Digesta Passage Research Articles

Effects of Food Intake on Digesta Passage Time in Captive Japanese Martens (Martes melampus) and Implications for Endozoochorous Seed Dispersal

Abstract. To examine the effects of food intake on the gastrointestinal passage time of seeds in the Japanese marten (Martes melampus), we conducted four feeding experiments using captive animals (n = 4). We estimated passage time variables (transit time and mean retention time) of plant seeds (two types) using two different numbers of chicks (single and three) representing two seasons when the animal prey is abundant/scarce. There was no significant relationship between food intake and passage time, and seed type did not affect the passage time variables. Our results were different to those for herbaceous/omnivorous mammals, in which a shorter passage time was observed when food intake increased. The stability in the passage time of the martens could be attributed to the higher level of digestibility of the animal prey. Our data also suggests that martens possess an elastic gut that can expand in volume, which leads to a consistent passage time despite the increase in food intake and enables them to effi...

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Intake and performance of goats fed exclusively forages Tifton 85, mulberry or leucaena were simulated to verify which nutrients limit performance. Simulations were performed using the nutritional model similar to Cornell Net Carbohydrate and Protein System (CNCPS) with modifications related to the kinetic attributes of digestion and feed passage. The animal category chosen to perform the simulations was female Saanen goats in growing phase between weaning and mating, with 20 kg of body weight and 150 g of daily gain. The intake of 0.870 kg/day of Tifton 85 was adopted for performance simulations because in this point caused rumen fill and also attended the energy requirement of the animal. For performance simulations of mulberry, the amount of dry matter intake of 0.580 kg/day was adopted based on average intake obtained from the study of Sabino Jr. (1996) and simulations for leucaena used the intake of 0.220 kg/day, corresponding to 30g/100g of dry matter intake that would supply the energy requirement of these female goats. The limiting factor of performance of Saanen female growing goats fed exclusively Tifton 85 or mulberry is the metabolizable protein and not the energy. The intake of leucaena exclusively would be able to supply the requirement of metabolizable protein to promote the target weight gain of 150 g/day. The forages do not present perfect synchronization between carbohydrates and proteins, demonstrated by the positive ammoniacal balance in rumen environment that indicates an excess of nitrogen compounds supplied by these feed.

Binturong (Arctictis binturong) and Kinkajou (Potos flavus) digestive strategy: implications for interpreting frugivory in Carnivora and primates.

Exclusive frugivory is rare. As a food resource, fruit is temporally and spatially patchy, low in protein, and variable in terms of energy yield from different carbohydrate types. Here, we evaluate the digestive physiology of two frugivorous Carnivora species (Potos flavus, Arctictis binturong) that converge with primates in a diversity of ecological and anatomical traits related to fruit consumption. We conducted feeding trials to determine mean digestive retention times (MRT) on captive animals at the Carnivore Preservation Trust (now Carolina Tiger Rescue), Pittsboro, NC. Fecal samples were collected on study subjects for in vitro analysis to determine methane, pH, and short chain fatty acid profiles; fiber was assayed using standard neutral detergent (NDF) and acid detergent (ADF) fiber methods. Results indicate that both carnivoran species have rapid digestive passage for mammals that consume a predominantly plant-based diet: A. binturong MRT = 6.5 hrs (0.3); P. flavus MRT = 2.5 hrs (1.6). In vitro experiments revealed no fermentation of structural polysaccharides – methane levels did not shift from 0 h to either 24 or 48 hours and no short chain fatty acids were detected. In both species, however, pH declined from one incubation period to another suggesting acidification and bacterial activity of microbes using soluble carbohydrates. A comparison with primates indicates that the study species are most similar in digestive retention times to Ateles – the most frugivorous anthropoid primate taxon.

Effects of gestation and lactation on forage intake, digestion, and passage rates of primiparous beef heifers and multiparous beef cows1

Angus-cross cows (n = 13; 8 pregnant, BW 610 ± 24 kg, and 5 nonpregnant, BW 571 ± 23 kg) and heifers (n = 13; 8 pregnant, BW 511 ± 40 kg, and 5 nonpregnant, BW 451 ± 60 kg) were individually fed chopped warm-season grass hay (5.5% CP, 67% NDF) for ad libitum intake and soybean meal (46% CP) at 450 g/d. Intake was measured daily, and DM digestibility, digesta passage rate, and plasma glucose and β-hydroxybutyrate (BHBA) concentrations were measured every 14 d from 49 d prepartum to 49 d postpartum. Prepartum DMI (% of BW) increased over time for pregnant heifers through 2 wk prepartum before declining but did not change over time for pregnant cows. Dry matter digestibility decreased with advancing gestation (P < 0.001); pregnant animals had greater digestibility than nonpregnant cows and heifers (P = 0.02). Digestibility was not influenced by age (P = 0.99). Pregnant cows and heifers had faster digesta passage rates than their nonpregnant counterparts (P = 0.02). Pregnant animals had lower plasma glucose (P < 0.001). Plasma BHBA concentrations were greater in pregnant animals than in nonpregnant animals (P < 0.001) but were not influenced by age (P = 0.27) or time prepartum (P = 0.98). Postpartum DMI (% of BW) was greater for lactating heifers than other groups (age × lactation status; P = 0.05) and increased over time (P < 0.001). Diet digestibility increased with time postpartum (P < 0.001), and heifers had greater digestibility than cows from 3 to 7 wk postpartum but not at 1 wk postpartum (age × time; P = 0.02). Postpartum passage rate was not influenced by age or lactation status (P > 0.23). Lactating animals had lower plasma glucose and greater plasma BHBA concentrations postpartum than nonlactating animals (P < 0.001). Calves from mature cows grew faster than calves from heifers (age × time; P < 0.001). These data show that although primiparous beef heifers have similar DM digestibility, passage rates, and plasma glucose and BHBA concentrations, intake patterns differ between heifers and cows. Although DMI (% of BW) and digestibility did not differ between pregnant beef heifers and pregnant mature cows, the DMI (% of BW) was greater for lactating primiparous cows (heifers) than for lactating multiparous cows. Even with their postpartum increase in DMI, primiparous beef heifers were not able to consume adequate amounts of the warm-season forage to support their requirements for maintenance, growth, and lactation.

Short communication: Comparison of 3 solid digesta passage markers in dairy cows

This study investigated the usefulness of acid-detergent fiber-bound 15N [acid detergent insoluble (ADI)-15N] as a solid digesta passage marker in dairy cows compared with chromium (Cr) and ytterbium (Yb) (as labeled fiber or forage, respectively). Intrinsically (ADI-15N) or extrinsically (Cr, Yb) labeled alfalfa hay was pulse-dosed intraruminally to 7 lactating dairy cows. Following marker administration, spot fecal samples were collected for up to 72h for marker analyses. Urine and milk samples were also collected and analyzed for Yb and Cr. Fecal marker excretion data were processed using 2-compartment mathematical age-dependent/age-independent (Gn→G1) models. The rate of passage of the marker in the first, age-dependent compartment tended to be slower for Yb compared with Cr and ADI-15N, which resulted in a trend for longer mean retention time (MRT) in this compartment when Yb was used as a marker (19.0h) compared with Cr and ADI-15N (14.5 and 13.9h, respectively). The rate constant of marker disappearance for the second or age-independent compartment tended to be greater for Yb compared with Cr and ADI-15N, which led to a shorter MRT of Yb in this compartment (15.6) versus ADI-15N (32.1) and Cr (24.8h). The cumulative MRT was greater for ADI-15N versus Cr and Yb (46.0, 39.3, and 34.4h, respectively). Total MRT of marker tended to be greater for ADI-15N than for Yb (46.6 vs. 36.6h, respectively). Urine and milk analyses data suggested no measurable losses of Yb along the digestive tract, but about 0.79% of Cr dosed intraruminally was secreted or excreted in milk and urine in the 48-h period following marker administration. Collectively, this study confirmed previous observations that ADI-15N can be used reliably as a solid digesta passage marker for ruminants, producing pre-duodenal and total-tract retention times similar to that of Cr-labeled fiber. Retention time in the age-independent compartment was underestimated when Yb was used as a marker, emphasizing the need to process forages to isolate fiber before labeling with Yb.

Palm Kernel Cake as a Potential Ingredient in Muscovy Ducks Diet

A study was conducted to determine the feeding effect of three concentration levels of 0, 15 and 35% palm kernel cake (PKC) on productive performance of Muscovy ducks during growing period. A total of 72 males and 72 females two week-old ducklings were randomly assigned to one of three experimental diets: corn-soybean meal basal diet (control); basal diet containing 15% PKC (PKC15); and basal diet containing 35% PKC (PKC35). Following five weeks of growing phase with experimental diet, no significant differences were observed in respect to body weight and weight gain among treatments. However, feed intake and feed to gain ratio was significantly higher in birds fed 35% PKC than those in other treatment groups. Male ducks had significantly superior weight gain and feed to gain ratio. This was mainly due to their higher feed intake level and not attributed to nutrient digestibility coefficients. Inclusion of 35% PKC decreased (P<0.05) the dry matter, energy and crude protein digestibility compared to 15% and control group. This reduction was mainly influenced by the shorter digesta passage time in 35% PKC fed birds (P<0.05). There were no significant differences between the control and 15% PKC birds as for all the investigated parameters. Therefore, it is suggested that PKC may be incorporated in Muscovy duck diet at 15% without any adverse effect on the overall performance and nutrients digestibility.

Stable isotope‐labelled feed nutrients to assess nutrient‐specific feed passage kinetics in ruminants

Knowledge of digesta passage kinetics in ruminants is essential to predict nutrient supply to the animal in relation to optimal animal performance, environmental pollution and animal health. Fractional passage rates (FPR) of feed are widely used in modern feed evaluation systems and mechanistic rumen models, but data on nutrient-specific FPR are scarce. Such models generally rely on conventional external marker techniques, which do not always describe digesta passage kinetics in a satisfactory manner. Here the use of stable isotope-labelled dietary nutrients as a promising novel tool to assess nutrient-specific passage kinetics is discussed. Some major limitations of this technique include a potential marker migration, a poor isotope distribution in the labelled feed and a differential disappearance rate of isotopes upon microbial fermentation in non-steady state conditions. Such limitations can often be circumvented by using intrinsically stable isotope-labelled plant material. Data are limited but indicate that external particulate markers overestimate rumen FPR of plant fibre compared with the internal stable isotope markers. Stable isotopes undergo the same digestive mechanism as the labelled feed components and are thus of particular interest to specifically measure passage kinetics of digestible dietary nutrients.

Stable Isotope Labeled n-Alkanes to Assess Digesta Passage Kinetics through the Digestive Tract of Ruminants

We describe the use of carbon stable isotope (13C) labeled n-alkanes as a potential internal tracer to assess passage kinetics of ingested nutrients in ruminants. Plant cuticular n-alkanes originating from intrinsically 13C labeled ryegrass plants were pulse dosed intraruminally in four rumen-cannulated lactating dairy cows receiving four contrasting ryegrass silage treatments that differed in nitrogen fertilization level (45 or 90 kg nitrogen ha−1) and maturity (early or late). Passage kinetics through the gastrointestinal tract were derived from the δ13C (i.e. the ratio 13C:12C) in apparently undigested fecal material. Isotopic enrichment was observed in a wide range of long-chain n-alkanes (C27–C36) and passage kinetics were determined for the most abundant C29, C31 and C33 n-alkanes, for which a sufficiently high response signal was detected by combustion isotope ratio mass spectrometry. Basal diet treatment and carbon chain length of n-alkanes did not affect fractional passage rates from the rumen (K 1) among individual n-alkanes (3.71–3.95%/h). Peak concentration time and transit time showed a quantitatively small, significant (p≤0.002) increase with carbon chain length. K 1 estimates were comparable to those of the 13C labeled digestible dry matter fraction (3.38%/h; r = 0.61 to 0.71; p≤0.012). A literature review has shown that n-alkanes are not fermented by microorganisms in the rumen and affirms no preferential depletion of 13C versus 12C. Our results suggest that 13C labeled n-alkanes can be used as nutrient passage tracers and support the reliability of the δ13C signature of digestible feed nutrients as a tool to measure nutrient-specific passage kinetics.

Nutritional impact on health and performance in intensively reared rabbits

The present work summarizes research related to the definition of nutrient recommendations for feeds used in the intensive production of rabbit's meat. Fibre is the main chemical constituent of rabbit diets that typically contain 320 to 360 and 50 to 90 g/kg of insoluble and soluble fibre, respectively. Instead, the dietary contents of cereal grains (∼120 to 160 g/kg), fat (15 to 25 g/kg) and protein concentrates (150 to 180 g/kg) are usually low with respect to other intensively reared monogastric animals. Cell wall constituents are not well digested in rabbits, but this effect is compensated by its stimulus of gut motility, which leads to an increasing rate of passage of digesta, and allows achieving an elevated dry matter intake. A high feed consumption and an adequate balance in essential nutrients are required to sustain the elevated needs of high-productive rabbits measured either as reproductive yield, milk production or growth rate in the fattening period. Around weaning, pathologies occur in a context of incomplete development of the digestive physiology of young rabbits. The supply of balanced diets has also been related to the prevention of disorders by means of three mechanisms: (i) promoting a lower retention time of the digesta in the digestive tract through feeding fibre sources with optimal chemical and physical characteristics, (ii) restricting feed intake after weaning or (iii) causing a lower flow of easily available substrates into the fermentative area by modifying feed composition (e.g. by lowering protein and starch contents, increasing its digestibility or partially substituting insoluble with soluble fibre), or by delaying age at weaning. The alteration in the gut microbiota composition has been postulated as the possible primary cause of these pathologies.

δ13C as a marker to study digesta passage kinetics in ruminants: a combined in vivo and in vitro study

The aim of the current study was to explore the use of the tracer 13C as an internal marker to assess feed fraction-specific digesta passage kinetics through the digestive tract of dairy cows. Knowledge on feed-specific fractional passage rates is essential to improve estimations on the extent of rumen degradation and microbial protein efficiency; however, this information is largely lacking. An in vivo and in vitro experiment was conducted with grass silages (Lolium perenne L.) that were enriched with 13C by growing the grass under elevated 13CO2 conditions. In a crossover design, two dairy cows received pulse doses of two 13C-enriched grass silages and chromium-mordanted neutral detergent fibre (Cr-NDF) into the rumen. The two 13C-enriched grass silages used differed in digestibility and were grown under identical field conditions as the bulk silages fed to the animals. Faecal excretion patterns of 13C-enriched dry matter (13C-DM), neutral detergent fibre (13C-NDF) and Cr-NDF were established, and a nonlinear multicompartmental model was used to determine their rumen passage kinetics. In addition, the 13C-enriched silages were incubated in rumen liquid in an in vitro batch culture system at different time intervals to determine the effect of fermentation on 13C-enrichment in the residue. The in vitro study showed that the 13C : 12C ratios in DM and NDF residues remained stable from 24 h of incubation onwards. In addition, in vitro fractional degradation rates for 12C in the DM and NDF did not differ from those of 13C, indicating that fermentative degradation does not affect the 13C : 12C ratio in the DM nor in the NDF fraction of the residue. Model fits to the faecal excretion curves showed a significant difference in fractional rumen passage rates between Cr-NDF, 13C-DM and 13C-NDF (P ⩽ 0.025). Silage type had no clear effect on rumen passage kinetics (P ⩾ 0.081). Moreover, it showed that peak enrichments for 13C-DM and 13C-NDF in faeces were reached at 30.7 and 41.7 h post dosing, respectively. This is well after the time (24 h) when the 13C : 12C ratios of the in vitro unfermented residues have reached stable enrichment level. Fractional rate constants for particle passage from the rumen are estimated from the descending slope of faecal excretion curves. The present study shows that the decline in 13C : 12C ratio after peak enrichment is not affected by fermentative degradation and therefore can be used to assess feed component-specific fractional passage rates.

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

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

Starch and fiber properties affect their kinetics of digestion and thereby digestive physiology in pigs

Traditionally in swine nutrition, analyses of starch and fiber have focused on assessing quantity; however, both have a wide range of functional properties making them underappreciated nutrients. Starch ranging from low to high amylose changes from rapidly digestible in the upper gut to poorly digestible but fermentable in the lower gut thereby changing from a source of glucose to VFA source. Likewise, fibers ranging from low to high viscosity affect digesta flow and from slowly to rapidly fermentable alter production of VFA serving as energy for the gut or whole body. Our hypothesis is that total extent, kinetics, and site of digestion or fermentation of starch and fiber are important for whole body nutrient use and intestinal health. To elucidate their effects, we developed in vitro, lab-based methodologies to describe kinetics of digestion and fermentation and linked these with in vivo models including i) ileum cannulation to collect digesta, ii) portal-vein catheterization to sequentially sample blood, iii) slaughter method to collect site-specific intestinal tissue and digesta, and iv) indirect calorimetry. Using these methods, kinetics of nutrient absorption was associated with pancreatic and intestinal hormones released into the portal vein, intestinal microbiota, and gene expression in intestinal tissue and microbiota. These studies confirmed that slowly digestible starch is partially degraded in the distal small and large intestine and fermented into VFA including butyrate (10-fold increase in net portal appearance), which reduces insulin responses by 60% and whole body energy use. Starch entering the distal intestine altered mRNA abundance of nutrient transporters and was bifidogenic. Extremely viscous purified fiber dampened glycemic responses and reduced digesta passage rate by 50% thereby increasing ileal digestion of dietary nutrients whereas increased fiber in feed grains reduced nutrient digestibility. Fermentable fiber increased butyrate and insulin production. These methods will therefore support elucidation of mechanisms that link starch and fiber properties to whole body nutrient use and intestinal health.

A pilot study on the ontogeny of digestive physiology in Japanese macaques (Macaca fuscata)

An assumption based on the Jarman–Bell principle suggests a positive relationship between body size and the digestive efficiency in animals, where smaller animals are less effective at digesting fibrous food due to shorter digesta passage. To examine the effect of body size within a species and explore a potential physiological background of ontogenetic diet shifts, we measured food intake, digestibility, digesta passage and gut fill in nine Japanese macaques, including three juveniles/subadult animals. Although these three showed a comparable digestive efficiency as the older animals on a low-fiber diet, they did not achieve the long retention times of adults in spite of similar levels of indigestible food intake and gut capacity. While the limited sample size would not allow generalized conclusions on ontogenetic digestive development in primates, this study suggests additional, yet unexplored effects other than food intake, digestion and gut capacity on digesta retention during ontogeny.

Frothy bloat in ruminants: Cause, occurrence, and mitigation strategies

A number of pasture and feedlot management practices and feed additives have reduced, but not eliminated the occurrence of frothy bloat in cattle. Bloat occurs as a result of complex interactions among the feed, rumen microbial populations and the host. Factors such as soluble protein levels in the feed, rates of feed digestion, bacterial slime production and digesta passage rates, all play a role in the likelihood of bloat. Practices that lower soluble protein levels and retard the rate of feed digestion can reduce the risk of bloat as can grazing alfalfa at advanced stages of maturity. Similarly, processing grain to an optimal particle size, inclusion of ionophores in the diet and allowing a period of adaptation during the transition from forage to grain diets lowers the incidence of feedlot bloat. Pluronic detergents which disperse the stable froth in the rumen can be effective in the treatment and prevention of both pasture and feedlot bloat. The sporadic and unpredictable nature of frothy bloat often makes it unrealistic for preventative measures to be applied to all animals at risk. Genetic engineering of condensed tannin containing, bloat-safe varieties of alfalfa and clover may eliminate the occurrence of bloat in cattle grazing these forages. Understanding the factors that regulate intake and contribute to bacterial slime production could provide additional insight into feedlot bloat. Comparing of the rumen microbial metagenomes and metatrascriptomes of bloated and non-bloated animals should provide a fresh perspective on the role of rumen microbial populations in bloat. The key to the successful prevention of frothy bloat lies in a thorough understanding of the feed, microbial and host factors involved in the condition.

Extent and method of grinding of sorghum prior to inclusion in complete pelleted broiler chicken diets affects broiler gut development and performance

A broiler experiment was conducted to examine the effects of sorghum particle size and milling type on the performance, nitrogen corrected apparent metabolisable energy (AME n), digestive tract development, digesta pH, duodenal digesta particle size and digesta passage rate. Complete pelleted diets with identical botanical and chemical composition containing 750 g/kg whole sorghum (WS), sorghum ground through hammer mill with 1 mm and 3 mm screen (HM1 and HM3) and sorghum ground on a roller mill with 0.15 mm spacing (RM0.15), were made. Sorghum for diets HM3 and RM0.15 were milled to approximately the same mean particle size. Diet WS resulted in poorer (P<0.05) weight gain and feed conversion ratio (FCR) than the other diets from 11 to 21 days of age, while diet RM0.15 resulted in improved FCR. Apparent ME n determined between 25 and 28 days of age, however, was higher (P<0.05) for diet WS than for the other diets. This was possibly due to a longer adaptation time to a larger feed particle size, as indicated by a lower (P<0.05) pH in the gizzard and smaller duodenal digesta particle size for this diet. Diet HM1 gave similar performance as diet HM3, but resulted in a significantly smaller gizzard, a higher pH of the gizzard content, a lower pH of the duodenal content and larger particles in the duodenal contents, thus indicating that gizzard development and activity were compromised by this diet. Total tract passage rate of the liquid phase marker was slower (P<0.05) in the WS fed birds, but there were no differences in solid phase marker excretion rates.

Effects of viscosity and fermentability of dietary fibre on nutrient digestibility and digesta characteristics in ileal-cannulated grower pigs

Relative contributions of two functional properties, viscosity and fermentability of dietary fibre, on apparent ileal digestibility (AID), apparent total tract digestibility (ATTD), digesta passage rate, N retention and SCFA concentration have not been established. Thus, eight ileal-cannulated pigs randomised in a double 4 × 4 Latin square were fed four diets based on maize starch and casein supplemented with 5 % of actual fibre in a 2 × 2 factorial arrangement: low-fermentable, low-viscous cellulose (CEL); low-fermentable, high-viscous carboxymethylcellulose (CMC); high-fermentable, low-viscous oat β-glucan (LBG); high-fermentable, high-viscous oat β-glucan (HBG). Viscosity and fermentability interacted to affect (P < 0·001) digesta viscosity and AID and ATTD of nutrients. These properties tended to interact to affect (P < 0·10) digesta passage rate and butyrate. Pigs fed the CMC diet had the lowest (P < 0·05) digesta passage rate and the highest (P < 0·001) AID of energy, crude protein and DM, and ATTD of energy and DM. Post-ileal DM digestibility was highest (P < 0·001) for pigs fed the CEL and HBG diets. Post-ileal DM digestibility had a negative, curvilinear relationship with the AID of energy and crude protein (R2 0·85 and 0·72, respectively; P < 0·001). Digesta viscosity had a less strong relationship with the AID of energy and crude protein (R2 0·45 and 0·36, respectively; P < 0·001). In conclusion, high-viscous, low-fermentable dietary fibre increases the proportion of a diet that is digested in the small intestine by reducing digesta passage rate.

RUMINANT NUTRITION SYMPOSIUM: Productivity, digestion, and health responses to hindgut acidosis in ruminants1

Microbial fermentation of carbohydrates in the hindgut of dairy cattle is responsible for 5 to 10% of total-tract carbohydrate digestion. When dietary, animal, or environmental factors contribute to abnormal, excessive flow of fermentable carbohydrates from the small intestine, hindgut acidosis can occur. Hindgut acidosis is characterized by increased rates of production of short-chain fatty acids including lactic acid, decreased digesta pH, and damage to gut epithelium as evidenced by the appearance of mucin casts in feces. Hindgut acidosis is more likely to occur in high-producing animals fed diets with relatively greater proportions of grains and lesser proportions of forage. In these animals, ruminal acidosis and poor selective retention of fermentable carbohydrates by the rumen will increase carbohydrate flow to the hindgut. In more severe situations, hindgut acidosis is characterized by an inflammatory response; the resulting breach of the barrier between animal and digesta may contribute to laminitis and other disorders. In a research setting, effects of increased hindgut fermentation have been evaluated using pulse-dose or continuous abomasal infusions of varying amounts of fermentable carbohydrates. Continuous small-dose abomasal infusions of 1 kg/d of pectin or fructans into lactating cows resulted in decreased diet digestibility and decreased milk fat percentage without affecting fecal pH or VFA concentrations. The decreased diet digestibility likely resulted from increased bulk in the digestive tract or from increased digesta passage rate, reducing exposure of the digesta to intestinal enzymes and epithelial absorptive surfaces. The same mechanism is proposed to explain the decreased milk fat percentage because only milk concentrations of long-chain fatty acids were decreased. Pulse-dose abomasal fructan infusions (1 g/kg of BW) into steers resulted in watery feces, decreased fecal pH, and increased fecal VFA concentrations, without causing an inflammatory response. Daily 12-h abomasal infusions of a large dose of starch (~4 kg/d) have also induced hindgut acidosis as indicated by decreased fecal pH and watery feces. On the farm, watery or foamy feces or presence of mucin casts in feces may indicate hindgut acidosis. In summary, hindgut acidosis occurs because of relatively high rates of large intestinal fermentation, likely due to digestive dysfunction in other parts of the gut. A better understanding of the relationship of this disorder to other animal health disorders is needed.

Relationships between chewing behavior, digestibility, and digesta passage kinetics in steers fed oat hay at restricted and ad libitum intakes1

The objective of this study was to evaluate the relationships between chewing behavior, digestibility, and digesta passage kinetics in steers fed oat hay at restricted and ad libitum intakes. Four Hereford steers, with an initial average BW of 136 kg, were used in an experiment conducted as a balanced 4 × 4 Latin square with 4 treatments (levels of intake) and 4 periods. Animals were fed lopsided oat hay (Avena strigosa Schreb.) at 4 levels of intake (as a percentage of BW): 1.5, 2.0, 2.5, and ad libitum. Digestibility, chewing behavior, and digesta passage kinetic measurements were recorded during the experimental period. Chewing rates during eating and ruminating [(chews•min(-1))/g of DMI•kg(-1) of BW•d(-1)] decreased (P = 0.018 and P = 0.032, respectively) with increased DMI (g•kg(-1) of BW•d(-1)), whereas total chewing and total time spent on each chewing activity increased. Calculated total energy expended by the chewing activity was 4.2, 4.4, 5.2, and 5.3% of ME intake for DMI of 1.5, 2.0, and 2.5% of BW and ad libitum, respectively, indicating that adjustments in animal chewing behavior may be a mechanism of reducing energy expenditure when forages are fed at restricted intake. Hay digestibility decreased (P < 0.001) with increased DMI (r = -0.865). Digesta mean retention time (h) was strongly correlated with DMI (r = -0.868) and OM digestibility (r = 0.844). At reduced intake, hay digestibility was enhanced (P < 0.001) by extending digesta retention time and by increasing chewing efficiency, highlighting the relationship between chewing behavior and the digestive process. Fractional outflow rate of particulate matter from the reticulorumen (k(1)) was positively correlated with total chews, emphasizing that the decrease in particle size caused by chewing facilitates particle flow through the digestive tract. Increased hay intake also increased (P < 0.001) k(1), whereas passage rate of the liquid phase, transit time, and rumen fill were not affected (P > 0.05). The latter was correlated with rumen volume (r = 0.803). In conclusion, the results of this study indicate that animals fed at restricted intake increased chewing rate when eating and ruminating, which, along with a longer digesta retention time, contributed to enhance feed digestibility.

Digesta Passage Time, Digestibility, and Total Gut Fill in Captive Japanese Macaques (Macaca fuscata): Effects Food Type and Food Intake Level

Digestion is an important process in understanding the feeding ecology of animals. We examined digesta passage time, digestibility, and total gut fill in Japanese macaques (Macaca fuscata; n = 4) under 4 dietary conditions representing the seasonal and regional variations in the diets of wild populations to determine the effects of food type and food intake on these digestive features. Food type is associated with mean retention time (MRT), digestibility, and total gut fill. Dry matter intake (DMI) of food correlates positively with total gut fill but not with MRT or digestibility. Conversely, indigestible DMI affected MRT negatively. Thus, when Japanese macaques consume high-fiber foods, MRT becomes shorter and digestibility is lower than when eating low-fiber foods. Moreover, macaques experience increases in total gut fill when they consume high-fiber diets or a large amount of food. Japanese macaques may excrete difficult-to-digest food components quickly; they nevertheless buffer an increase in food intake by an increase in gut fill. Our study offers new insights into the relationship between feeding ecology and nutritional physiology in primates by simultaneously examining the effects of food type and intake level on MRT and digestibility.

Effect of Environmental Factors and Influence of Rumen and Hindgut Biogeography on Bacterial Communities in Steers

Feces from cattle production are considered important sources of bacterial contamination of food and the environment. Little is known about the combined effects of arctic temperatures and fodder tannins on rumen and hindgut bacterial populations. Individual rumen liquor and rectal fecal samples from donor steers fed either alfalfa silage or sainfoin (Onobrychis viciifolia Scop.) silage and water ad libitum were collected weekly on the first three sampling days and fortnightly afterwards. The daily ambient temperatures were registered and averaged to weekly mean temperatures. Steers fed sainfoin silage had lower (P < 0.05) concentrations of branched-chain volatile fatty acids (VFA) than those fed alfalfa silage. All VFA concentrations were higher (P < 0.001) in rumen liquor samples than in fecal samples. The interaction of sample type and diet showed a significant effect (P < 0.05) on the proportions of the bacterial community that were from the phyla Proteobacteria and Verrucomicrobia. Ambient temperature had an indirect effect (P < 0.05) on the phylum Firmicutes, as it affected its proportional balance. The bacterial population diversity in samples appeared to decrease concurrently with the ambient temperature. The phylum Firmicutes explained the first principal component at 64.83 and 42.58% of the total variance in rumen liquor and fecal samples, respectively. The sample type had a larger effect on bacterial communities than diet and temperature. Certain bacterial populations seemed to be better adapted than others to environmentally adverse conditions, such as less access time to nutrients due to higher motility and rate of passage of digesta caused by extreme temperatures, or antimicrobials such as tannins, possibly due to an influence of their biogeographical location within the gut.