Marker Excretion Patterns Research Articles

Digestive physiology, resting metabolism and methane production of captive Indian crested porcupine (<i>Hystrix indica</i>)

Limited physiological measurements exist for the digestive physiology of porcupines. We measured CH4 emission in three captive Indian crested porcupines (Hystrix indica; 16.1 ± 2.7 kg) fed a diet of pelleted lucerne, and measured feed intake, digestibility, and digesta mean retention time (MRT) of a solute and three particle markers (<2, 10 and 20 mm). Marker excretion patterns suggested secondary peaks indicative of caecotrophy, with MRTs of 26.4 h for the solute and 31.5, 26.8 and 26.2 h for the three particle markers, respectively. At a dry matter intake of 58 ±10 g/kg body mass0.75/day, porcupines digested 49 and 35% organic matter and neutral detergent fibre, respectively, which is in the lower range of that expected for horses on a similar diet. The respiratory quotient (CO2/O2) was 0.91, the resting metabolic rate 274 kJ/kg body mass0.75/day, and CH4 emissions averaged at 8.16 l/day and 17.9 l/kg dry matter intake. Accordingly, CH4 yield was so high that it resembled that of a hypothetical ruminant of this body mass. The results are in accord with general understanding of hystricomorph rodent digestive physiology, and support recent findings that CH4 production may be more prominent in rodents than previously thought.

Digestive efficiency, digesta passage, resting metabolism and methane production in captive juvenile nutria (Myocastor coypus)

Although it is known that most herbivores produce methane (CH4), CH4 emissions in rodents are generally considered negligible and have rarely been measured in live animals. We measured CH4 emission in four captive juvenile nutria (Myocastor coypus) fed a diet of pelleted lucerne, as well as food intake, digestibility, and digesta mean retention time (MRT) of a solute and a particle marker. Marker excretion patterns revealed secondary peaks indicative of coprophagy, with MRTs of 30.2 ± 4.2 h and 24.2 ± 4.2 h for solutes and particles, respectively, and a resulting MRTsolute/MRTparticle ratio of 1.26 ± 0.07, which is still typical for a ‘mucus-trap’ colonic separation mechanism. At a dry matter intake of 28 ± 6 g kg body mass−0.75 d−1, the nutria digested organic matter and neutral detergent fibre at 59 ± 3% and 46 ± 3%, respectively, similar to what might be expected from horses on a diet with this fibre content. The respiratory quotient (CO2/O2) was 0.95 ± 0.02, the resting metabolic rate 266 ± 31 kJ kg body mass−0.75 day−1 and CH4 emissions averaged at 1.72 ± 0.17 L day−1 and 39.8 ± 11.3 L per kg dry matter intake; this at a CH4/CO2 ratio of 0.08 ± 0.04. Accordingly, methane yield was of a magnitude expected for a hypothetical ruminant of this body mass. While rodents’ CH4 contributions to global budgets might be low due to their low body size, this should not give rise to the assumption that CH4 production is not a relevant part of their digestive physiology.

Effect of different feeding regimes on cecotrophy behavior and retention of solute and particle markers in the digestive tract of paca (Cuniculus paca)

Many small herbivores practice cecotrophy - the ingestion of special feces enriched in microbial protein by colonic separation mechanisms (CSM). In digesta passage experiments, secondary marker excretion peaks in feces are considered indicative of marker-reingestion via cecotrophy, but corroboration by behavioral observation was lacking so far. The paca (Cuniculus paca), a Neotropical hystricomorph rodent, produces two different kinds of feces (hard and soft) and practices cecotrophy either directly (from the anus) or indirectly (from a pile of defecated feces, mostly when hard and soft feces are defecated together). To investigate effects of diet on cecotrophy, we monitored cecotrophy behavior and digesta passage marker excretion of solute and particle markers in four adult pacas, at constant food intake, on four diets varying in protein and fiber content. Marker excretion patterns suggested a ‘mucus-trap’ CSM typical for hystricomorph rodents, and showed secondary peaks of a similar time lag after cecotrophy as the primary marker peak after marker feeding. However, not every cecotrophy event was followed by a secondary marker peak. On higher fiber/lower protein diets, the number of cecotrophy bouts, the duration of cecotrophy, the number of secondary marker peaks and the difference between solute and particle marker retention increased, whereas the proportion of indirect cecotrophy decreased, indicating a higher degree of digesta phase separation on these diets. Compared to hard feces, soft feces were particularly enriched in solute marker concentration. Cecotrophy depends on a CSM that varies in its efficiency with the nutrient composition of the diet.

Digesta retention patterns in geese (Anser anser) and turkeys (Meleagris gallopavo) and deduced function of avian caeca

Although it is well-known that retrograde transport of urine fills the caeca of birds with fluid and small particles, the function of avian caeca is still not fully understood. We measured mean retention times (MRT) of solute (cobalt-EDTA, Co), small particle (<2mm, chromium-mordanted fibre, Cr) and large particle (8mm, cerium-marked fibre, Ce) markers in geese (Anser anser) and turkeys (Meleagris gallopavo) fed alfalfa pellets ad libitum. Intake did not differ between species. Turkeys had longer MRT for all markers (Co: 10.4 vs. 3.2h; Cr 23.3 vs. 2.9h; Ce 9.5 vs. 2.1h), achieved a higher fibre digestibility, and had a higher calculated dry matter gut fill. Thus, geese and turkeys correspond to the typical dichotomy of good fliers vs. poor fliers/flightless species in avian herbivores. Because uric acid is fermented much faster by microbes than fibre, the ultimate cause of short-MRT digesta retention in avian caeca as in geese is possibly rather uric acid than fibre fermentation. The numerical differences between marker MRT in geese correspond to a colonic separation mechanism that delays the excretion of fluids more than small and again more than large particles. In contrast to geese, turkeys excreted solid and liquid (caecal) faeces. Liquid faeces contained less fibre and more crude protein than solid faeces and accounted for the excretion of 7, 25 and 34% of Ce, Co and Cr markers. Marker excretion patterns and MRT for liquid faeces (Co 15 vs. Cr 50h) suggest that small particles did not simply move in parallel to fluids, but were retained selectively by being trapped in colonic digesta upon expulsion from caeca, with subsequent repeated retrograde transport into caeca with the next batch of urine. Given the absence of coprophagy in birds (in contrast to small mammalian herbivores), such a delay of small (microbial) particle escape from the caeca appears reasonable.

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.

Sheep of divergent genetic merit for wool growth do not differ in digesta kinetics while on restricted intakes

Sheep selected for high wool growth were previously shown to exhibit higher microbial protein outflow from the rumen and higher uptake of amino nitrogen in portal blood than those selected for low wool growth. This suggests that genetic selection for wool growth may induce changes in foregut physiology. This study was undertaken to determine whether differences in digesta kinetics, especially mean retention mime (MRT), are associated with differences in fleece production between sheep with low or high estimated breeding values (EBVs) for fleece weight. Twenty mature Merino wethers with uniform EBVs for liveweight were allocated to two groups of 10 animals on the basis of high or low EBVs for yearling fleece weight. Five sheep with low-EBVs and five sheep with high-EBVs for fleece weight groups were allocated in a crossover design to low and high feeding-level treatments, which comprised a blended hay diet fed at maintenance or 1.5 times maintenance. All sheep were given single doses of chromium-mordanted fibre and cobalt-EDTA as inert, non-digestible markers. Digesta kinetics was determined by analysis of the faecal marker excretion patterns using a compartmental model. Higher feed intakes from animals fed 1.5 times maintenance were associated with higher rates of wool growth and higher masses of indigestible fibre in the gut, but reduced MRT of digesta. Although sheep with higher EBVs for fleece weight had higher wool growth rates, there was no indication that these wool growth differences were associated with differences in digesta kinetics. The lack of interaction between feeding level and genotype suggests that MRT did not contribute to genotype differences in wool growth in sheep fed restricted intakes. The differences in wool growth among commercial Merino sheep with divergent fleece weight EBVs achieved by multi-trait selection are not attributable to differences in digesta kinetics, at least when feed is not available ad libitum.

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.

No ‘bypass’ in adult ruminants: Passage of fluid ingested vs. fluid inserted into the rumen in fistulated muskoxen ( Ovibos moschatus), reindeer ( Rangifer tarandus) and moose ( Alces alces)

In young ruminants, the reticular groove ensures that ingested milk is channelled past the forestomach to avoid malfermentation. It has been speculated that some adult wild ruminants, in particular browsing species, maintain a functional oesophageal (reticular) groove, that soluble nutrients can thus bypass the rumen, and that thus the energetic gain from the diet can be increased. We inserted a fluid marker (Co–EDTA) via cannula into the rumen and simultaneously fed a diet that contained a second fluid marker (Sm–EDTA), and analysed the faecal marker excretion patterns, in muskoxen ( Ovibos moschatus, n = 4 in two experiments each), reindeer ( Rangifer tarandus, n = 4 in a total of six experiments) and moose ( Alces alces, n = 1 in one experiment). In no case was the orally fed marker excreted distinctively earlier than the marker inserted into the rumen, which indicates that substantial bypass did not occur in these animals. However, differences between the three species in the excretion of the two markers from the rumen are consistent with hypothetical differences in the stratification of rumen contents. We suggest that effects previously ascribed to a “rumen bypass” in wild ruminants most likely reflect differences in the passage from the rumen.

Excretion patterns of titanium dioxide and chromic oxide in duodenal digesta and feces of ewes

Our objective was to examine differences in marker excretion patterns between Cr 2O 3 and TiO 2 in mature ewes fed diets varying in level of forage. Three experiments were conducted using an all forage diet, a 50% forage diet, and a 25% forage diet. In all three experiments, ewes were dosed intraruminally twice daily at feeding with gelatin boluses containing 2.5 g Cr 2O 3 and 2.5 g TiO 2. Following 7 days of adaptation to markers, fecal grab samples were collected at 6-h intervals for 6 days, representing every 1-h interval in a theoretical 24-h clock. On days 14–16 of each experiment, spot samples of duodenal digesta were collected at times representing 0, 2, 4, 6, 8, and 10 h after the morning feeding. Duodenal TiO 2 and Cr 2O 3 concentrations exhibited a diurnal pattern after feeding in all three experiments, but there were no marker × time interactions. Although fecal concentrations of TiO 2 were higher than Cr 2O 3 in all three experiments, there were no significant marker × time interactions observed. The lack of significant marker × time interactions resulted in little effect of sample collection frequency on mean concentrations of either marker, and as such, the frequency with which either duodenal or fecal samples are collected may be reduced in animals dosed twice daily without markedly affecting mean marker concentrations. Although estimates of digesta flow may differ between markers, the patterns of marker excretion observed suggest that TiO 2 behaves similarly to Cr 2O 3 within the gastrointestinal tract, and thus is an acceptable alternative to Cr 2O 3 for use in site and extent of digestion studies with ruminants.

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.

Retention time of feed particles and liquids in the stomachs and intestines of dairy cows. Direct measurement and calculations based on faecal collection

To validate a method for analysing indigestible marker excretion patterns in terms of digesta passage, the mean retention time (MRT) of long hay, ground hay and concentrate, marked, respectively, with thulium, ytterbium and dysprosium was measured in the total digestive tract (TMRT) and in the stomachs (SMRT) of four cows fed on a diet of hay in the long form (17.7 kg DM/day). The MRT of the particulate and liquid phases in the intestines was obtained after faecal particles labelled by Europium and Chromium EDTA were pulse dosed through the duodenal cannula. Following test meals, total faecal collection and spot sampling of duodenal digesta were performed at fixed intervals. TMRT were 51.7, 45.6, 40.6 h and SMRT were 39.5, 31.9 and 28.0 h, respectively, for hay, ground hay and concentrate. The MRT of the liquids in the rumen (8.7 h) was shorter than the SMRT of particles but there was no differential passage between liquids and particles after the duodenum. Intestinal MRT averaged 11 h and was partitioned into 7.5 and 3.5, respectively, for MRT in the tubular sections and the caecum-proximal colon. The compartmental analysis of the faecal patterns of markers given during a test meal gives the following results. The time associated with the descending part of faecal kinetics (respectively, 25.3 and 22.9 h for hay and concentrate) is directly related to the escape of feed particles from the rumen. The delay of first appearance of markers mostly reflects transit in the post duodenal tubular sections for the concentrate. The time associated with the ascending part (respectively, 16.9 and 9.4 h for hay and concentrate) represents the time required to reduce the size of the forage particles (7 h according to the difference between TMRT of long and ground hay direct measurements) and caecal mixing (3.5 h) as well as other compartments or processes that are not clearly identified.

Digestive Strategies of the Wombats: Feed Intake, Fiber Digestion, and Digesta Passage in Two Grazing Marsupials with Hindgut Fermentation

The wombats are grazing marsupials from mesic (Vombatus ursinus) and xeric (Lasiorhinus latifrons) regions of Australia. Feed intake and digestive responses of four wombats of each species were compared on two dietary fiber levels with pelleted straw-based diets of 59% and 44% neutral detergent fiber (NDF), and on two feed particle sizes with unpelleted and pelleted alfalfa hay. Dry matter (DM) intakes were similar between fiber levels but digestibilities of DM and NDF were greater on the low-fiber diet, with a trend to longer retention of digesta markers than on the high-fiber diet. Particulate (103Ruphenanthroline) and fluid (51CrEDTA) digesta markers were excreted in similar patterns, but mean retention times were longer for particles than for fluids (52-62 h vs. 30-36 h on the high-fiber diet). Marker excretion patterns and digestive tract anatomy were integrated into a model of digesta flow where axial flow of digesta was combined with irregular mixing along the haustrated proximal colon. Patterns of fecal particle size distribution and DM in-take of the alfalfa hays indicated a more thorough comminution of feed in the dental mill of Lasiorhinus than of Vombatus. The digestive strategies of the wombats feature enhanced digestive tract capacity (Vombatus) or length (Lasiorhinus) combined with low feed intakes, which result in long retention of digesta and yield fiber digestibilities similar to those of equids and macropod marsupials. These strategies enable wombats to utilize small home ranges with pastures of poor quality and/or low abundance.

On incorporating diffusion and viscosity concepts into compartmental models for analysing faecal marker excretion patterns in ruminants.

Deterministic mathematical equations are derived to describe the pattern of marker excretion in the faeces of ruminants under steady-state conditions when diffusion and viscosity concepts are introduced into a simple two-compartment scheme of the gastrointestinal tract. The basic scheme comprises a pure-mixing pool obeying first-order kinetics and a second compartment exhibiting streamline flow. Introduction of a velocity gradient, longitudinal diffusion or both into the second compartment, even with various simplifying assumptions, yields analytically insoluble equations. The impact of these mechanisms is to be investigated numerically rather than analytically in future work.

A multicompartmental model to describe marker excretion patterns in ruminant faeces.

A multicompartmental model, which assumes first-order kinetics, is proposed to describe digesta flow along the gastrointestinal tract of ruminants. Solution of the model yields a multiplicative equation, containing a single-exponential term and a double-exponential term, for describing faecal outflow rate. The logarithmic transformation of the equation was fitted to eighty-two excretion curves obtained after the administration of marker into the rumen of cattle and sheep, and compared with other published models. It was found to be superior to the other models in that it fitted all the data sets successfully.