. The digestibility and total tract mean retention time of digesta (tMRT) in the total gastrointestinal tract were measured from d 11 to d 15. To measure the mean retention time of digesta in each hindgut segment (sMRT), the horses were euthanized on d 17, after being fed a series of hay markers that were labeled with different rare earth elements. The digesta were collected from the ileum, cecum, right ventral colon (RVC), left ventral colon (LVC), left dorsal colon, right dorsal colon (RDC), and small colon (SC) to measure fiber digestibility, sMRT, VFA concentration, and fibrolytic activities. The digestibility of NDF and ADF in the total gastrointestinal tract was lower (P < 0.01) for HI than for LI. The cumulative disappearance of NDF and ADF from the ileum to the LVC attained 90% of total tract digestion regardless of hay intake. Values did not differ according to treatments in the ileum and the cecum but were lower (P < 0.01) for HI than for LI in the postcecal segments. This was caused by the smaller increase in the cumulative NDF and ADF disappearance from the cecum to the RVC for HI than for LI. The solid phase tMRT was shorter (P = 0.04) for HI than for LI. Although sMRT in the RDC and SC were shorter (P = 0.04 and P < 0.01, respectively) for HI than for LI, no differences were observed in the other hindgut segments. There was no difference between treatments in the total VFA concentration, VFA proportions, or the specific activity of carboxymethyl cellulase and xylanase in each hindgut segment. The fibrolytic activity for the cecum and RVC were greatest and decreased beyond the LVC. A clear relation between mean retention time and fiber digestion was observed in the total gastrointestinal tract, but the segments where a difference in sMRT was detected because of the intake were not the same as those with the fiber digestibility depression. Although the reduction in total tract fiber digestibility with increased feed intake was clearly shown to occur between the cecum and RVC, which were the main segments for fiber digestion, it could be explained neither by the sMRT nor by the fibrolytic activity in these segments.

Impact of fibre intake and fibre source on digestibility, gut development, retention time and growth performance of indigenous and exotic pigs

The impact of fibre level and fibre source on digestibility, gastrointestinal tract (GIT) development, total tract mean retention time (MRT) and growth performance was studied in indigenous Mong Cai (MC) and exotic Landrace × Yorkshire (LY) pigs. The diets were based on maize, rice bran, soyabean meal, fish meal and soyabean oil, and cassava residue (CR) or brewer's grain (BG) as fibrous ingredient sources in the high-fibre diets (HF) and were fed ad libitum. A low-fibre diet (LF), containing around 200 g NDF/kg dry matter (DM), was formulated without CR and BG as feed ingredients. The HF diets (HF-CR and HF-BG) were formulated to contain around 270 g NDF/kg DM. The experiment was arranged as a 2 × 3 factorial completely randomized design with six replications, and lasted 27 days. Increased dietary fibre level resulted in a reduction (P < 0.05) in average daily gain, digestibility of organic matter (OM), CP and gross energy (GE) at the ileum and in the total tract, and in MRT, and an increase (P < 0.05) in the feed conversion ratio and in the weight of the GIT (except for small intestine and caecum). The coefficients of total tract digestibility of fibre fractions were higher in HF diets than in the LF diet, with highest values for diet HF-CR, which had a high proportion of soluble non-starch polysaccharides. MC pigs had longer MRT of digesta than LY pigs (P < 0.05), resulting in higher digestibility at the ileum and in the total tract. Across diets and breeds, the total tract apparent digestibility of OM, CP and GE was positively related (R2 = 0.80 to 0.84) to the MRT of solids, whereas the MRT was negatively related to the DM intake (R2 = 0.60).

No distinct difference in the excretion of large particles of varying size in a wild ruminant, the banteng (Bos javanicus)

The forestomach of ruminants and camelids does not only allow a differential excretion of fluids and small particles but also a differential excretion of small and large particles. The question whether larger particles of different size classes are also retained for different time periods, or whether simply a particle-size threshold exists above which all particles of a size higher than this threshold are retained in an undifferentiated manner, has not been addressed so far. We determined the mean retention time (MRT) of different-sized large particles (10 and 20 mm) in three banteng (Bos javanicus) on two forage only diets, grass and grass hay. We used cerium-mordanted fibre (10 mm) and lanthanum-mordanted fibre (20 mm) as particle markers, mixed in the food. Average total tract MRT for large and very large particles at the grass diet was 58 and 56 h and at the grass hay diet 66 and 64 h, respectively. Very large particles moved slightly faster than large particles through the gut of the banteng. Three interpretations are possible: Very large particles are resubmitted to rumination sooner than large particles; ingestive mastication of the particle markers could have reduced the difference in the size of the particle markers; alternatively, particle retention may be governed by a threshold, above which all particles of a size higher than this threshold are retained in an undifferentiated manner. In order to test these possibilities, experiments with fistulated animals would have to be performed.

Excretion patterns of fluid and different sized particle passage markers in banteng ( Bos javanicus) and pygmy hippopotamus ( Hexaprotodon liberiensis): Two functionally different foregut fermenters

Processing of ingesta particles plays a crucial role in the digestive physiology of herbivores. In the ruminant forestomach different sized particles are stratified into a small and a large particle fraction and only the latter is regurgitated and remasticated to smaller, easier-to-digest particles. In contrast, it has been suggested that in non-ruminating foregut fermenters, such as hippopotamuses, larger particles should be selectively excreted since they tend to be digested at a slower rate and hence can be considered intake-limiting bulk. In our study we determined the mean retention time (MRT) of fluids and different sized particles (2 mm and 10 mm) in six pygmy hippos ( Hexaprotodon liberiensis) and six banteng ( Bos javanicus) on a diet of fresh grass at two intake levels. We used cobalt ethylendiamintetraacetate (Co-EDTA) as fluid and chromium (Cr)-mordanted fibre (2 mm) and cerium (Ce)-mordanted fibre (10 mm) as particle markers, mixed in the food. Average total tract MRT for fluid, small and large particles at the high intake level was 32, 76 and 73 h in pygmy hippos and 25, 56 and 60 h in banteng, and at the low intake level 39, 109, and 105 h in pygmy hippos and 22, 51 and 58 h in banteng, respectively. In accordance with the prediction, large particles moved faster than, or as fast as the small particles, through the gut of pygmy hippos. In contrast, large particles were excreted slower than the small particles in the ruminant of this study, the banteng. Pygmy hippos had longer retention times than the banteng, which probably compensate for the less efficient particle size reduction. Although the results were not as distinct as expected, most likely due to the fact that ingestive mastication of the larger particle marker could not be prevented, they confirm our hypothesis of a functional difference in selective particle retention between ruminating and non-ruminating foregut fermenters.

Gastrointestinal passage of Sahelian roughages in cattle, sheep and goats, and implications for livestock-mediated nutrient transfers

Green and dry pasture vegetation and millet crop residues are the main feed for domesticated ruminants across the West African Sahelian zone. Studying their gastrointestinal passage is important for modelling livestock-mediated nutrient flows in these agro-pastoral systems. Intake, passage, digestion and excretion were studied in 16 cattle, 16 sheep and 16 goats offered these feeds at levels corresponding to 0.8 and 1.3 times voluntary feed intake. Parameters of particle passage were derived from faecal excretion of a pulse-dose of short (1–2 mm) and long (>2 mm) particles labelled with Ytterbium, using age-dependent Gamma-2 single-compartment models. Across the three species, mean retention time of particles in the mixing compartment (CMRT) varied between 39–50 and 54–66 h in green and dry pasture vegetation and between 66 and 88 h in millet leaves, and was always longer in cattle than in small ruminants (P<0.05). Particle passage through the mixing compartment ( λ), particle half life ( T 50) and total tract mean retention time (TMRT) were correlated to the dry matter digestibility and to the contents of nitrogen and neutral detergent fibre of the ingested diet, while particle size had no and feed intake only a weak influence on these parameters. The results suggest that seasonal and species-specific differences in gastrointestinal passage of feed particles should be taken into account when addressing the temporal aspects of livestock-mediated matter and nutrient flows across the agro-pastoral landscapes of the Sahel.

Influence of passage model and caecal cannulation on estimated passage kinetics of roughage and concentrate in the gastrointestinal tract of horses

The objectives of this study were to evaluate the use of non-linear passage models to estimate total tract retention time and hindgut fractional passage rates of hay and concentrate, and to investigate the effect of caecal cannulation on passage parameters in horses. Animals were four geldings of Norwegian Cold-blooded Trotter fed a hay and concentrate diet at a dry matter intake of 1.7% of body weight. Marker studies were conducted one month before and three and 15 months after caecal cannulation using Cr-mordanted hay and Yb-labelled concentrate as markers. Faecal marker excretion curves were fitted either to one-compartment models with gamma time dependency (Gn) or to two-compartment models (GnG1), with gamma time dependency in the first compartment (Gn) and time independency in the second one (G1). Lowest error mean square was observed for the G4 and G4G1 models. Caecal cannulation increased total tract mean retention time (TMRT). No differences were observed between hay and concentrate in TMRT or fractional passage rates. It is concluded that using time dependent passage models will improve our understanding of passage kinetics in horses and that there is only minor differences between hay and concentrate in hindgut retention time.

Algebraic methods to determine total tract mean retention time of digesta in ponies given ad libitum access to pelleted diets containing different levels of unmolassed sugar beet pulp

Digesta passage rate may have influenced previously reported work on the intakes, apparent digestibilities and nutritive values of complete pelleted diets containing unmolassed sugar beet pulp (USBP) at levels ranging from 0-800 g/kg dry matter (DM) when offered to ponies (Hyslop, 2002). This study’s objective was to compare total tract mean retention time (TMRT) of digesta using two algebraic calculation methods in the same ponies.

Composition and digestive tract retention time of ruminal particles with functional specific gravity greater or less than 1.02.

The objective of this study was to determine composition, particle size distribution, and in vivo kinetics of ruminal particles having functional specific gravity (FSG) greater or less than FSG of particles found in the omasum and reticulum of lactating dairy cows. Particles from the reticulum and the omasal had FSG of 1.03 and 1.02, respectively. Particles from ruminal contents with FSG higher (HP) or lower (LP) than 1.02 were isolated and labeled with Er or Dy, respectively. Four ruminally cannulated, lactating Ayrshire dairy cows were fed all-grass silage (AS) or 54% grass silage:46% concentrate (SC) diets in a cross-over design trial and used to study chemical composition and ruminal and total tract kinetics of HP and LP. Labeled particles were pulse dosed into the rumen of the cows and disappearance of the markers from ruminal HP and LP pools and excretion in feces was monitored for 72 and 120 h, respectively. Fecal marker excretion data were fitted using two-compartment mathematical age-dependent/age-independent (Gn-->G1) models. Inclusion of concentrate in the diet (SC) increased (P < 0.05) apparent total tract digestibility of dietary DM, OM and N. Digestibility of fiber fractions, NDF and ADF, was lower (P < 0.01 and P < 0.05, respectively) for SC compared with AS. The heavy particles had higher (P < 0.01) indigestible NDF and lower (P < 0.01) N concentration than LP. Particles from the HP pool passed from the rumen more rapidly (P < 0.01) than particles from LP (0.044 and 0.019 h(-1), respectively). Diet had no effect on particle rate of disappearance or pool size in the rumen. Across diets, pool size of LP was consistently larger (P < 0.05) than that of HP. Diet had no effect on total tract mean retention time (MRT) of LP or HP. Total tract MRT of LP was greater (P < 0.05) than MRT of HP (59.6 vs. 49.0 h, respectively). Results from this study support the hypothesis that functional specific gravity is an important factor determining the rate of outflow and residence time of feed particles within the reticulo-rumen and total digestive tract. Our data indicate that digesta particles with functional specific gravity greater or less than 1.02 have different composition and flow characteristics. Heavier particles contain more indigestible fiber and less N and are likely depleted of substrate available for microbial fermentation, are smaller in size, and have a higher passage rate/shorter retention time in the digestive tract than lighter particles.

Selective digesta retention and coprophagy in Brandt's vole (Microtus brandti).

Digestive performance, gut morphology and rate of digesta passage were measured in Brandt's voles (Microtus brandti) offered pelleted diets of low (25% neutral-detergent fibre) and high (38%) fibre content. Digestion coefficients of dry matter, crude fat, crude protein, energy and fibre were all significantly lower on the higher fibre diet. Although not significantly higher, dry matter intakes were more than maintained when extra cellulose was included in the diet, so that intakes of digestible energy were only 22% lower on the higher fibre diet. Total length and total gut tissue weight increased significantly, and the length and tissue weight of the caecum, proximal colon, and distal colon were significantly greater on the higher fibre diet as well. Total tract mean retention time (MRT) of a solute marker (Co-EDTA) was significantly greater than that of a particle marker (Cr-cell walls) on the lower fibre diet, and in the same direction on the higher fibre diet. The ratio of solute to particle MRTs (the solute/particle differential retention ratio) was 1.45 on the lower fibre diet and 1.19 on the higher fibre diet. There were no significant differences in marker MRTs between diets. Examination of marker concentrations in the stomach, small intestine, caecum and colon of voles killed at 0.5-h intervals after a pulse dose of Co-EDTA indicated that the marker was recycled to the stomach by coprophagy. Thus, as in other microtine rodents, an increase in gut capacity, selective digesta retention and recycling of digesta via coprophagy enables Brandt's voles to utilise diets of higher fibre content than may be expected for such a small (45 g) mammalian herbivore.

Grass Hay as a Supplement for Grazing Cattle II. Ruminal Digesta Kinetics

This study evaluated the effects of supplementing a diet of range hay (5.7% crude protein, 68% NDF) with grass hay from subirrigated meadows (16.5% crude protein, 53.5% NDF), or with a 70% soybean meal:30% wheat grain supplement (40% crude protein) on intake and ruminal digesta kinetics. Twelve ruminally fistulated steers were assigned to 3 treatments (4 steers/treatment) at 2 levels of intake. Treatments were: control, range hay; range hay supplemented with meadow hay (meadow hay was 20% of intake); and range hay supplemented with soybean meal:wheat supplement (supplement was 8% of intake). Intake levels were: ad libitum and equal intake (1.5% of body weight). Range hay was Yb-labeled, and meadow hay and soybean meal:wheat supplements were Er-labeled to measure passage. Intake and digestibility of range hay was not affected by supplementation (P > 0.05). During ad libitum intake, total intake (range hay + supplement) was greater (P > 0.05) for supplement treatments than for the control. No supplement treatment X level of intake interactions were detected (P > 0.05). Total digestibility (range hay + supplement) was greater (P 0.05) for control and meadow hay treatments. Ruminal passage rate (% hour-1), total tract mean retention time, and intestinal transit time of range hay did not differ among treatments (P > 0.05), but ruminal passage rate, total tract mean retention time, and intestinal transit time were greater (P < 0.01) with ad libitum than equal intake. We conclude that a meadow hay supplement produced similar effects on ruminal kinetics and intake of range hay as a soybean meal:wheat supplement.

Ermittlung der passage zweier marker im verdauungstrakt von ochsen mit hilfe unterschiedlicher schätzverfahren: Einfluss des ernährungsniveaus

An sechs ausgewachsenen, mit Pansennstein versehenen Ochsen wurde der Einfluß des Ernährungsniveaus auf die Passage des Verdauungsbreis aus dem Reticulorumen und durch den gesamten Verdauungstrakt untersucht. Die Tiere erhielten eine gemischte Ration, die in der DM im Mittel aus 43 % Grassilage, 25 % Maissilage, 30 % Konzentratfutter und 2 % Mineralfutter bestand und bei drei Ernährungsniveaus vorgelegt wurde: Erhaltungsbedarf und 1,5facher sowie 2facher Erhaltungsbedarf. Gefüttert wurde 2mal täglich, ab 7 Uhr und ab 19 Uhr. Die Versuchsanordnung entsprach einem doppelt besetzten 3×3 lateinischen Quadrat mit Versuchsperioden von 21 Tagen. Zu Beginn jeder Versuchsperiode erhielten die Tiere Einmaldosen der Marker Titan(IV)‐oxid (TiO2) mit dem Konzentratfutter und Cr‐EDTA als unverdünnte Lösung direkt in den Pansen. Kotproben wurden nach der Markergabe rektal über 120 h hinweg entnommen. Passageparameter wurden mit Hilfe unterschiedlicher Schätzverfahren ermittelt, wobei ein monoexponentielles und ein biexponentielles Modell, Modelle mit Gamma‐Zeitabhängigkeit sowie ein Modell, in dem die mittlere Verweildauer des Markers im gesamten Verdauungstrakt als Mittelwert aller Punkte der Marker‐Exkretionskurve berechnet wird, verwendet wurden. Mit steigendem Ernährungsniveau nahm die Passagerate von TiO2 aus dem Reticulorumen zu, die mittlere Verweildauer im gesamten Verdauungstrakt nahm ab. Die Ergebnisse der unterschiedlichen Modellansätze stimmten mit wenigen Ausnahmen gut überein. Außerdem zeigte sich eine gute Übereinstimmung zwischen den Ergebnissen der TiO2‐Passage und den Werten, die andere Versuchsansteller für die Passage kleiner, prinzipiell passagefähiger Teilchen bei ähnlichen Rationstypen ermittelten. Auch für Cr‐EDTA nahm die Passagerate aus dem Reticulorumen mit steigendem Ernährungsniveau zu, die mittlere Verweildauer im Reticulorumen und im gesamten Verdauungstrakt nahm ab. Es zeigten sich jedoch Differenzen zwischen den Modellansätzen mit oder ohne Zeitabhängigkeit. Die Anpassung an den Kurvenverlauf der Cr‐EDTA‐Ausscheidung mit dem Kot war bei den Modellen mit Gamma‐Zeitabhängigkeit unbefriedigend. Für beide Marker ergaben alle verwendeten Modelle übereinstimmend eine deutliche Beschleunigung der Passage aus dem Reticulorumen bzw. eine deutliche Verkürzung der Verweildauer im Reticulorumen und im gesamten Verdauungstrakt, wenn das Ernährungsniveau von der Deckung des Erhaltungsbedarfes auf das 1,5fache des Erhaltungsbedarfes angehoben wurde.

Ermittlung der passage eines markers im verdauungstrakt von milchkühen mit hilfe unterschiedlicher schätzverfahren: Einfluss von laktationsstadium, fütterungsniveau und rationszusammensetzung

An 12 Milchkühen wurde der Einfluß von Laktationsstadium, Fütterungsniveau und Rationszusammensetzung auf die Passage des Verdauungsbreis aus dem Reticulorumen untersucht. Es wurden gemischte Konzentratfutter: Rauhfutter‐Rationen verfüttert, wobei die Rauhfutterkomponenten aus Maisganz‐pflanzensilage und extensiv bzw. intensiv produzierter Grassilage im Verhältnis 40: 60 (Frischsubstanzbasis) bestanden und das durchschnittliche Konzentratfutter: Rauhfutter‐Verhältnis der Rationen 34: 66 in der Trockensubstanz betrug. Als Marker wurde Titan(IV)‐oxid (TiO2) eingesetzt, dessen Konzentration im Kot nach oraler Verabreichung über 120 h hinweg ermittelt wurde. Probenahmen erfolgten in vier Untersuchungszeiträumen (Perioden) ‐ ante partum (1 Periode) und in der ersten Laktationshälfte (3 Perioden) ‐, die jeweils einen bestimmten physiologischen Zustand charakterisierten. Die Fütterung der Tiere erfolgte leistungsgerecht mit durchschnittlichen Trockensubstanzaufnahmen von 12,0; 16,8; 22,6 und 21,2 kg in den jeweiligen Untersuchungszeiträumen. Passageparameter wurden mit Hilfe unterschiedlicher Schätzverfahren ermittelt, wobei ein Modell mit Gamma‐Zeitabhängigkeit (G4G1), ein exponentielles Modell sowie ein Modell, in dem die mittlere Verweildauer des Markers im gesamten Verdauungstrakt als Mittelwert aller Punkte der Marker‐Exkretionskurve berechnet wird, verwendet und verglichen wurden. Die Ergebnisse zeigten eine deutliche Beschleunigung der Passage des Markers aus dem Reticulorumen von ante partum nach post partum. Zwischen G4G1 und dem Modell, das auf die Verwendung des Mittelwertes Bezug nimmt, zeigte sich eine gute Übereinstimmung. Dagegen war die Übereinstimmung zwischen G4G1 und dem exponentiellen Modell schlechter. Effekte von Periode und Ration waren post partum nur für die Passagerate aus dem und für die mittlere Verweildauer im schnellen Kompartiment (beide geschätzt nach G4G1) nachzuweisen. TiO2 scheint als externer Marker zur Ermittlung von Passageraten gut einsetzbar zu sein, wobei die Größenordnung der Werte im Bereich der Passage von Konzentratfutterteilchen liegen dürfte.

Effects of four cereal grains on intake and ruminal digestion of harvested forage by beef steers

Effects of grain supplements on intake and digestion of roughage diets have been studied extensively, but studies comparing these effects among different grains are limited. Our experiment compared the effects of four cereal grains on roughage intake and ruminal digestion. Five separately penned ruminally cannulated beef steers (average body weight (BW) 194 kg) were used in a 5 × 5 Latin square design; treatments included prairie hay, or prairie hay plus supplemental barley, corn, sorghum or wheat. Each grain was dry rolled and fed to provide 0.25% BW as starch to a basal diet of prairie hay (in vitro organic matter digestibility, 56 g 100 g −1; crude protein, 10.8 g 100 g −1 of organic matter). Urea was added to grains to ensure that supplements were isonitrogenous. Grain supplementation did not affect ( P > 0.10) hay organic matter intake, although digestible organic matter intake was increased ( P < 0.10) by supplementation. Ruminal pH was not affected ( P > 0.10) by grain supplementation. Ruminal ammonia-nitrogen was increased ( P < 0.10) by grain supplements containing urea (barley, corn, and sorghum). Ruminal fluid volume and dilution rate was not affected ( P > 0.10) by grain supplementation, nor were particulate passage rate, ruminal or intestinal retention time, or gastrointestinal dry matter fill. Total tract mean retention time was decreased ( P < 0.10) by barley, corn and wheat supplementation, but unaffected ( P > 0.10) by sorghum. A treatment × sampling time interaction ( P < 0.05) was detected for proportions of ruminal acetate and propionate. Acetate was decreased ( P < 0.01) by barley and increased ( P < 0.01) by sorghum. 4 h after supplementation. At 8 h after supplementation, wheat decreased ( P < 0.10) acetate proportions, while sorghum increased acetate proportions ( P < 0.01). Propionate proportions were not affected ( P > 0.10) by treatments. Wheat supplementation increased ( P < 0.01) ruminal butyrate at 2 and 12 h after supplementation, but sorghum decreased butyrate proportions at 2, 8 and 12 h after supplementation. Barley increased ( P < 0.10) total volatile fatty acid (VFA) concentrations at 4 h after supplementation, but VFA concentrations were not affected by other grains. Grain supplementation increased ( P < 0.10) in sacco organic matter disappearance of prairie hay at 48 h of incubation. We conclude that grain supplementation, to provide 0.25% of BW as starch, did not affect hay intake adversely, and slightly increased in sacco digestion of hay organic matter. More readily fermentable grains (barley and wheat) affected ruminal VFA proportions and concentrations.

Effect of Forage Source on Retention of Digesta Markers Applied to Corn Gluten Meal and Brewers Grains for Heifers

Effect of forage source on retention time of dietary protein supplements in the rumen was measured, and solid and liquid markers of digesta passage were compared. Two markers for liquid, two for each of the forages, and two for each of the supplemental proteins were compared for estimating retention time. Eight Holstein heifers were allocated to a single-reversal design with two periods of 29 d each. Heifers were fed either alfalfa hay or corn husks and leaves combined with one of two resistant protein sources: corn gluten meal or wet brewers grains. Average rumen liquid retention times, measured with Co-EDTA or Cr-EDTA, were similar (16.2 to 16.9h). Liquid retention times differed when alfalfa or corn residue was fed (14.1 and 18.9h, respectively). Rumen retention times were similar for Sm and Ce (24.9 to 26.3h) and across markers for forage sources (25.1 to 26.1h). Total tract mean retention time was higher for corn residue than for hay (57.8 vs. 48.8h). Rumen retention times for La and Yb (27.1 and 26.0h) applied to protein sources were similar and were not different when applied to corn gluten meal or brewers grains (26.3 and 26.8h). Forage source did not have an effect on the retention time of protein supplements. Low daily DMI of 2.22 and 1.91% of BW for hay and corn residue diets explain the rather long retention times of the protein supplements. Both Co-EDTA and Cr-EDTA were affective as liquid phase markers.