Mean Retention Time Of Particles Research Articles

The effect of size and density on the mean retention time of particles in reindeer (Rangifer tarandus)

Particle passage from the reticulorumen (RR) depends on particle density and size. A classic way of assessing these effects is the use of plastic markers of varying density and size that are recovered in the faeces. Here, we report results of an experiment where four fistulated reindeer (Rangifer tarandus, 96 ± 12 kg) were fed two different diets (browse, voluntary dry matter intake [DMI] 70 ± 10 g/kg0.75/d; or a pelleted diet, DMI 124 ± 52 g/kg0.75/d) and dosed via fistula with 8 different particle types combining densities of 1.03, 1.22 and 1.44 g/ml and sizes of 1, 10 and 20 mm. Generally, particles that passed the digestive tract intact (not ruminated) did so relatively early after marker dosing, and therefore had shorter mean retention times (MRT) than ruminated particles. On the higher intake, the overall mean retention time (MRT) of particles was shorter, but this was not an effect of shorter MRT for either intact or ruminated particles, but due to a higher proportion of intact particles at the higher intake. This supports the concept that ruminants do not adjust chewing behaviour depending on intake, but that a lower proportion of digesta is submitted to rumination due to pressure-driven escape from the forestomach at higher gut fills. Compared to cattle (Bos primigenius taurus), muskoxen (Ovibos moschatus) and moose (Alces alces) that had received the same markers, reindeer had a lower proportion of 1 mm particles that passed intact. Our results support the concept that the critical size threshold for particles leaving the ruminant forestomach is dependent on body size. While the results likely do not represent findings peculiar for reindeer, they indicate fundamental mechanisms operating in the forestomach of ruminants.

A pilot investigation on the effect of induced saliva flow on digestive parameters in sheep, and a comparison with cattle.

Sheep with a relatively low methane yield were observed to have shorter fluid and particle mean retention times (MRT). Because the application of pilocarpine, a saliva stimulant, was successful in reducing retention times in ruminants in previous studies, we applied this substance to sheep, expecting a reduction in MRT and methane yield. Three non-pregnant sheep (74 ± 10 kg) were fed a hay-only diet in a 3 × 3 Latin square design with oral doses of 0, 2.5 and 5 mg pilocarpine/kg body weight and day. Measurements included feed and water intake, MRT of liquid and particulate phases in the reticulorumen (RR) and total gastrointestinal tract (GIT), ruminal microbial yield (via urinary purine bases and metabolic faecal nitrogen), total tract methane emission, apparent nutrient digestibility and rumen fluid parameters. Data were investigated for linear and quadratic effects using orthogonal polynomial contrasts. The MRT of liquid and small particles in the RR and total GIT, and the short-chain fatty acid concentration in rumen fluid, linearly declined with increasing pilocarpine dosage, while no quadratic relationship was detected. Intake of feed DM and water, apparent nutrient digestibility, methane yield and microbial yield were not affected by pilocarpine. When combining the sheep data with that of a similar experiment in cattle, we found that the MRT of the liquid phase was positively associated with estimated NDF digestibility and with methane production per digested NDF, but was not associated with microbial yield or the ratio of acetate to propionate. The ratio between MRT of the particulate and the liquid phase was smaller for sheep than that for cattle, and was not affected by treatment. Differences in this ratio might explain why species reacted differently to the saliva-inducing agent, which might help to explain the discrepancy between species in the effect of induced saliva flow on digestive parameters.

Is there a difference in ruminal fermentation control between cattle and sheep? A meta-analytical test of a hypothesis on differential particle and fluid retention

Ruminant species differ in digestive physiology. The species-specific ratio of mean retention time of particles and fluid (MRTparticle/MRTfluid) in the reticulorumen has been interpreted as controlling ruminal fermentation: a higher ratio indicates of a more distinct ‘washing’ of particulate digesta by liquid. This should increase the harvest of microbes from the reticulorumen, and keep the microbiome in a state of more intense growth; at the same time, this should increase the metabolic losses of faecal nitrogen of microbial origin, leading to lower values for the apparent digestibility of crude protein (aD CP). A systematic difference has been hypothesized between cattle (higher ratio) and sheep (lower ratio), with a lower MRTfluid in cattle due to a higher saliva production. Here, we test these hypotheses in a meta-analysis, using only studies that investigated cattle and sheep simultaneously. The datasets included 12 studies on MRT (of which 11 contained information on feed intake), yielding 102 (or 89) individual data; and 26 studies on protein digestibility (of which 18 contained information on intake), yielding 349 individual data. Cattle had a higher MRTparticle/MRTfluid (2.1) than sheep (1.7), mainly due to longer MRTparticle; only if body mass was included in the model, MRTfluid was significantly shorter in cattle in the larger MRT dataset (and tended to be shorter in the slightly smaller dataset). Cattle had a significantly lower aD CP than sheep, while there was no such difference in overall (dry or organic matter) digestibility. The dataset confirms a shift in fermentation strategy towards microbial production in cattle. While this has been suggested for ruminants in general, cattle appear particularly far on an evolutionary trajectory of maximizing microbial yield from the forestomach. The application of more specific digestive physiology data (like endogenous losses) gained from sheep to cattle should be done bearing these differences in mind.

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

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

Individual differences in digesta retention and their relation to chewing in cattle-A pilot investigation.

While information on individual differences in digesta mean retention time (MRT) might be interesting when selecting phenotypes for digestive efficiency, MRT measurements are prohibitively labour-intensive for large-scale application. Therefore, more easily measured proxies of MRT might be helpful. We used the opportunity of an experiment applying saliva stimulant in cattle to investigate the effect of different individual chewing behaviour on fluid and particle MRT with a consistent diet. Four non-lactating cattle (670-850 kg body mass [BM]) were used in a 4 × 4 Latin square design, treated with the saliva stimulant pilocarpine in dosages of 0, 1, 2.5and 5 mg/kg BM per day. The cattle were fed hay with dry matter intake (DMI) assigned according to their metabolic body weight. MRT in the whole gastrointestinal tract (GIT), the reticulorumen (RR) and the distal tract were measured using Co-EDTA, Cr-mordanted fibre and La-mordanted fibre as markers representing fluid, small particles (2 mm) and large particles (1 cm), respectively. The chewing behaviour was measured via noseband pressure sensor and expressed as chewing frequency (chews per time) and chewing intensity (chews per DMI), both for total chewing (ingestion plus rumination) and rumination chewing alone. The animals differed considerably in chewing behaviour and MRT measures. BM did not show a significant effect on chewing behaviour and MRT measures, though it tended to negatively correlated to total chewing intensity. Chewing intensity exerted a significant negative influence on MRT of fluid and particles in the RR, which was not the case for chewing frequency. Chewing frequency showed a significant relationship with MRT of large particles in the GIT. We suggest that chewing behaviour could influence MRT in two ways: (i) by affecting saliva production via the masticatory-salivary reflex and subsequently, the fluid inflow to the RR; (ii) by contributing to particle size reduction. Should the link between chewing behaviour and MRT be corroborated in larger studies, chewing measures, with their large interindividual variation, could emerge as an easy-to-measure proxy for MRT characteristics.

Body weight and sex effects on digesta mean retention time in growing Saanen goats.

Despite the important role of digesta mean retention time (MRT) on digestive efficiency of ruminants, it is poorly investigated in total gastrointestinal tract (GIT) of growing ruminants, especially in goats. The objective of this study was to evaluate the effect of body weight (BW) and sex on GIT MRT of particles and solutes in growing Saanen goats. A dataset from two studies, comprising 103 individual records of castrated males (n = 36), females (n = 34), and intact males (n = 33) Saanen goats slaughtered at 15, 22, 30, 37, and 45 kg BW, was used. Goats were fed basically with total mixed ration composed by dehydrated corn plant (Zea mays) milled to pass a 10-mm screen, cracked corn grain, and soybean (Glycine max) meal. Variables evaluated were BW, feed intake, feed intake level, composition of ingested diet, wet weight of GIT tissues, wet digesta pool size, digesta composition (dry matter and neutral detergent fiber [NDF]), indigestible NDF:NDF ratio of ingested diet and GIT digesta, MRT of particles (MRTiNDF) and solutes (MRTCr), and reticulorumen selectivity factors (large particles/solutes). Reticulorumen, omasum, abomasum, small intestine, cecum, and colon–rectum segments were evaluated. The dataset was analyzed as mixed models considering sex, BW, and sex × BW interaction as fixed effects, and study and residual error as random effects. Sex did not affect MRTiNDF in any GIT segments. Females and intact males presented similar reticulorumen MRTCr (5.6 h; P = 0.92) and they presented lower reticulorumen MRTCr than castrated males (7.0; P ≤ 0.04). Total GIT MRTCr was similar between castrated males and females (15.7 h; P = 0.11) and between females and intact males (14.2 h; P = 0.76). Body weight (BW) did not affect MRTiNDF in reticulorumen and colon–rectum and total GIT MRTCr (P ≥ 0.11). Reticulorumen and omasum MRTCr increased as BW increased (P < 0.01), and abomasum MRTCr decreased as BW increased (P = 0.02). Feed intake, and wet tissues and wet pool size of all GIT segments increased as BW increased, except abomasum wet pool size (P ≤ 0.01). The mechanism related to sex effect on MRT has to be elucidated. Reticulorumen MRTiNDF and total GIT MRTCr were modulated by intake and capacity of reticulorumen and GIT, respectively. On the other hand, reticulorumen MRTCr seemed to be regulated by reticulo-omasal orifice opening and saliva secretion.

Influence of particle size and density on mean retention time in the rumen of dairy cows

Increasing rumen-undegraded protein is one challenge of ruminant nutrition to both meet protein requirements of animals and reduce nitrogen excretion in the environment by increasing nitrogen efficiency. Industrial processes using heat or tanning to reduce rumen protein degradation have certain limitations, such as difficulty in balancing low ruminal degradation and high intestinal digestibility. Reducing the mean retention time (MRT) in the rumen by varying the size and density of particles may be another promising way to increase the rumen-undegraded protein proportion of concentrate feeds and improve the effectiveness of industrial processes. Spherical plastic particles of 3 mean diameter sizes (1, 2, and 3 mm) and 4 densities (0.9, 1.1, 1.3, and 1.5) were used to study the combined effect of size and density on the MRT of particles without interactions with microbial fermentations. Dynamics of fecal excretion of particles were monitored over 106 h (17 sampling times) in a Latin square experiment with 4 lactating cows. Cumulative particle excretion curves were fitted to a double exponential model to calculate total MRT in the digestive tract (TMRT), MRT in 2 compartments (MRT1 and MRT2), and retention time in the intestines' tubular section (TT). Differences in density had a quadratic effect, with densities of 1.1 and 1.3 yielding lower TMRT (29.5 and 31.2 h, respectively) than the densities of 0.9 and 1.5 (TMRT = 64.0 and 51.2 h, respectively). Similar responses were observed for MRT1, which was assumed to be the ruminal MRT for densities 1.1 and 1.3 (8.9 and 10.5 h, respectively) compared with densities 0.9 and 1.5 (39.6 and 22.6 h, respectively). Differences in diameter had a linear effect on TMRT (12.9 h longer for 3 mm than for 1 mm) and on TT. A combined effect of size and density was observed and particle size had no effect on TMRT when density was 1.1 to 1.3; however, outside this range, an increase in particle diameter increased TMRT. Consequently, a density of 1.2 to 1.3 is optimal for the escape of particles. As smaller particles of concentrates lose functional specific gravity more rapidly than larger particles due to their higher fermentation rate, our results, obtained with plastic particles, suggest that a diameter slightly greater than 3 mm seems a compromise to delay the start of fermentation and allow for rapid passage through the reticulo-omasal orifice.

Aspects of digestive function in sheep related to phenotypic variation in methane emissions

Ruminant livestock contribute to atmospheric methane (CH4) from enteric microbial fermentation of feed in the reticulo-rumen. Our research aimed to increase understanding of how digestive characteristics and rumen anatomy of the host animal contribute to variation in CH4 emissions between individual sheep. In total, 64 ewes were used in an incomplete block experiment with four experimental test periods (blocks). Ewes were chosen to represent the diversity of phenotypic variation in CH4 emissions: there were at least 10 offspring from each of four sires and a range of liveweights. Throughout the experiment, the ewes were fed equal parts of lucerne and oaten chaff, twice daily, at 1.5 times the maintenance requirements. Daily CH4 emission (g/day) increased significantly (P &amp;lt; 0.001) with an increasing dry-matter intake (DMI) and reticulo-rumen volume (P &amp;lt; 0.001). Lower methane yield (g CH4/kg DMI) was associated with shorter mean retention times of liquid (r = 0.59; P &amp;lt; 0.05) and particle (r = 0.63; P &amp;lt; 0.05) phases of the digesta in the rumen. Significant between sire variation was observed in CH4 emissions and in rumen volume (P = 0.02), the masses of liquids (P = 0.009) and particles (P &amp;lt; 0.03) in the rumen and the proportion of gas in the dorsal sac of the rumen (P = 0.008). The best predictors of variation in CH4 emissions due to the host were DMI, CO2 emissions, rumen volume, liveweight, mean retention time of particles in the rumen, dorsal papillae density and the proportion of liquid in the contents of the rumen compartments.

Influence of ruminal methane on digesta retention and digestive physiology in non-lactating dairy cattle.

Enteric methane (CH4) production is a side-effect of herbivore digestion, but it is unknown whether CH4 itself influences digestive physiology. We investigated the effect of adding CH4 to, or reducing it in, the reticulorumen (RR) in a 4×4 Latin square experiment with rumen-fistulated, non-lactating cows, with four treatments: (i) control, (ii) insufflation of CH4 (iCH4), (iii) N via rumen fistula, (iv) reduction of CH4 via administration of bromochloromethane (BCM). DM intake (DMI), apparent total tract digestibility, digesta mean retention times (MRT), rumen motility and chewing activity, spot breath CH4 emission (CH4exhal, litre/kg DMI) as well as CH4 dissolved in rumen fluid (CH4RRf, µg/ml) were measured. Data were analysed using mixed models, including treatment (or, alternatively, CH4exhal or CH4RRf) and DMI relative to body mass0·85 (rDMI) as covariates. rDMI was the lowest on the BCM treatment. CH4exhal was highest for iCH4 and lowest for BCM treatments, whereas only BCM affected (reduced) CH4RRf. After adjusting for rDMI, CH4RRf had a negative association with MRT in the gastrointestinal tract but not in the RR, and negative associations with fibre digestibility and measures of rumination activity. Adjusting for rDMI, CH4exhal had additionally a negative association with particle MRT in the RR and a positive association with rumen motility. Thus, higher rumen levels of CH4 (CH4exhal or CH4RRf) were associated with shorter MRT and increased motility. These findings are tentatively interpreted as a feedback mechanism in the ruminant digestive tract that aims at mitigating CH4 losses by shortening MRT at higher CH4.

Retention time of digesta in the gastrointestinal tract of growing Saanen goats.

This study examined the effect of increased BW on mean retention time (MRT) of both particulate and solute marker, gastrointestinal tract (GIT) development, and fiber digestion in the whole tract of growing Saanen goats using the slaughter technique. A total of 58 Saanen goats with initial BW of 15.7 ± 0.9 kg were allocated into 9 treatments with a 3 × 3 factorial arrangement consisting of 3 sexes (female, castrated males, and intact males) and 3 slaughter weights (initial, intermediate, and final; target BW of 16, 23, and 30 kg at slaughter, respectively). They were fed twice daily (0700 and 1600 h) with the identical diets for ad libitum intake. Mean retention time of particulate matter was estimated by in situ determination of indigestible NDF (iNDF), and the MRT of solute marker was determined by Cr-EDTA. Treatment effects were evaluated in a split-plot design, with sex as the main plot and slaughter weight as the subplot. Orthogonal polynomial contrasts were used to determine linear and quadratic effects of slaughter weight, whereas the effect of sex was compared using the Tukey test. The effects of sex and sex × slaughter weight were not significant for most of variables evaluated. The results showed that DMI (% BW) linearly decreased as slaughter weight increased ( < 0.01). Generally wet weight of the total GIT tissues (% BW) decreased and digesta pool sizes (g) linearly increased with increasing slaughter weight ( ≤ 0.05). The ratio of iNDF:NDF for both ingested diet and reticulorumen digesta linearly increased as slaughter weight increased ( ≤ 0.05). The MRT of particles did not change with increasing slaughter weight ( = 0.94). Mean retention time of particulate matter linearly increased in the omasum but linearly decreased in the abomasum with increasing slaughter weight ( < 0.01). Mean retention time of solute marker in the forestomachs linearly increased with increasing slaughter weight ( < 0.01). The results revealed a decreased selectivity with increasing BW, as supported by a greater ratio of iNDF:NDF for ingested diet. Increasing BW led to neither a longer particle MRT in the reticulorumen nor a digestive advantage. The results also indicated that, on average, 91% of fiber digestion occurred in the forestomachs of the goats.

Digestive physiology, metabolism and methane production ofcaptive Linné's two-toed sloths (Choloepus didactylus).

Sloths are renowned for their low metabolic rate, low food intake and low defecation frequency. We investigated factors of digestive physiology and energy metabolism in four captive individuals (mean body mass 10.0±SD 3.7kg) of a hitherto mostly unstudied sloth species, Linné's two-toed sloth (Choloepus didactylus), in a 2-week digestion recording and 23-h respiration experiment on animals fed a standard zoo diet of vegetables and starchy components. Dry matter intake, defecation frequency and particle mean retention time (MRT) in the gastrointestinal tract (GIT) were 12±3g/(kg(0.75) day), once every 5days and >140h in three individuals, but 53g/(kg(0.75) day), daily and 82h in one individual that was apparently compensating for a period of weight loss prior to the experiment. In all animals, solute marker was eliminated at a faster rate than the particle marker, indicating 'digesta washing' in the sloths' GIT. The overall metabolic rate calculated from oxygen consumption matched the metabolisable energy intake in three individuals [173±22 vs. 168±44 kJ/(kg(0.75) day)] but not in the fourth one [225 vs. 698 kJ/(kg(0.75) day)], supporting the interpretation that this animal was replenishing body stores. In spite of the low food intake and the low-fibre diet (209±26g neutral detergent fibre/kg dry matter), methane production was rather high accounting for 9.4±0.8% of gross energy intake (2.7% in the fourth individual), which exceeded literature data for ruminants on forage-only diets. These results corroborate literature reports on low intake, low defecation frequency, low metabolic rate and long MRT in other sloth species. The long MRT is probably responsible for the comparatively high methane production, providing more opportunity for methanogenic archaea than in other non-ruminant mammals to produce significant amounts of methane.

Simulation of Wood Particle Motion Through a Concurrent Triple-Pass Rotary Dryer

The retention time of solids in a drum is an important parameter for the design of rotary dryers, since it directly influences the mass and heat transfer rates. If it is too short, the wood particles do not become adequately dried. If it is too long, they become over-dried. Therefore, having an appropriate retention time is useful in terms of both energy and plant capacity. Wood particle mean retention time in a rotary dryer is affected by several variables, such as dryer dimensions, solid characteristics, and operational parameters. The purpose of this work was to simulate the effects of some wood particle characteristics and operational parameters on the mean retention time, drum holdup, and velocity of the wood particles during drying in a pilot-scale, closed-loop, triple-pass rotary dryer by means of a computer code. The simulation results of wood particle motion can be used for modeling, design, and optimization of closed-loop, triple-pass rotary dryers.

Intake, selection, digesta retention, digestion and gut fill of two coprophageous species, rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus), on a hay-only diet

A colonic separation mechanism (CSM) is the prerequisite for the digestive strategy of coprophagy. Two different CSM are known in small herbivores, the 'wash-back' CSM of lagomorphs and the 'mucous-trap' CSM of rodents. Differences between these groups in their digestive pattern when fed exclusively hay were investigated in six rabbits (Oryctolagus cuniculus) and six guinea pigs (Cavia porcellus). Intake, digestibility (by total faecal collection), solute and particle mean retention times (MRT, using Co-EDTA and Cr-mordanted fibres) were measured. Rabbits selected less fibrous parts of the hay than guinea pigs, leaving orts with higher content of neutral detergent fibre [NDF; 721 ± 21 vs. 642 ± 31 g/kg dry matter (DM) in guinea pigs]. They also expressed a lower NDF digestibility (0.44 ± 0.10 vs. 0.55 ± 0.05 of total), a similar particle MRT (15 ± 3 vs. 18 ± 6 h), a longer solute MRT (51 ± 9 vs. 16 ± 4 h), and a lower calculated dry matter gut fill (19.6 ± 4.7 vs. 29.7 ± 4.1 g DM/kg body mass) than guinea pigs (p < 0.05 for each variable). These results support the assumption that the 'wash-back' CSM, exhibited in the rabbits, is more efficient in extracting bacterial matter from the colonic digesta plug than the 'mucous-trap' CSM found in the guinea pigs. Related to metabolic body mass, rabbits therefore need a less capacious colon for their CSM where a more efficient bacteria wash-out is reflected in the lower fibre digestibility. A lighter digestive tract could contribute to a peculiarity of lagomorphs: their ability to run faster than other similar-sized mammals.

Retention of fluid and particles in captive tapirs ( Tapirus sp.)

The retention of ingesta in the digestive tract is a major characteristic of herbivorous animals. We measured particle and fluid mean retention times (MRT) in 13 lowland tapirs ( Tapirus terrestris) and 5 Malayan tapirs ( Tapirus indicus) from five zoological institutions on their usual zoo diet and 2 lowland and 4 Malayan tapirs additionally on roughage-only diets (total n of trials = 24) with cobalt-EDTA as fluid and chromium-mordanted fibre (< 2 mm) as particle markers. MRT for fluid and particles averaged 42 ± 16 h and 55 ± 18 h in lowland and 40 ± 13 h and 56 ± 14 h in Malayan tapirs. In a General Linear Model, neither Tapir species, body mass or diet (characterised by the proportion of roughage) was significantly related to MRT, but dry matter intake was, with a steep decline in MRT with higher intake levels. Compared to other hindgut fermenters, tapirs have a low defecation frequency, which might be linked to their comparatively low food intake. Their gastrointestinal capacity (in dry matter: 1.63 ± 0.63% of body mass) is similar to that calculated for horses. A comparison of the difference in fluid and particle MRT in large hindgut fermenters (horses, rhinoceroses, elephants, and the tapirs of this study) shows that longer absolute particle MRT are linked to shorter relative fluid MRT, possibly indicating a more thorough ‘washing’ of particulate ingesta with digestive fluids at longer particle MRT. The only outlier to this general pattern, with an exceptionally high difference between fluid and particle MRT, indicating a particularly efficient ingesta washing, is the white rhinoceros ( Ceratotherium simum). If possible, results of this study should be compared to findings in tapirs on natural diets.

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

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

Forage fibre digestion, rates of feed passage and gut fill in juvenile and adult red kangaroosMacropus rufusDesmarest: why body size matters

Using red kangaroos Macropus rufus Desmarest, a large (>20 kg) marsupial herbivore, we compared the digestive capabilities of juveniles with those of mature, non-lactating females on high-quality forage (chopped lucerne Medicago sativa hay) of 43+/-1% neutral-detergent fibre (NDF) and poorer quality, high-fibre forage (chopped oaten Avena sativa hay) of 64+/-1% NDF. On chopped lucerne apparent dry matter (DM) digestibilities by young-at-foot (YAF) red kangaroos (an age that would normally be taking some milk from their mother), weaned juveniles and mature females were similar (55-59%). On chopped oaten hay apparent DM digestibility was lower in the YAF (35.9+/-2.3%) followed by weaned (43.4+/-2.8%) and mature females (44.6+/-1%). The digestion of NDF and its components (mainly cellulose and hemicellulose) was lowest among the YAF followed by weaned and then mature females. The YAF and weaned kangaroos could not sustain growth on the poor-quality diet, and appeared to be at or near maximal gut fill on both forages; the values being 114-122 g DM for YAF and 151-159 g DM for weaned kangaroos. Mean retention times (MRT) of particle and solute markers were significantly longer for the YAF and weaned kangaroos on oaten hay than on lucerne hay, and DM intake (g d(-1)) was approximately 50% lower on the oaten hay. In contrast, solute and particle MRTs in the mature females were not significantly affected by diet; they maintained DM intakes by increasing DM gut fill from 264+/-24 g on chopped lucerne to 427+/-26 g DM on chopped oaten hay. Clearly, the mature female kangaroos did not maximise gut fill on the high-quality forage, presumably as a consequence of their proportionally lower energy requirements compared with still-growing juveniles. Overall, we have provided the first mechanistic link between the physiological constraints faced by juvenile red kangaroos in relation to their drought-related mortalities, rainfall and forage quality.

Fluid and particle retention times in the black rhinocerosDiceros bicornis, a large hindgut-fermenting browser

The mean retention time (MRT) of ingesta in the gastrointestinal tract is one of the major determinants of herbivore digestive physiology. We examined MRTs of fluids and particles in the gastrointestinal tract of six adult captive black rhinocerosesDiceros bicornis on conventional zoo diets. Fluid MRT ranged from 25–45 h and averaged 31 h. Particle MRT ranged from 28–59 h and averaged 38 h. In the six animals, both fluid and particle MRT declined as relative dry matter intake (g/kg metabolic body mass) increased. Black rhinoceroses, which are large hindgut-fermenting browsers, retained ingesta for a shorter period relative to their body size than grazing equids or grazing rhinoceros species. Our findings support the hypothesis that browsing hindgut fermenters have relatively shorter MRTs than grazing hindgut fermenters.

Impact of replacing starch by digestible fibre, at two levels of lignocellulose, on digestion, growth and digestive health of the rabbit

AbstractFour diets were arranged using a 2 ✕ 2 factorial design with two levels of lignocellulose, a high ‘HF’ or a low level ‘LF’ (acid-detergent fibre (ADF) = 191 v. 155 g/kg), combined with two levels of starch replacing 50 g/kg of digestible fibre (DF = hemicelluloses + pectins), a high starch (low DF) ‘HS’ or a low starch (high DF) level ‘LS’ (starch = 193 v. 123 g/kg). Two trials were conducted to measure digestive efficiency and rate of passage, respectively. A third trial was performed in a network of six French experimental breeding units to measure growth and digestive health on 507 rabbits per diet. Foods were offered ad libitum from weaning to slaughter.No significant interactions were detected between the effect of the level of lignocellulose and the effect of starch replacement by DF, on rabbit digestion, performance or digestive health. A proportional increase of overall food digestibility (organic matter (OM) or energy) was observed with the decrease of ADF level. When 50 g/kg of DF was replaced by starch we observed a significant improvement of OM and energy digestibility ( + 0·03 units). The whole-tract mean retention time of particles was 21 h. It was significantly longer with a lower ADF level ( + 5·4 h for LF v. HF diets), and it tended to increase when DF was substituted by starch ( + 2·2 h for HS v. LS diets).Between weaning and slaughter, food intake was mainly affected by the ADF level (139 v. 130 g/day respectively for HF and LF diets) and to a lesser extent by the replacement of DF by starch (136·2 v. 133·4 g/day, respectively for LS and HS diets). The weight gain was only slightly higher for high starch (low DF) diets ( +1 g/day) without an effect of the ADF level.Between weaning and slaughter, morbidity and mortality rates (from acute diarrhoea) were significantly reduced with high-fibre diets (-6 and -4 units respectively), while the replacement of DF by starch had no significant effect.

Site and extent of starch digestion of whole-plant maize silages differing in maturity stage and chop length, in dairy cows

The aims of this study were to determine the extent of starch digestion in the different digestive compartments in cows fed high whole-plant maize silage (WPMS) diets, and to evaluate the effect of maturity and chop length of WPMS on starch digestion, ruminal fermentation and milk production. The study was conducted on four dairy cows fitted with ruminal, duodenal, and ileal cannulas, in a 4×4 Latin square design. Dietary treatments differed in maturity stage (early vs. late) and chop length (fine vs. coarse) of WPMS. The WPMS were not processed. Diets, containing 80% WPMS, were fed at 90% of ad libitum intake level. Organic matter digestion in the different segments of the gastrointestinal tract and mean retention time of particles in the rumen and total tract, were similar between treatments. In late harvested WPMS, starch particle size distribution differed between coarse and fine chop length, and differences disappeared in rumen content. Total tract digestibility of starch was lower with late (95% of intake) than with early (99% of intake) stage. Starch ruminal digestion was high in comparison with diets containing similar proportion of starch provided by maize grain. Ruminal starch digestion was the highest with the early fine diet (95.4% of intake) and the lowest with the late coarse diet (71.3% of intake), and 70% of starch escaping ruminal digestion was digested in the small intestine. Starch digestion in hindgut was unaffected by treatments. The ruminal and total tract digestion of NDF and the ruminal pH, VFA, and ammonia concentrations were not or poorly affected by treatments. There was no difference in milk production and composition between treatments. Although differences in site of starch digestion between treatments were not statistically significant, this study suggested that the site and extent of starch digestion could be modulated by controlling maturity stage and chop length of WPMS, without affecting the energy value of the diet.

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.