Fecal Marker Concentrations Research Articles

Passage kinetics of 13C-labeled corn silage components through the gastrointestinal tract of dairy cows

Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants but knowledge on feed type and feed component specific passage rates are largely lacking. This study describes the use of carbon stable isotopes (13C) to assess component-specific passage kinetics of 6 intrinsically 13C-labeled corn silages varying in quality (2 cultivars×3 maturity stages) in a 6×6 Latin square design using 6 rumen-fistulated lactating dairy cows. An increase in maturity increased starch and decreased neutral detergent fiber and acid detergent fiber contents of corn silages. Passage kinetics were assessed for an external (chromium mordanted fiber; Cr-NDF) and an internal marker (13C isotopes) collected in feces and omasal digesta. The best fit was obtained with a deterministic multicompartmental model compared with stochastic Gn and GnG1 models with increasing order of age dependency (n=1 to 5) for both sampling sites. The Cr-NDF marker yielded higher rumen fractional passage rates (K1) than did 13C in the dry matter (13CDM) in feces (0.042/h vs. 0.023/h). Omasal marker excretion patterns support the conclusions based on conventional fecal marker excretions. Component-specific passage was assessed for acid detergent fiber (13CADF) in feces and for starch (13CST) in omasal digesta. The fractional passage rate based on fecal 13CDM and 13CADF did not differ. Omasal 13CST provided higher K1 values (0.042/h) than omasal 13CDM (0.034/h) but lower values than omasal Cr-NDF (0.051/h). Fractional passage rates from the proximal colon-cecum (K2) based on fecal marker concentrations showed trends similar to K1, with Cr-NDF providing a value (0.425/h) more than twice as high as that of 13CDM (0.179/h) and 13CADF (0.128/h). Total mean retention time in the gastrointestinal tract was approximately double for 13CDM (64.1h) and 13CADF (77.6h) compared with Cr-NDF (36.4h). Corn silage quality did not affect any of the estimated passage kinetic parameters. In situ fractional degradation rates did not differ among corn silages, except for a decreased fractional degradation rate of starch with advancing maturity. Results indicate that isotope labeling allows assessment of component-specific passage kinetics of carbohydrate fractions in corn silage.

Fecal pathogen pollution: sources and patterns in water and sediment samples from the upper Cook Inlet, Alaska ecosystem

Fecal pathogens are transported from a variety of sources in multi-use ecosystems such as upper Cook Inlet (CI), Alaska, which includes the state's urban center and is highly utilized by humans and animals. This study used a novel water quality testing approach to evaluate the presence and host sources of potential fecal pathogens in surface waters and sediments from aquatic ecosystems in upper CI. Matched water and sediment samples, along with effluent from a municipal wastewater treatment facility, were screened for Salmonella spp., Vibrio spp., Cryptosporidium spp., Giardia spp., and noroviruses. Additionally, Bacteroidales spp. for microbial source tracking, and the fecal indicator bacteria Enterococcus spp. as well as fecal coliforms were evaluated. Overall, Giardia and Vibrio were the most frequently detected potential pathogens, followed by Cryptosporidium and norovirus, while Salmonella was not detected. Sample month, matrix type, and recent precipitation were found to be significant environmental factors for protozoa or host-associated Bacteroidales marker detection, whereas location and water temperature were not. The relative contribution of host-associated markers to total fecal marker concentration was estimated using a Monte Carlo method, with the greatest relative contribution to the Bacteroidales marker concentration coming from human sources, while the remainder of the universal fecal host source signal was uncharacterized by available host-associated assays, consistent with wildlife fecal sources. These findings show how fecal indicator and pathogen monitoring, along with identifying contributing host sources, can provide evidence of coastal pathogen pollution and guidance as to whether to target human and/or animal sources for management.

Passage kinetics of concentrates in dairy cows measured with carbon stable isotopes

Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants, but knowledge on feed-specific fractional passage is largely lacking. Commonly applied tracer techniques based on externally applied markers, such as chromium-mordanted neutral detergent fibre (Cr-NDF), have been criticised for behaving differently to feed particles. This study describes the use of the carbon stable isotope ratio (13C : 12C) as an internal digesta marker to quantify the fractional passage rate of concentrates through the digestive tract of dairy cows. In a crossover study, five dairy cows were fed low (24.6%) and high (52.6%) levels of concentrates (dry matter (DM) basis) and received a pulse-dosed Cr-NDF and 13C isotopes. The latter was administered orally by exchanging part of the dietary concentrates of low 13C natural abundance with a pulse dose of maize bran-based concentrates of high 13C natural abundance. Fractional passage rates from the rumen (K1) and from the large intestine (K2) were determined from faecal marker concentrations of Cr-NDF and of 13C in the DM (13C-DM), NDF (13C-NDF) and neutral detergent soluble (13C-NDS). No differences in K1 estimates were found for the two concentrate levels fed but significant differences between markers (P<0.001) were observed. Faecal Cr-NDF excretions gave lower K1 estimates (0.037–0.039/h) than 13C-DM (0.054–0.056/h) and 13C-NDF (0.061–0.063/h). The 13C-NDS was calculated by the difference of 13C in the DM and NDF, and K1 values (0.039–0.043/h) were comparable to Cr-NDF. Total mean retention time was considerably higher for Cr-NDF (40.9–42.0 h) as compared to 13C-DM and 13C-NDF (32.0–33.5 h; P<0.001). The accuracy of the curve fits for Cr-NDF and 13C-DM and 13C-NDF was overall good (mean prediction error of 9.9–13.9%). Fractional passage rate of Cr-NDF was comparable to studies where this marker was assumed to represent the fractional passage of roughages. However, K1 estimates based on the 13C : 12C ratio varied considerably from studies based on external markers. Our results suggest that the use of 13C isotopes as digesta passage markers can provide feed component-specific K1 estimates for concentrates and provides new insight into passage kinetics of NDF from technologically treated compound feed.

Development and evaluation of empirical equations to predict ruminal fractional passage rate of forages in goats

SUMMARYThe objectives of the present paper were to develop and evaluate empirical equations to predict fractional passage rate (kp) of forages commonly fed to goats using chemical composition of the diet and animal information. Two databases were created. The first (development database) was assembled from four studies that had individual information on animals, diets and faecal marker concentrations over time (up to 120 h post-feeding); it contained 54 data points obtained from Latin square designs. The second (evaluation database) was built using published information gathered from the literature. The evaluation database was comprised of five studies, containing 39 data points on diverse types of diets and animal breeds. The kp was estimated using a time-dependent model based on the Gamma distribution with at least two and up to 12 (rumen)+one (post-rumen) compartments (i.e. G2G1–G12G1) developed from the development database. Statistical analyses were carried out using standard regression analysis and random coefficient model analysis to account for random sources (i.e. study). The evaluation of the developed empirical equation was conducted using regression analysis adjusted for study effects, concordance correlation coefficient and mean square error of prediction. Sensitivity analyses with the developed empirical equation and comparable published equations were performed using Monte Carlo simulations. The G2G1 model consistently had lower sum of squares of errors and greater relative likelihood probabilities than other GnG1 versions. The kp was influenced by several dietary nutrients, including dietary concentration or intake of components such as lignin, neutral detergent fibre (NDF), hemicellulose, crude protein (CP), acid detergent fibre (ADF) and animal body weight (BW). The selected empirical equation, adjusted for study effects, ($kp_{/{\rm h}} = 0{\cdot}00161 \times {\rm NDF}_{{\rm g/kg\,BW}}^{1{\cdot}503 \pm 0{\cdot}371} \times {\rm e}^{(0{\cdot}022 \pm 0{\cdot}0097 \times {\rm BW}_{{\rm kg}} - 0{\cdot}00375 \pm 0{\cdot}0013 \times {\rm NDF}_{{\rm g/kg \ DM}} )} $) had an R2 of 0·623 and root of mean square error (RMSE) of 0·0122/h. The evaluation of the adequacy of the selected equation with the evaluation database indicated no systematic bias (slope not different from 1), but a low accuracy (0·33) and a persistent mean bias of 0·0129/h. The sensitivity analysis indicated that the selected empirical equation was most sensitive to changes in dry matter intake (DMI, kg/d), BW(kg) and NDF (g/kg dry matter) with standardized regression coefficients of 0·98, −0·43 and −0·32, respectively. The sensitivity analysis also indicated that the greatest forage kp in goats is likely to be c. 0·0569/h. The comparison with a previously published empirical equation containing data on cattle, sheep and goats, suggested that the distribution of the present empirical equation, adjusted for mean bias, is wider and that kp of goats might be similar to cattle and sheep when fed high amounts of forage under confinement conditions.

Ytterbium oxide has the same accuracy as chromic oxide for estimating variations of faecal dry matter output in dairy cows fed a total mixed ration at two feeding levels

Daily herbage intake by ruminants at grazing can be estimated from faecal output and herbage digestibility. Chromic oxide has long been used as an external marker to estimate faecal dry matter (DM) output. The aim of this experiment was to determine the performance of ytterbium oxide compared to chromic oxide as an external marker for estimating variations of faecal DM output in dairy cows. Both markers were compared on eight Prim’Holstein lactating dairy cows, of which four were fistulated. Cows were offered a total mixed diet based on maize silage either at 100% or 70% of ad libitum DM intake, according to a single 2 × 2 reversal design with 2 experimental periods of 3 weeks. Faecal recovery of markers was determined over the last five days of each period by total faecal collection or by faecal sampling only during milking times. The between-day and the within-day variability of faecal marker concentrations were also investigated, as well as the between-day variability of faecal marker concentrations during the transition between periods 1 and 2. Both markers over-estimated the actual faecal DM output due to an incomplete faecal recovery. The average faecal recovery was slightly greater for Yb than for Cr (0.93 vs. 0.89). Faecal recovery of Yb and Cr was unaffected by feeding level irrespective of the faecal collection method. Ytterbium showed similar between-day and within-day variability of faecal concentration as Cr during the experiment (steady-state period), and similar between-day variability of faecal concentration as Cr during the transition period (non steady-state period). We conclude that ytterbium oxide used as a digestive marker seems to have the same accuracy as chromic oxide for estimating daily faecal DM output variations in dairy cows fed a total mixed ration, at low and high feeding level.

Evaluation of very long-chain fatty acids and n-alkane epicuticular compounds as markers for estimating diet composition of sheep fed heathland vegetation species

Application of very long-chain fatty acids (VLCFA) as an alternative or a complement to the alkane markers to estimate diet composition of sheep offered six different diets was evaluated. Twenty-four adult crossbred sheep were housed in metabolic crates and fed with diets composed of different proportions of herbaceous ( Lolium perenne and Trifolium repens) and woody species ( Erica spp., Calluna vulgaris and Ulex gallii). Diet composition was estimated from VLCFA (i.e., C 22–C 34) and alkane (i.e., C 25–C 33) concentrations in diet and faeces, by least-squares procedures, considering the plant species effectively offered to the animals (C1) or these plant species plus feeds that were not part of the diets but were available in the field at each experimental period (C2). Prior to this, faecal VLCFA and alkane concentrations were uncorrected for incomplete faecal recovery (FC0), corrected using recovery data for each individual ewe (FC1), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC2), or corrected using mean recovery rate across all experimental diets (FC3). For all diet components, total VLCFA concentrations were higher ( P<0.01) than those observed for alkanes, with a predomination of even-chain ( P<0.001) over odd-chain. Faecal recovery was incomplete and tended to increase with carbon-chain length in a curvilinear ( P<0.001) fashion for the even-chain VLCFA, and a linear ( P<0.001) one for odd-chain VLCFA and alkanes. Diet composition had an effect ( P<0.001) on faecal recovery of both markers. Estimates of diet composition obtained using alkanes alone were more accurate ( P<0.05) than those obtained with VLCFA alone while their combination resulted in an improvement ( P<0.05) of the accuracy. Estimates obtained when considering plant species offered effectively to the animals were more accurate ( P<0.001) than those obtained when considering more plant species as possible diet components. In general, use of faecal marker concentrations corrected with FC2 and FC3 provided equally accurate estimates of diet composition, indicating that an overall recovery data can be applied to these markers in grazing studies without losing accuracy in the estimation. Although the use of alkanes resulted in more accurate estimates of diet composition, results obtained in this study showed that VLCFA can be useful markers for studying diet selection of sheep grazing on shrubland vegetation communities. However, a suitable adjustment of their faecal concentrations prior to their application is recommended. It is also concluded that use of VLCFA in combination with alkanes could result in more accurate estimates of diet composition.

Concentrations of host-specific and generic fecal markers measured by quantitative PCR in raw sewage and fresh animal feces

We measured the concentrations of four host-specific (human, dog, cow, and horse Bacteroidales), four generic fecal (16S total Bacteroidales and Escherichia coli, 23S Enterococcus and uidA E. coli,) and two universal bacterial (16S universal and rpoB universal) DNA targets by qPCR in raw sewage and pooled fecal samples from dogs, cows, horses, and Canada Geese. A spiking protocol using the non-fecal bacterium Pseudomonas syringae pph6 was developed to estimate the recovery of DNA from fecal and environmental samples. The measured fecal marker concentrations were used to calculate baseline ratios and variability of host-specific to generic indicators for each host type. The host-specific markers were found in high concentrations (8–9 log 10 copies/g dry wt.) in their respective hosts' samples, which were equal to or greater than the concentrations of generic E. coli and Enterococcus markers, lending support to the use of host-specific and generic Bacteroidales as sensitive indicators of fecal pollution. The host-specific markers formed a consistent percentage of total Bacteroidales in target host feces and raw sewage, with human-specific comprising 82%, dog-specific 6%, cow-specific 4% and horse-specific 2%. Based on this limited data set, the measurement of host-specific indicators by qPCR has several promising applications. These applications include determining the percentage of total Bacteroidales contributed by a specific host type, using the ratios of host-specific markers to E. coli or Enterococcus to estimate the contribution of each source to these regulated fecal indicator bacteria, and estimating the mass of feces from each host type in environmental samples.

Assessment of very long-chain fatty acids as complementary or alternative natural fecal markers to n-alkanes for estimating diet composition of goats feeding on mixed diets1

This study aimed to assess the use of very long-chain fatty acids (VLCFA) as an alternative or a complement to n-alkane markers for estimation of diet composition of goats fed 7 different diets, composed of different proportions of herbaceous (Lolium perenne and Trifolium repens) and heathland woody species (Erica umbellata, Erica cinerea, Calluna vulgaris, Erica arborea, and Ulex gallii), in a metabolism study. Diet composition was estimated from VLCFA (i.e., C(22) to C(34)) and alkane (i.e., C(25) to C(33)) concentrations in diet and feces, by least squares procedures. For all plant species VLCFA concentrations were greater than their alkane concentrations, especially for the herbaceous species and U. gallii. In general, fecal recovery of both markers was incomplete and increased in a curvilinear (P < 0.001) fashion with carbon-chain length. The plants comprising the diets had a significant effect (P < 0.001) on fecal recovery of VLCFA and alkanes. Diet composition estimates based on VLCFA alone were less accurate (P = 0.013) than those obtained using alkanes alone. Combination of VLCFA and alkane data resulted in the most accurate (P < 0.05) estimates, indicating an increase on the discriminatory power among plant species. Use of uncorrected fecal marker concentrations provided the poorest estimates of diet composition, and use of individual recovery data and mean fecal recovery data of the dietary treatment yielded the most accurate ones. Results obtained in this study show that VLCFA have potential to be used as diet composition markers along with alkanes.

The use of even-chain alkanes sprayed onto herbage as rate of passage markers in goats

An experiment was conducted with Saanen goats fed fresh grass ad libitum to compare 51Cr-mordanted fibre and even-chain alkanes sprayed onto either grass leaves or stems to estimate faecal output, total mean retention time (TMRT) and parameters obtained from faecal marker concentration curves, such as k 1 (slow rate of passage), k 2 (fast rate of passage) and transit time (TT). 51Cr-mordanted grass showed the lowest fractional rates of passage ( k 1 and k 2) and hence the largest value of TMRT. There were not significant ( P > 0.05) differences between even-chain alkanes sprayed onto leaves or stems for k 2, TT and TMRT, but k 1 estimates were higher ( P < 0.05) for stems than for sprayed leaves. Despite the marker used, TMRT values were negatively correlated with the level of dry matter intake ( r = − 0.81, − 0.80 and − 0.80 for 51Cr-mordanted fibre and even-chain alkanes adsorbed onto leaves or stems, respectively). Average faecal outputs estimated from faecal concentrations of 51Cr-mordanted fibre and even-chain alkanes were not different from the actual outputs but there were differences between markers in the accuracy of estimation. The highest mean square prediction error (MSPE) and the poorest correlation between observed and estimated faecal output values corresponded to even-chain alkanes adsorbed onto stems. Values estimated using 51Cr-mordanted fibre and even-chain alkanes adsorbed onto leaves were significantly correlated with faecal outputs ( r = 0.94 and r = 0.92, respectively), with MSPE being greater for the latter marker.

Effects of carrier matrix and dosing frequency on digestive kinetics of even‐chain alkanes and implications on herbage intake and rate of passage studies

AbstractAn experiment was carried out to investigate the digestive kinetics of various even‐chain alkanes adsorbed into different carrier matrices and to assess their potential use to estimate faecal output, herbage intake and rate of passage in goats. The carrier matrices (alkanes) tested were cellulose powder (C24 and C28 alkanes), paper bungs (C26 alkanes), Gilson paper filters (C30 alkanes) and shredded paper (C32 alkanes). Effects of carrier matrix and dosing frequency (once or twice daily) on diurnal fluctuations of faecal marker concentrations were simulated by modelling the faecal excretion curves of each marker. C32 alkanes adsorbed into shredded paper showed the longest transit time (TT) and the slowest fractional outflow rate from a fast compartment (k2) and consequently a greater total mean retention time (TMRT) than the other markers. In contrast, both C24 and C28 alkanes absorbed into cellulose powder showed the fastest k2 and the shortest TT and TMRT. Our results suggest that relative differences in rate of passage associated with different nutritional treatments can be investigated using even‐chain alkanes as rate of passage markers for comparative studies. Faecal outputs measured or estimated using C28, C30 or C32 alkanes as external markers were not significantly (P &gt; 0.05) different, but the accuracy of estimation was higher with C28 and C32 alkanes (r = 0.81 and 0.83 respectively). On average, faecal output was significantly (P &lt; 0.05) overestimated by 31% (SEM 9.4) and 35% (SEM 11.2) with C24 and C26 alkanes respectively. There were no significant (P &gt; 0.05) differences between observed and estimated herbage intakes when pairs C31/C30 and C33/C32 were used, this latter pair of alkanes giving the best prediction. With the other alkane pairs (C25/C24, C27/C26 and C29/C28), estimates were biased, although actual and predicted values were significantly (P &lt; 0.05) correlated. The simulation study revealed that, when markers were dosed twice a day, there were no significant (P &gt; 0.05) differences between even‐chain alkanes in the amplitude of the diurnal fluctuation of their faecal concentrations. However, when the marker administration was as a single dose per day, C32 alkane absorbed into shredded paper resulted in the narrowest range of variation, with no significant differences among the other carrier matrices. Copyright © 2004 Society of Chemical Industry

Preoperative nurse-patient encounter: interview or conversation?

Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants but knowledge on feed type and feed component specific passage rates are largely lacking. This study describes the use of carbon stable isotopes (13C) to assess component-specific passage kinetics of 6 intrinsically 13C-labeled corn silages varying in quality (2 cultivars × 3 maturity stages) in a 6 × 6 Latin square design using 6 rumen-fistulated lactating dairy cows. An increase in maturity increased starch and decreased neutral detergent fiber and acid detergent fiber contents of corn silages. Passage kinetics were assessed for an external (chromium mordanted fiber; Cr-NDF) and an internal marker (13C isotopes) collected in feces and omasal digesta. The best fit was obtained with a deterministic multicompartmental model compared with stochastic Gn and GnG1 models with increasing order of age dependency (n = 1 to 5) for both sampling sites. The Cr-NDF marker yielded higher rumen fractional passage rates (K1) than did 13C in the dry matter (13CDM) in feces (0.042/h vs. 0.023/h). Omasal marker excretion patterns support the conclusions based on conventional fecal marker excretions. Component-specific passage was assessed for acid detergent fiber (13CADF) in feces and for starch (13CST) in omasal digesta. The fractional passage rate based on fecal 13CDM and 13CADF did not differ. Omasal 13CST provided higher K1 values (0.042/h) than omasal 13CDM (0.034/h) but lower values than omasal Cr-NDF (0.051/h). Fractional passage rates from the proximal colon-cecum (K2) based on fecal marker concentrations showed trends similar to K1, with Cr-NDF providing a value (0.425/h) more than twice as high as that of 13CDM (0.179/h) and 13CADF (0.128/h). Total mean retention time in the gastrointestinal tract was approximately double for 13CDM (64.1 h) and 13CADF (77.6 h) compared with Cr-NDF (36.4 h). Corn silage quality did not affect any of the estimated passage kinetic parameters. In situ fractional degradation rates did not differ among corn silages, except for a decreased fractional degradation rate of starch with advancing maturity. Results indicate that isotope labeling allows assessment of component-specific passage kinetics of carbohydrate fractions in corn silage.

Granulated polyamide as external marker to estimate total faecal excretion of grazing cattle in extensive management systems

Granulated polyamide (PA) was tested for use as an external marker to estimate faecal DM (FDM) excretion of Zebu cattle (Bos indicus). The study was conducted in Mali, using seven and eighteen animals respectively in four field trials and six indoor experiments. Cattle ate fresh or dry pasture vegetation and half the animals were additionally supplemented with crop byproducts. Gelatine capsules containing 35, 40 or 45 g PA were administered orally at 12 h intervals. Estimates of FDM were based on the average marker concentration in faeces and were correlated with the actual excretion measured by total faecal collection. The pre-measurement period required to establish equilibrium for regular marker dosing was determined at 4 d. Except for diets with a N content of less than 9.26 g/kg organic matter, marker recovery averaged 98.1 (SE 0.93)% (n 62), and was not influenced by diet composition and the quantity of feed ingested (P > 0.05). Estimates of FDM based on average PA concentrations in faecal samples were correlated to the actual excretion with r 0.98 (n 62; P < or = 0.001). Since the PA concentration in individual faecal grab-samples is not correlated with either sample mass or sampling time, accurate estimates of FDM require a grab-sampling schedule that covers the 24 h day. However, estimates of FDM were found to be acceptable if calculations are based on the average PA concentration in the sub-total of samples collected during the day or during night respectively (r 0.95, n 29; P < or = 0.001 in both cases). It is concluded that the use of PA marker is a simple and inexpensive method resulting in reliable estimates of FDM. Since sophisticated analytical procedures are not required to recover PA in faecal samples, the marker is particularly suitable for application in extensive grazing systems and in studies conducted in less-developed countries.

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.

The effects of diffusion and viscosity on ruminant faecal excretion of markers in a simple compartmental model.

Using equations obtained in a previous analysis, results are computed numerically which illustrate the effects of diffusion and viscosity on faecal excretion patterns of markers in ruminants. Results are first given for plug flow, a velocity gradient produced by viscosity, and diffusion, each mechanism operating alone. Plug flow gives a period during which no marker appears in the faeces, then a sharp increase in faeces marker concentration, followed by rapid washout. A velocity gradient gives a more gradual appearance of marker in the faeces followed by a slower washout. Diffusion alone (although not realistic for ruminant marker kinetics) can give early appearance of marker followed by slow washout. Combining diffusion with a velocity gradient produced by viscosity can give a range of behaviour, depending on the effective diffusion coefficient, D'; an approximate method is used to compute these solutions. Because plug flow with no velocity gradient plus diffusion gives results similar to convective flow with a velocity gradient plus diffusion, we believe it will not be possible to determine the main mechanisms defining marker outflow patterns from observations of marker kinetics alone, and more detailed investigations will be needed. Although estimates of quantities such as mean transit time are unaffected by detailed mechanism, the interpretations of measures such as sigmoidicity, sharpness of the faecal marker concentration v. time curve, and length and nature of the washout tail are highly dependent on mechanism.

Estimating forage intake and energy requirements of free-ranging wapiti (Cervus elaphus)

A single dose marker method was calibrated to estimate intakes of pasture forage by wapiti. Each animal was offered 250 g of alfalfa–barley pellets labeled with chromic oxide (Cr2O3), and freshly voided fecal samples were collected before and for 6–7 days after administration. Dry fecal output was calculated by dividing the marker dosage by the average fecal marker concentration. Feed intake was then calculated from fecal output and feed digestibility as determined by total fecal collection or the ratio of acid-insoluble ash in feed and feces. The concordance of the marker estimate with measured feed intake was tested on penned wapiti fed alfalfa–barley pellets or herbage. On pasture, the marker method was compared with intakes estimated by the bite-count method. As an additional check, data from pen and field studies were pooled to establish the relationship between metabolizable energy intake and body-weight gain. The single dose marker method provided a practical way to assess feed intake of free-ranging animals. Metabolizable energy requirements for maintenance of live weight were 572 kJ/W0.75 for penned wapiti in winter and 936 kJ/W0.75 for wapiti on summer pasture. Tissues mobilized during winter provided 26 kJ/g, and metabolizable energy requirement per unit liveweight gain was 39 kJ/g on summer pasture.

Technical note: effectiveness of different methods of continuous marker administration for estimating fecal output

Six ruminally fistulated crossbred steers (BW = 369 kg) were used in a randomized complete block experiment to test the efficacy of continuous-infusion pumps and controlled-release boluses for administering external markers to predict fecal output. Steers, limit-fed chopped alfalfa hay at 2% of BW daily, were fitted with continuous-infusion pumps that administered Co-EDTA and YbCl3 solutions intraruminally. In addition, a controlled-release bolus containing Cr2O3 was inserted into the rumen of each steer. Fecal grab samples were taken every 6 h for 7 d during initial marker equilibration; after this period, fecal grab samples were taken every 3 h for 48 h to evaluate diurnal variation patterns. Steers were subsequently fitted with fecal bags for 7 d to allow total fecal collection. Grab samples also were taken during the total fecal collection period at 0600 (AM) and 1400 (PM). The marker X time effect was nonsignificant. Similarly, time of grab sampling (AM or PM) did not affect estimates of fecal output (P greater than .10), but the Cr2O3 bolus overestimated fecal output (P less than .05). Fecal marker concentrations during the 48-h profile showed little diurnal variation regardless of marker used. All markers equilibrated in the feces at approximately 100 to 120 h after initiating infusions. The continuous-infusion pumps evaluated were efficacious for administering markers for estimating total fecal output in limit-fed steers; however, the Cr2O3 boluses evaluated overestimated fecal output when the manufacturer's suggested release rate was used for fecal output calculations.

Evaluation of controlled release devices for administration of chromium sesquioxide using fistulated grazing sheep. 1. Variation in marker concentration in faeces

A group of 10 sheep grazed as a single flock; five were dosed with chromium sesquioxide (Cr2O3) using an experimental controlled release device, and five were dosed twice a day with gelatin capsules. Total faecal output was collected from each sheep over a period of 13 days, and in addition, a sample was taken twice daily from the rectum (grab sample). In a second experiment total faeces were collected every 2 h for 24 h. Total faecal output was compared with estimates of faecal output calculated from the quantity of Cr2O3 in the dose, and the concentrations in representative samples and in grab samples of faeces. An examination was made of the biases in the estimates from these two types of samples for the controlled release devices and for the gelatin capsules. Use of the controlled release devices significantly reduced circadian variation in the Cr2O3concentration in faeces, compared with twice daily dosing with gelatin capsules. Consequently variability was lower and biases in estimates of faecal output were relatively small. Once daily grab sampling from sheep with controlled release devices produced more reliable estimates of faecal output than twice daily sampling from sheep with gelatin capsules.

On using a double-exponential model for describing faecal marker concentration curves

A mathematical and numerical appraisal of the double-exponential model is presented, with particular reference to its ability to reproduce preset values of biological measures such as rumen and whole-tract mean retention times and faecal production rate. A complete, formal mathematical derivation is provided, with consideration given to a solution to the model when the two smallest rate constants are equal. It is concluded that any error introduced by using an approximation in deriving the double-exponential form is negligible in practice, and that the double exponential in logarithmic form is able to determine the relevant biological measures quite satisfactorily and speedily.

Fractional outflow of soyabean meal from the rumen of Chios lambs and Damascus kids

In earlier studies, results from incubation experiments were combined with measurements of outflow rates of small particles from the rumen to predict the extent of degradation of dietary protein in vivo (Orskov &amp; McDonald 1979). The degradability of a protein supplement was shown to decrease when fractional outflow rate increased (Orskov 1982). In a series of experiments, the factors affecting the fractional rates of outflow of dietary protein supplements from the rumen of sheep and lactating dairy cows were investigated (Agricultural Research Council 1984). In addition, outflow rate of soyabean meal from the rumen of dry and lactating Chios sheep and Damascus goats offered high concentrate diets was determined in recent studies (Hadjipanayiotou et al. 1988). Chromium-treated protein supplements were used to measure their outflow from the rumen using the marker concentration in faeces (Ørskov 1982). This paper reports outflow from the rumen of growing Chios lambs and Damascus kids offered concentrates ad libitum.