Rumen Mean Retention Time Research Articles

The effect of dietary nitrate and canola oil alone or in combination on fermentation, digesta kinetics and methane emissions from cattle

Nitrate and lipids have been recognized as effective dietary additives to reduce enteric methane (CH4) production. The objective of this experiment was to evaluate the effects of nitrate (NO3¯) and canola oil, alone or in combination, on enteric CH4, volatile fatty acid (VFA) concentrations, digesta kinetics and outflow of DM and microbial non-ammonia nitrogen (MicNAN) from the rumen of cattle. Four rumen-cannulated steers were used in the experiment which was designed as 4 × 4 Latin Square with four 21-d periods and four treatments. Dietary treatments consisted of a control diet (CON: 400 g/kg lucerne chaff and 600 g/kg barley grain), NO3¯ (CON + 20 g NO3¯/kg), O (CON + 50 g canola oil/kg), and NO3¯+O (CON + 20 g NO3¯/kg + 50 g canola oil/kg) with all inclusions expressed as g/kg as-fed. Exogenous markers (Co-EDTA, Yb-acetate and 15NH4Cl) were continuously infused into the rumen over 4 d to estimate digesta flow and rumen N outflow while whole tract digestibility (DMD) was determined using chromic oxide. Compared with the CON diet, feeding the NO3¯+O diet reduced (P < 0.01) methane yield (MY, g CH4/kg DMI) by 25%, daily methane production (DMP, g CH4/d) by 26% (P < 0.01) and the rumen mean retention time (MRT; P < 0.05). Nitrate containing diets reduced DMD (P < 0.01). Total VFA did not differ between treatments (P > 0.05) but NO3¯-containing diets increased acetate proportion (P < 0.01) whereas feeding the O diet increased propionate proportion (P < 0.01). Oil-containing diets reduced rumen volume (P < 0.01). The rumen protozoa concentration was reduced by including NO3¯ and canola oil alone or in combination in the diet of cattle (P < 0.05). This experiment demonstrates that feeding NO3¯+O has a synergistic effect on reducing methanogenesis from beef cattle which is consistent with NO3¯ and canola oil having complementary mechanisms for suppressing enteric CH4 production. Reducing methanogenesis by feeding NO3¯+O in this experiment did not improve the flow of MicNAN from the rumen (g MicNAN/d), microbial growth efficiency (g MicNAN/digestible organic matter intake, DOMI) or the proportion of microbial N derived from rumen NH3.

The effects of fresh forages and feed intake level on digesta kinetics and enteric methane emissions from sheep

Published data have shown that in ruminants, methane (CH4) yields (g/kg dry matter [DM] intake) decline as feed intakes increase and, although the reduction has been attributed to a shorter digesta mean retention time (MRT), there are few supporting data. This study was undertaken to determine the association between digesta kinetics and CH4 emissions measured from sheep in respiration chambers fed either fresh white clover (Trifolium repens; WC) or fresh perennial ryegrass (Lolium perenne; RG) (Experiment 1), or RG at several feed intakes (Experiment 2). Measurements included CH4, whole tract apparent DM digestibility (DDM), total tract and rumen MRT (TMRT and RMRT, respectively) of solid and liquid fractions, as well as passage rates. In Experiment 1, eight sheep each with a rumen fistula were fed hourly either WC or RG forages, repeated over two periods (four sheep/diet/period) at about 1.6 times maintenance requirements for metabolisable energy (MEm; 1.12kg DM/d). Diet did not affect apparent DDM (726g/kg), CH4 yield (22.3g/kg DM intake), or TMRT of solid fractions (29.4h). However, TMRT for the liquid fraction was shorter (P=0.037) for sheep fed RG (17.4h) compared with WC (23.0h), and rumen digesta analyses suggested a larger rumen liquid pool size when RG was fed (6.05L) compared with WC (3.96L) (P=0.041). Experiment 2 involved 30 sheep offered fresh RG twice daily at about 0.8, 1.2, 1.6, 2.0 and 2.5×MEm. The DDM did not differ greatly across RG intakes (625–648g/kg) but, as RG intake increased (0.49–1.34kg DM/d), there were corresponding reductions (P<0.001) in CH4 yield (27.0–23.9g/kg DM intake), liquid TMRT (31.4–14.2h), solid TMRT (46.4–24.8h), liquid RMRT (18.4–7.5h), and solid RMRT (28.4–15.8h). When CH4 yield was plotted against rumen liquid and solid passage rates, the extent of the relationship was best explained (R2) when RG was fed at different intakes in Experiment 2 (0.71 and 0.66 for liquid and solids, respectively). The 2.7-fold increase in feed intake halved RMRT, but intakes affected passage of the rumen liquid fraction to a greater extent than solids. It can be concluded that reductions in CH4 yield from fresh forages fed to sheep are associated with shorter TMRT and RMRT. Understanding the effects of diet, digestion, feed intake, and feeding frequency on methanogenesis requires more knowledge about rumen digesta kinetics, especially relationships between outflow rates of solid and liquid fractions.

Rumen passage kinetics of forage- and concentrate-derived fiber in dairy cows

Rumen passage kinetics of forage and concentrate fiber were analyzed to determine intrinsic feed effects and extrinsic ration effects on the retention time of fiber in the rumen. Sixteen Danish Holstein cows (557±37kg of body weight, 120±21d in milk, mean ± SD), 8 fitted with ruminal cannulas, were used in a completely randomized block experiment. Treatments differed in forage type (corn silage vs. grass silage) and forage:concentrate ratio (50:50 vs. 75:25 on organic matter basis). Fiber passage kinetics were studied based on rumen evacuations and on marker excretion profiles in feces fitted to 1 and 2 pool models. Each cow received ytterbium (Yb)-labeled fiber of the forage fed in the ration, samarium (Sm)-labeled fiber of the forage not fed in the ration, and concentrate fiber labeled with lanthanum (La), all as a single pulse dose. Nineteen fecal grab samples were taken per cow. Rumen liquid passage was studied using chromium-EDTA dosed as a single pulse into the rumen, followed by sampling of rumen liquid from both the ventral and medial rumen. Rumen mean retention time did not differ between forages when based on Yb-excretion profiles but was numerically longer for grass silage– than for corn silage–based rations using rumen evacuation data. Liquid rate of passage did not differ when calculated from medial or ventral rumen liquid samples, indicating that estimates for the probability of rumen liquid escape were independent of rumen sampling site. Total mean retention time decreased from forage fiber to concentrate fiber to liquid. The forage type itself (corn silage or grass silage) rather than the ration composition seemed to determine the total-tract retention time of forage fiber.

Effect of feeding cows in early lactation with diets differing in roughage-neutral detergent fiber content on intake behavior, rumination, and milk production

This study measured the effects of including soyhulls as partial roughage replacement in total mixed rations (TMR) fed to 25 pairs of cows during early lactation, on the dry matter (DM) intake, particle kinetics, rumination, in vivo DM and NDF digestibility, milk and FCM yields, and BW changes. The 2 diets used in this study differed in the content of roughage and roughage NDF [23.5 vs. 35.0%, and 12.8 vs. 18.7% in the experimental (EXP) and control (CON) TMR, respectively]. The EXP TMR contained 20.5% less physically effective NDF than the CON TMR (11.7 vs. 14.1% of DM, respectively). These differences were expressed in a greater intake per meal (by 13.3%), a higher rate of meal intake (by 23.2%), a similar number of meals per day, a shorter daily eating duration (by 13%), and a higher total daily DMI (by 7.2%) in the EXP cows as compared with the CON cows. The in vivo DM and NDF digestibility was higher by 4.9 and 22.7%, respectively, in the EXP cows than in the CON cows. The rumination time for the TMR in the EXP cows was 12.7% (54.3 min/d) shorter than in the CON cows, and this was probably related to the difference of 12.4% in physically effective NDF intake between the 2 groups. Patterns of daily rumination and feed consumption throughout an average day showed a delay of approximately 1 to 2h between the eating and rumination peaks. Particle flow from the rumen of the EXP cows was characterized by a longer rumen mean retention time (by 17.8%) and longer rumination time per kilogram of roughage ingested (by 23.5%) as compared with the CON cows. Thus, favorable conditions for NDF digestion were created in the rumen of the EXP cows, as reflected in their rumen pH values (6.67). The advantage of the EXP cows in intake and digestibility was reflected in a concomitant increase of 7.4% in milk production and of 9.2% in FCM yield as compared with the CON cows. No difference was found between the 2 groups with respect to efficiency of feed utilization for milk production and BW changes.

Effect of diet composition on digestion and rumen fermentation parameters in sheep and cashmere goats

The study was carried out to compare the voluntary intake, digestibility, mean retention times (MRTs) and rumen fermentation parameters in sheep and cashmere goats offered three pellet diets. Four Mongolian and Han crossbred sheep and four Inner Mongolian white cashmere goats, each fitted with a rumen cannula, were used in this study. The results showed that there were differences between sheep and goats in voluntary intake (P<0.05), apparent digestibility of fiber and MRT (P<0.01). Dietary types affected voluntary intake, apparent digestibility and rumen fermentation parameters (except pH). Sheep showed high voluntary dry matter (DM) intake, long rumen MRT and high apparent digestibility of fiber. When opportunity for diet selectivity was avoided, cashmere goats, compared with sheep, showed lower voluntary DM intake, shorter rumen MRT and lower apparent digestibility of fiber. Rumen fermentation parameters did not show differences between sheep and goats.

Suitability of synthetic alkanes as markers for the estimation of passage rate in sheep

An experiment was conducted with eight adult wethers housed individually in metabolism crates to determine the suitability of alkanes to serve as passage rate markers in sheep. Two diets consisting of lucerne (800 g DM/d), without (treatment ‘Lucerne’) and with coarse maize meal (270 g DM/d; treatment ‘Lucerne–Maize’) were fed to four sheep per diet twice daily in equal proportions. Lucerne fibre was prepared from chopped lucerne silage and mordanted with chromium during 24 h cooking with sodium–lauryl–sulfate (Chromium–mordanted lucerne fibre: LF- Cr). The synthetic alkane C36 was dissolved in heptane and sprayed onto lucerne fibre which had been similarly prepared (LF- C36). C28 was dissolved in heptane and sprayed onto maize meal (M- C28). Markers were fed at the same time as a pulse dose. For a period of 10 days, rectal grab faeces samples were taken in intervals of increasing length (2–12 h). A multi-compartment-model was fitted to the marker excretion curves. Maximum marker excretion appeared earlier for alkane markers than for Cr in both treatments. Within treatment Lucerne no significant differences between Cr and C36 were detected for Rumen mean retention time (MRT) ( P > 0.05). Numerical differences were observed for RumenMRT in treatment Lucerne–Maize between LF- Cr and LF- C36 and M- C28 (33, 25 and 25 h), respectively. Further numerical differences were observed in CaecumMRT for LF- Cr and LF- C36 in treatment Lucerne and for all markers in Lucerne–Maize. In treatment Lucerne, faecal recoveries of markers LF- Cr and LF- C36 were 95 and 85%, in treatment Lucerne–Maize 101 and 88%, and for M- C28 in the treatment Lucerne-Maize only 75%. It was shown that the lower faecal recovery of alkanes by itself does not cause biased estimates of passage rate parameters. However, further investigations are necessary to determine the relationship between the time a particle has spent in the digestive tract and the disappearance of the alkane marker, as this could introduce a bias to the estimate. The major shortcoming of alkanes as passage rate markers seemed to be migration between solid and liquid phases of the digesta. This problem could be overcome by new labelling procedures or the use of 13C-labelled native alkanes.

Feed intake, digestion kinetics and rumen volatile fatty acids in Menz rams supplemented with Lablab purpureus or graded levels of Leucaena pallida 14203 and Sesbania sesban 1198

35 Menz rams weighing 19.3 ± 0.87 kg (mean ± S.D.) were used in a randomized block design experiment that was conducted for 35 days at Debre Zeit Research Station of the International Livestock Research Institute, Ethiopia. The objectives of the study were to determine feed intake, apparent digestibility, passage rate and level of rumen volatile fatty acids (VFA) in Menz rams fed tef ( Eragrostis tef) straw. The basal diet was supplemented daily on DM basis with dried foliage of Lablab purpureus, LAB – (230 g) or graded levels of Leucaena pallida 14203, namely, LP1 – (170 g), LP2 – (230 g), LP3 – (290 g), and Sesbania sesban 1198, namely, SS1 – (170 g), SS2 – (230 g), and SS3 – (290 g). The nitrogen (N) content of the supplement feeds was over 28.8 g kg −1 DM, whereas it was only 8.5 g kg −1 DM in the basal feed. High contents of NDF (747.6 g kg −1 DM) and ADF (419.5 g kg −1 DM) were determined in tef straw compared to the supplement feeds. Among the supplement feeds, L. purpureus had relatively high NDF (454 g kg −1 DM) and ADF (346.2 g kg −1 DM) content. L. pallida 14203 contained relatively high levels of the anti-nutritive factors, namely, condensed tannins (82.7 Abs g −1 NDF) and soluble phenolics (27.9 g kg −1 DM). Basal feed DM intake ( P < 0.05) reduced with an increase in the level of L. pallida 14203 supplementation. The apparent digestibility of N, ADF and ADL was lower ( P < 0.001) in L. pallida 14203 than in L. purpureus or S. sesban 1198 supplemented rams. L. pallida 14203 promoted lower ( P < 0.05) fractional outflow rate of particulate matter from the rumen and longer rumen mean retention time than L. purpureus and S. sesban 1198. Higher levels of total VFA ( P < 0.001) were observed in S. sesban 1198 than in L. pallida 14203 supplemented rams. It was concluded that the anti-nutritive factors in L. pallida 14203 have a major impact on fractional outflow rate of particulate matter from the rumen, and the digestibility of nutrients, with particular limitations on N digestibility. Increasing levels of S. sesban 1198 supplementation reduced nutrient digestibility due to increased passage rate, and thus supplementation of animals with the lowest level of the fodder tree appears to be more appropriate. The relatively high fiber content of L. purpureus reduced intake and apparent digestibility of feed on a limited scale.

Effect of physical form of a lucerne hay on rumination and the passage of particles from the rumen of sheep

Six 2-year-old Corriedale wethers fitted with rumen and abomasal cannulas were given a lucerne hay, first as chopped (CH) hay then as ground and pelleted (GP) hay. Intake rate increased as dry matter intake (DMI) increased and was greater on GP hay. The time spent eating and ruminating per unit of DMI decreased as DMI increased and was shorter on GP. Ruminating efficiency increased with DMI but did not differ between CH hay and GP hay. The critical size of particles for passage from the rumen was not affected by either DMI or by grinding and pelleting. Most of the overall digestion of large particles (LP) occurred during their retention in the LP pool within the rumen, and retention in the medium particle (MP) pool accounted for much of the rumen mean retention time of particles. The residual digestible material of MP derived from LP by rumination appeared to be less accessible to fermentative activity. Prediction of an animal’s response to the grinding and pelleting of forage must take account of all the determining factors and their interactions.

The effect of physical form of orchardgrass hay on the passage of particulate matter through the rumen of sheep.

Four Texel wethers (60 to 64 kg) fitted with ruminal and duodenal cannulas were used to study the kinetics of particulate matter in the rumen and the series of processes involved in their selection and passage. They were fed, in eight equal meals, 1,200 g of a mixture of a chopped orchardgrass hay and ground (8-mm screen) and pelleted orchardgrass hay in 90/10, 50/50, 30/70, or 10/90 ratios, according to a 4 x 4 Latin square design. The particle size distributions in feed, chewed feed, and ruminal, reticular, and duodenal digesta were determined by a wet-sieving procedure. Indigestible lignin was used as an internal marker to trace the passage of particles through the rumen. Digesta flow measurement was performed using the double-marker technique. We used a three-pool model, which partitions particles through the large, medium, and small particle pools, to determine the passage of lignin through those pools. Particle pool sizes and rumen and pool mean retention times (MRT) of lignin and of the rumen MRT of an ideal marker introduced separately in each pool were corrected for the "filter bed" effect. Grinding and pelleting of hay decreased the MRT of the indigestible lignin pool in the rumen. Particle MRT decreased and then reached a plateau with increased proportion of ground/pelleted hay in the diet. The diet with a ratio of 50/50 of chopped and ground/pelleted hay was the most favorable for the exit of particles from the rumen because of both a higher outflow rate from the rumen of particles eligible to exit and a sufficient comminution rate of larger particles to supply particles that were able to pass. For all diets, the large-particle comminution rate was always higher than the small-particle outflow rate, indicating that comminution was not the limiting step for passage. These results were the consequence of the curvilinear and opposite evolutions of both the particulate lignin pool in, and outflow from, the rumen. Those results contribute to an improved explanation of the mechanisms involved in the outflow of particles from the rumen.

Rumen characteristics, methane emissions, and digestion in weaned lambs reared in isolation

Twelve Merino lambs were separated from their dams at 2 days of age. Six were reared in isolation and 6 were inoculated with rumen fluid when 4 weeks old. Apelleted, mixed diet was available from 10 days of age; milk feeding was restricted to maintenance from 2 weeks and discontinued when liveweight reached 9 kg. Three lambs from each group were given a medium intake and 3 a high intake of the diet. The isolated lambs had virtually no rumen protozoa; rumen ammonia and volatile fatty acid concentrations were lower in these lambs but acetate:propionate ratios were higher. The rumen mean retention time (MRT) of a solute marker was longer but the microbial turnover time (TT) was shorter in the isolated lambs; both MRT and microbial TT were shorter on the high intake. Total microbial synthesis did not differ between groups. The digestibilities of energy, organic matter, non-structural carbohydrate, and crude protein were lower in the isolated lambs but those of cell wall constituents were not affected significantly; digestibilities were lower on the high intake. The isolated lambs emitted much less methane than the inoculated lambs; consequently, available energy (i.e. digestible less methane energy), was similar for the 2 groups. Recovery of reducing equivalents in the rumen fermentation was incomplete in the isolated lambs but could be accounted for if reductive acetogenesis provided 13% (medium intake) or 16% (high intake) of the acetate and butyrate formed.

Effect of forage to concentrate ratio on comparative digestion in sheep, goats and fallow deer

AbstractThree ewes, three female goats and three male fallow deer, aged between 7 and 12 months and weighing 24·0 to 32·2 kg, were used in this experiment to outline the main differences in digestion among the three species. Dietary treatments were three diets with three forage: concentrate ratios of 10: 90, 50: 50, and 90:10 and two different feeding levels (45 and 90 g/kg M0·75per day). The three diets were given to the three animals of each species in a Latin-square design; the two levels of feeding were compared ivithin diet in each period of the Latin square. The diet selected, apparent digestibility, and rumen retention time of Cr-mordanted neutral-detergent fibre were significantly different among species and dietary treatments. Interactions between species and dietary treatments were also significant for all the above variables. Sheep showed the highest intakes and apparent digestibilities of the forage-rich diets, and the longest rumen mean retention times. Goats tended to select diet components, despite allowance of diets being limited, and had lower food intakes than sheep. Apparent digestibility of forage-rich diet was also lower. Rumen mean retention times were shorter and less influenced by dietary treatments. Fallow deer had an apparent digestibility of forage-rich diets which was even lower than that of goats. Food intake was similar to that of sheep, with no evidence of selection. Rumen mean retention time was shorter than that of goats.

Digestion and chewing behaviour of young sambar and red deer consuming a low quality roughage

SUMMARYLow quality chaffed meadow hay, containing 10·5 g N/kg dry matter (DM), was fed to four artificially reared sambar (tropical) deer (Cervus unicolor) and four red (temperate) deer (Cervus elaphus) confined indoors in metabolism crates at Palmerston North, New Zealand, during March and April 1994. Measurements were made of DM intake (DMI), apparent digestibility, nitrogen (N) retention and the time spent eating and ruminating. Voluntary food intake (VFI), measured over days 7–11, was substantially greater for red deer than for sambar deer (67 v. 36 gDM/kgW0·75/day). Dry matter intake of red deer was then restricted, so that apparent digestibility could be better compared between the two species. Eating and ruminating time/gDMI and chews during eating/gDMI were all greater for sambar deer than for red deer. Apparent digestibility of DM, organic matter (OM) and energy were low (c. 0·42) and not different between deer species. Apparent digestibility of neutral detergent fibre (NDF) and cellulose were highest for red deer, but lignin apparent digestibility was highest for sambar deer. Both deer species lost weight and were in negative N balance. However, despite their lower N intake, sambar deer lost significantly less N and liveweight per day (– 5·6 g and – 118 g) than red deer (– 12·2 g and – 258 g). It was concluded that red deer responded to a diet of low quality roughage by increasing VFI and cellulose digestion, whilst sambar deer responded with a lower VFI but greater chewing activity, improved lignin digestion and better N conservation. Rumen mean retention time should be measured in future experiments with sambar deer and red deer fed on low quality forage diets.

Effect of draught work on performance and metabolism of crossbred cows 2. Effect of work on roughage intake, digestion, digesta kinetics and plasma metabolites

AbstractForty pregnant F1crossbred dairy cows (20 Friesian × Boran and 20 Simmental × Boran) were stratified in a 2 × 2 diet × work factorial arrangement (not working-not supplemented, NWNS; not working-supplemented, NWS; working-not supplemented, WNS; and working-supplemented, WS) were used to study the effect of work and diet supplementation on roughage intake, apparent digestibility of nutrients, digesta kinetics and plasma metabolites. Dry matter (DM) and organic matter (OM) intakes were greater for working than for non-working cows. Work and supplementation increased DM and OM in vivo apparent digestibility. This effect was particularly significant when comparing working cows at rest and at work. Passage rate and rumen mean retention of Cr-mordanted hay were similar for working and for nonworking cows. Liquid turn-over rate of Co-ethylene diamine tetra acetic acid (EDTA) was lower and rumen mean retention time of Co-EDTA was greater in working than in non-working cows whether supplemented or not. Working coios had lower plasma glucose during and immediately after working than non-working cows. Plasma non-esterified fatty acid (NEFA) was higher in working cows at the end of the working period and after rest between working hours. This effect was greater in non-supplemented than in supplemented cows. In working cows, β-hydroxybutyrate was lower at the end of working hours than in non-working cows. Lactate was greater in working than in non-working cows after the 3rd and 4th hours of work. Digesta kinetics could explain only partially the possible mechanisms responsible for greater roughage intake and apparent digestibility in working cows. The decrease of plasma glucose and the increase in NEFA during work indicates an increasing utilization of NEFA by muscle during consecutive working hours.

Rate of passage of digesta during and after weaning in calves fed concentrate diets containing pea or soya-bean meal

The transit of hay, concentrate and water was studied in various parts of the digestive tract of dairy calves progressively weaned on high-concentrate diets differing in the source of protein (pea vs. soya-bean meal). The mean retention time (MRT) of the ration constituents in the whole tract and the stomachs of calves was almost unaffected by weaning. Compartmental analysis of faecal marker kinetics however revealed a decrease in hay and concentrate transit time in the tubular parts of the gut after weaning. The nature of the dietary proteins tested had only small effects on passage-rate parameters. Despite dramatic changes in the nature of the feeds and level of intake, weaning seems to be characterized by a fairly constant rate of passage of solids and liquids throughout the gut of the young dairy calf. The reliability of estimating the MRT within the rumen from the analysis of faecal marker kinetics was assessed by duodenal sampling; correlations between faecal and duodenal estimates of the rumen MRT were low in the present experiment.

Relationships between organic-matter digestibility, dry-matter intake and solute mean retention times in sheep given a ground and pelleted diet

SUMMARYThe relationships between organic-matter digestibility (OMD), dry-matter intake (DMI) and the mean retention time (MRT) of unabsorbed solutes in the gastrointestinal tract were examined using six fistulated, cross-bred, castrate male sheep. Measurements were made on each sheep at two different DMIs within the range 28–81 g D.m./(day. kg0·75). There were negative, curvilinear relationships between MRTs (both rumen and total) and DMI and positive, curvilinear relationships between OMD and MRTs. As a consequence, there was a negative, rectilinear relationship between OMD and DMI. OMD declined by 0·022 when DMI increased from calculated maintenance to twice maintenance. The proportion of the total MRT accounted for by rumen MRT did not change significantly; the mean value was 0·364 ( ± S.e. 0·010).

Interpretation of the faecal excretion patterns of solute and particle markers introduced into the rumen of sheep

SUMMARYA two-pool + time delay model was used to analyse ideal marker concentration patterns generated, using an interactive computer simulation program, from data for the mean retention times of [51Cr]EDTA and [103Ru]phen in the reticulo-rumen, abomasum and caecum-proximal colon and the transit times of these markers through the omasum, small intestine and distal large intestine of sheep. Although providing a reasonably close fit to the generated data, the fitted curves showed small but systematic deviations, indicating that the model does not consistently characterize the kinetics of the markers in the ruminant gastro-intestinal tract.When the components of the two-pool model were correctly identified, predicted rumen mean retention times (MRT) were within – 1 to + 13% of the observed values. However, identifying the component with the longer MRT as the rumen resulted in up to 2·6-fold overestimation (17·5 v. 6·77 h). The model underestimated the time delay and the overall MRT. It is suggested that the correct identification of the two components can be achieved by the simultaneous use of a solute-and a particulate-phase marker because, in ruminants, they do not behave independently in the caecumproximal colon.

Digestion of a ground and pelleted diet in the stomach and intestines of young sheep from two breeds

Some aspects of digestion were studied in small groups of fistulated wether lambs from two breeds, Dorset Horn and Corriedale. The Iambs were given a ground and pelleted diet of equal parts hay and concentrates once daily at two levels of intake. At the same liveweight (25 kg), the higher intake was associated with reduced digestion of organic matter (OM) and fibre in the whole gastro-intestinal tract; rumen mean retention times were also reduced, as was the proportion of OM digestion which occurred in the rumen. An increase in the amount of protein entering the intestines appeared to be composed of both undegraded dietary protein and microbial protein. Despite a reduction in the digestibility of non-ammonia nitrogen in the intestines, more crude protein was digested there per unit of digestible OM intake (25.9 v..23.6%; P &lt; 0.05). Differences between the breed groups were smaller than those associated with level of feeding. Nevertheless, particularly at lower relative intakes, rumen mean retention times were longer, rumen digesta content was greater, and rumen OM and fibre digestion tended to be greater in the Dorset Horn lambs; crude protein digestion in the intestines per unit of digestible OM intake also tended to be less at the low intakes. More than three-quarters of the cellulose digestion but less than half the hemicellulose digestion occurred in the rumen. The proportion of the urea synthesized that was degraded in the gastrointestinal tract (0.24-0.30) was consistently lower in these lambs than has been reported for adult sheep.