Digesta Passage Time,Digestibility, and Total Gut Fill in Captive Japanese Macaques (<Emphasis Type="BoldItalic">Macaca fuscata</Emphasis>): 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.     

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.     

Initial studies on the contributions of body size and gastrointestinal passage rates to dietary flexibility among gorillas

Large body size has been traditionally seen as the primary dietary adaptation of gorillas, facilitating their consumption of fibrous foods (Schaller ?1963 The Mountain Gorilla; Watts ?1990 Int. J. Primatol. 11:21-45). Nevertheless, recent research has emphasized frugivory among western lowland gorillas, as well as the influence of habitat and seasonality on gorilla diet and behavior across subspecies (Watts ?1990 Int. J. Primatol. 11:21-45; Tutin et al. ?1991 Philos. R. Soc. Trans. Lond. Biol. 334:179-186; Remis ?1994 Ph.D. Thesis, ?1997a Am. J. Primatol. 43:87-109, ?1997b Am. J. Primatol. 43:111-133, ?1998 Primate Locomotion: Recent Advances, p 95-(1)108, ?1999 Primates 40:383-396; Nishihara ?1995 Primates 36:151-168; Goldsmith ?1999a Int. J. Primatol. 20:1-23, Goldsmith [1999b] Nonhuman Primates, p 58-63). This study provides preliminary data to address the physiological underpinnings of dietary flexibility among gorillas, and their consumption of a broad range of fibrous and tannin-rich foods. To date, little is known about the digestive physiology of the African apes (but see Milton ?1984 Adaptations for Foraging in Nonhuman Primates, p 249-279, Milton [1984] ?1999Evol. Anthropol. 8:11-20; Milton and Demment ?1988 J. Nutr. 118:1082-1088; Lambert ?1997 Ph.D. Dissertation), although gastrointestinal morphology and proportions are roughly similar among species ( Chivers and Hladik ?1980 J. Morphol. 166:337-386). This study provides additional experimental data on the gastrointestinal passage times of gorillas (Gorilla gorilla gorilla) fed a captive diet in a zoological park setting and discusses results in relation to field research on gorilla feeding ecology. In this study, 480 small plastic markers were fed to six captive gorillas. The mean gut retention time (MRT) of the adult gorillas in this study was 50 hr, longer than the 31 hr reported for chimpanzees fed a similar diet (Lambert ?1997 Ph.D. Dissertation). These data suggest that gorillas may retain foods in their gastrointestinal tracts longer than smaller hominoids, and that the large body size likely forms the primary basis for consumption of fiber. This research provides additional data to contribute to our understanding of the relationships of body size and morphology to ecology, and the evolution of body size, foraging strategy and social organization among the African apes.     

Use of total dietary fiber across four lemur species (Propithecus verreauxi coquereli,Hapalemur griseus griseus,Varecia variegata,and Eulemur fulvus): Does fiber type affect digestive efficiency?

In vivo digestibility and transit of two experimental diets were compared across four lemur species for which gastrointestinal morphology and preliminary data on physiology differ:Varecia variegata (VV), Eulemur fulvus (EF), Propithecus verreauxi (PV), and Hapalemur griseus (HG). Since free-ranging groups consume varied amounts of slowly fermentable insoluble fiber (IF) and rapidly fermentable soluble fiber (SF), differences in digestibility may be related to variation in the fiber types consumed. To investigate this, two diets were designed to provide 28% of dry matter (DM) as total dietary fiber (TDF). The ratio of IF/SF (g/g) differed across the diets (12.15:1 for the IF diet, and 3.76:1 for the IF/SF diet). The DM digestibility (DMD) of both diets differed across species: DMD was lower for EF and VV (approximately 56-58%), and higher for PV (72%) and HG (76%). The fiber digestibility results were as follows: TDF digestibility was similar for VV and EF (23% and 28%), higher for PV (56%), and highest for HG (66%). IF digestibility was lower for VV and EF (20% and 28%), and higher for PV and HG (53% and 62%). The transit times (TTs) of the two markers Cr and Co were similar (approximately 3.5 hr for VV and EF, 25 hr for PV, and 30 hr for HG). The mean retention times (MRTs) showed the same trend. The results from these captive groups suggest there are large differences in digestive efficiency that are likely related to the varied fiber composition of the free-ranging diet, and the amount of time the digesta are retained in the gut.     

Effects of dietary fibre on digesta passage, nutrient digestibility, and gastrointestinal tract morphology in the granivorous Mongolian gerbil (Meriones unguiculatus)

To investigate digestive tract performance in Mongolian gerbils (Meriones unguiculatus), food intake and digestibility, digesta passage rate, and gastrointestinal tract morphology were measured in captive animals fed low- or high-fibre diets. We used two markers (Co-ethylene diamine tetra-acetic acid for solutes and Cr-mordanted cell walls for particles) to measure differential passage rates of digesta fractions in order to test for the presence of a colonic separation mechanism (CSM). Although dry-matter intakes on the high-fibre diet did not differ from those on the low-fibre diet, digestibilities of dry matter, neutral-detergent fibre, acid-detergent fibre, crude protein, and crude fat were all significantly lower on the high-fibre diet. Gross energy intake on the high-fibre diet also did not differ from that on the low-fibre diet, but energy lost in faeces was much higher than on the low-fibre diet; thus, energy digestibility and digestible energy intake were significantly lower on the high-fibre diet. The lengths and dry-tissue masses of all segments of the gastrointestinal tract tended to enlarge in response to increased dietary fibre, but only the total tract contents, contents of the small intestine, and length and dry-tissue mass of the caecum increased significantly. The mean retention time (MRT) of the particle marker was significantly greater than that of the solute marker on the low-fibre but not the high-fibre diet; the solute/particle differential retention ratio was 0.62 on the low-fibre diet and 0.90 on the high-fibre diet. Thus, there was no evidence for selective retention of the solute marker on either diet. The MRT of the particle marker was significantly lower on the high-fibre diet and in the same direction as the MRT of the solute marker. These results suggest that the granivorous Mongolian gerbil has no CSM but can adjust its digestive tract capacity to accommodate greater quantities of low-quality food.     

Digestive performance and selective digesta retention in the long-nosed bandicoot,Perameles nasuta,a small omnivorous marsupial

Bandicoots are opportunistic omnivores that feed on invertebrates, fungi and both epigeal and hypogeal plant parts. We examined the performance of the digestive tract of the long-nosed bandicoot (Perameles nasuta) in terms of intake and total digestibility, patterns of excretion of inert digesta markers, and likely sites of digesta retention, on two diets designed to mimic part of their natural plant and insect diets. On the insect diet (mealworm larvae), bandicoots virtually maintained body mass at a digestible energy intake of 511 kJ · kg^-0.75 · day^-1 and were in strongly positive nitrogen balance. In contrast, on the plant diet (shredded sweet potato), bandicoots ate only one-third as much digestible energy, lost 7% body mass, and were in negative nitrogen balance. Mean retention times of two particle markers on the plant diet (27.5 and 27.0 h) were more than double those on the insect diet (12.4 and 11.2 h), and on both diets the mean retention time of the fluid digesta marker was greater than those of the particle markers, indicating consistent selective retention of fluid digesta in the gut. It was seen radiographically than in mealwormfed bandicoots major sites of digesta retention were the distal colon and rectum, whereas in the sweet potato-fed animals the caecum and proximal colon were principal sites. It was concluded that retention of plant material in the caecum and proximal colon (the main sites of microbial digestion) and the preferential retention of fluid digesta (together with bacteria and small feed particles) in the caecum were important factors in the ability of bandicoots to switch between insect and plant foods, depending on relative availabilities, and thus to exploit nutritionally unpredictable environments.Abbreviations ADF acid-detergent fibre - bm body mass - Co-ED-TA cobalt-ethylenediaminetetra-acetic acid - CWC cell wall constituents - DE digestable energy - dm dry matter - EUN endogenous urinary nitrogen - ICP inductively-coupled plasma atomic emission spectroscopy - MFN metabolic faecal nitrogen - MRT mean retention time - NDF neutral-detergent fibre - ww wet weight     

The role of taste in food selection by African apes: implications for niche separation and overlap in tropical forests

Ripe fruit eating shapes the behavior of most of the apes. Gorillas (Gorilla gorilla) and chimpanzees (Pan troglodytes) are very different sizes and, consequently, have been traditionally viewed as ecologically distinct, but few studies have explored the behavioral and physiological foundations of their diets. Debate continues on the extent that large-bodied gorillas may be less selective and more opportunistic fruit eaters than chimpanzees. Taste responses have been predicted to relate to body size and digestive strategies. This study employs laboratory research on taste perception and discrimination among captive zoo-housed chimpanzees and relates it to previous work on gorillas to better characterize diets and niche separation among these apes. During the captive trials, differences were recorded in consumption patterns of water and varying concentrations of dilute aqueous fructose (sweet) and tannic acid solutions (astringent), compounds commonly found in wild foods. The chimpanzees exhibited similar preference thresholds for fructose (50 mM) to other primates studied. They exhibited slightly lower inhibition thresholds for tannic acid solutions than gorillas, but higher than smaller primates studied to date. These preliminary findings suggest that tannin tolerance may well be mediated by body size, though possible species differences in salivary proteins or other sensory differences remain to be explored. This research furthers our efforts to understand the roles of body size and physiological adaptations in shaping diet and niche separation of chimpanzees and gorillas.     

Digestive Retention Times in Forest Guenons (Cercopithecus spp.) with Reference to Chimpanzees (Pan troglodytes)

Because the length of time food is maintained in the gut influences fermentation rates and its overall digestibility, information on digestive passage rates is critical to explain the overall feeding and foraging strategy of a species. I present results from digestive passage experiments conducted on captive Cercopithecus ascanius, C. mitis, C. neglectus, Miopithecus talapoin, and Pan troglodytes. I recorded several measures of digestive passage time, including transit time (time of first marker appearance; TT), mean retention time of markers (MRT), and time of last appearance of a marker (TLA). I conducted 4 trials on each of the 10 subjects. A trial consists of the administration of 20, non-toxic colored plastic markers. Overall, the 5 species varied in digestive times (p < 0.01), but there is no difference between Cercopithecus neglectus and Pan troglodytes (p = 0.131) or between C. mitis and C. ascanius (p = 0.661). When the effect of body size is removed (by computing the ratio y/x, where x = body mass, and y = MRT), Pan troglodytes exhibits a low ratio, suggesting relatively slow retention times in the 4 cercopithecines. My findings and other published digestive passage rates suggest that lengthy digestive retention times may be characteristic of cercopithecines. These data may help to interpret how the smaller-bodied guenons are able to consume a higher percentage of fiber than that of chimpanzees, a specialized frugivore. Small body size, in combination with long digestive passage times may be an adaptation on the part of Cercopithecus species to consume a high fiber diet, while maintaining a greater capacity to detoxify secondary metabolites.     

A comparative study of digestion in North Atlantic seabirds

We present data on digestive efficiencies and gut retention times of eight North Atlantic seabird species, fed on two fish species – lesser sandeel Ammodytes marinus and whiting Merlangius merlangus – which commonly occur in the diet of wild seabirds. In an interspecific comparison, there was a positive relationship between retention time and digestive efficiency, which we suggest represents a trade-off between conflicting benefits of efficient digestion and rapid digestion. Analysis of excretion curves revealed that retention time of digesta in the stomach was more important than passage time of digesta through the intestine in determining whole gut retention time. Differences in stomach retention time of lesser sandeel and whiting explained the longer overall retention time of the latter diet. Stomach retention time and whole gut retention time were greater in species with relatively large stomachs, while intestine passage time was correlated with relative intestine length. Species which typically eat a wide range of food types, including low quality items, tended to have slow and efficient digestion and heavy stomachs, whereas species which specialise on readily digestible and energy dense food types had the opposite digestion strategy.     

Food Preferences Among Captive Western Gorillas (Gorilla gorilla gorilla) and Chimpanzees (Pan troglodytes)

I used a zoological park setting to address food preferences among gorillas (Gorilla gorilla gorill) and chimpanzees (Pan troglodytes). Gorillas and chimpanzees are different sizes, and consequently, have been traditionally viewed as ecologically distinct. Sympatric western gorillas and chimpanzees have proved difficult to study in the wild. Limited field data have provided conflicting information about whether gorillas are fundamentally different from chimpanzees in diet and behavior. Fruit eating shapes the behavior of most apes, but it is unclear whether the large-bodied gorillas are an exception to this rule, specifically whether they are less selective and more opportunistic fruit eaters than chimpanzees are. My research provides experimental observational data to complement field data and to better characterize the diets and food preferences of the African apes. During laboratory research at the San Francisco Zoological Gardens, I examined individual and specific differences in food preferences of captive gorillas and chimpanzees via experimental paired-choice food trials with foods that varied in nutritional content. During the study, I offered 2500 paired-food choices to 6 individual gorillas and 2000 additional pairs to them as a group. I also proffered 600 food pairs to 4 individual chimpanzees. Despite expectations of the implications of body size differences for diet, gorillas and chimpanzees exhibited similar food preferences. Both species preferred foods high in non-starch sugars and sugar-to-fiber ratios, and low in total dietary fiber. Neither species avoided foods containing tannins. These data support other suggestions of African apes sharing a frugivorous adaptation.     

Digestive strategy of the asian colobine genusTrachypithecus

The Asian colobines,Trachypithecus obscurus andT. cirstantus, eat plant-based diets containing 55–80% leaves. The structural polysaccharides in leaves and other plant parts require microbial fermentation before they can be used as an energy source by the monkeys. The major compartments of the gastro-intestinal tract ofTrachypithecus are a voluminous haustrated stomach, a long small itnestine and capacious haustrated hindgut, all of which contribute to the digestive strategy of these two species. Results of digesta marker passage studies indicate there is prolonged retention of digesta for fermentation in both the stomach and haustrated colon. The digestive strategy of these colobines is defined as gastro-colic fermentation, unlike that of other forestomach fermenters in which the hindgut fermentation is of secondary importance.     

Variation in digestive efficiency of captive North American river otters (Lontra canadensis) on various diets

Energy content, proximate nutrient values, passage rate, and digestive efficiency associated with various diet types and factors affecting these parameters have not been quantified for the North American river otter (Lontra canadensis). We measured energy digestive efficiency (DEff) and intestinal passage rate of three captive river otters on their regular diet (a combination of polar bear diet, cat food, and feline diet) and on test diets consisting of the constituent components of their regular diet. Gross energy, crude protein, crude fat, and crude fiber varied appreciably among diet components. Caloric DEff values were high (cat food and polar bear diet combination: 83.11%; regular diet: 86.62%; feline diet: 90.22%) indicating diets high in fat and protein permit greater energy absorption. Passage rates ranged from 167–188 minutes and were influenced by level of activity such that passage rate was more rapid at higher levels of activity. Coefficients of variation (CV) from DEff (CV=1.51) and digesta passage rates (CV=7.35) were dissimilar, indicating that a direct measure may yield a more precise estimate of absorption over digesta passage rates. To further understand energy handling by river otters on diets used in zoologic institutions and to better provide the nutrient dense diets this active species requires, additional studies quantifying energetic parameters for captive otters of various genders, ages, and reproductive conditions on other diet types are needed. Zoo Biol 0: 1–10, 2007. © 2006 Wiley‐Liss, Inc.     

Multiple pathways from three types of sugar receptor sites to metabotropic transduction pathways of the blowfly: study by the whole cell-clamp experiments

Differences in the allometric scaling between gut capacity (with body mass, BM^1.00) and food intake (with BM^0.75) should theoretically result in a scaling of digesta retention time with BM^0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman–Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5–180 kg) to a literature data collection. While dry matter gut fill scaled to BM^1.07 and dry matter intake to BM^0.76, digesta mean retention time (MRT) scaled to BM^0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology.     

Harvesting, rumination, digestion, and passage of fruit and leaf diets by a small ruminant, the blue duiker

Because small ruminants (<15 kg) have a high ratio of metabolic rate to fermentation capacity, they are expected to select and require low-fiber, nutrient-dense concentrate diets. However, recent studies suggest that small ruminants may not be as limited in their digestive capacity as previously thought. In this study, we examined harvesting, rumination, digestion, and passage of three diets (domestic figs Ficus carica, fresh alfalfa Medicago sativa, and Pacific willow leaves Salix lasiandra) ranging from 10 to 50% neutral detergent fiber content (NDF) in captive blue duikers (Cephalophus monticola, 4 kg). Harvesting and rumination rates were obtained by observing and videotaping animals on each diet, and digestibility and intake were determined by conducting total collection digestion trials. We estimated mean retention time of liquid and particulate digesta by administering Co-EDTA and forages labelled with YbNO₃ in a pulse dose and monitoring fecal output over 4 days. Duikers harvested and ruminated the fig diet faster than the alfalfa and willow diets. Likewise, they achieved higher dry matter, energy, NDF, and protein digestibility when eating figs, yet achieved a higher daily digestible energy intake on the fresh willow and alfalfa than on the figs by eating proportionately more of these forages. Duikers maintained a positive nitrogen balance on all diets, including figs, which contained only 6.3% crude protein. Mean retention time of cell wall in the duikers’ digestive tract declined with increasing NDF and cellulose content of the diet. Digestibility coefficients and mean retention times of these small ruminants were virtually equivalent to those measured for ruminants two orders of magnitude larger, suggesting that they are well adapted for a mixed diet. Received: 10 August 1999 / Accepted: 16 November 1999     

A diet containing native or fermented wheat bran does not interfere with natural microbiota of laying hens

Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fiber compound for monogastric animals. The aim of this study was to evaluate the influence of native or fermented WB on the gut physiology and microbiology of laying hens. To accomplish this, 24 laying hens were fed the following diets: conventional diet without WB; 15% native WB in the diet; 15% WB fermented with Pleurotus eryngii; and 15% WB fermented with P. eryngii and a lactic acid bacterial culture. Immediately after slaughtering, digesta samples were taken from the jejunum, ileum and cecum, respectively. Total DNA was extracted and subsequently investigated with 16S DNA amplicon sequencing. Neither native nor fermented WB supplementations negatively affected the feed conversion ratio, laying performance or the relative abundances and alpha-diversity of microbiota in the intestine. Effects of WB-based diets on gut morphology were only recognized in the jejunum (reduced villum height and mucosa thickness). Likewise, WB supplementation decreased the digestibility of DM and starch. Based on these findings, it was demonstrated that different WB variants are applicable without exerting practically negative consequences on performance or on gut microbiota. Fermentation improved the digestibility/retention of dietary fat and phosphorus. However, no further beneficial effects were observed. This study also allowed a more in-depth view on the laying hens’ gut microbiome and its variation within the gut segments.     

Food consumption and retention time in captive whooping cranes (Grus americana)

Food consumption, digesta retention time, and food preference were measured for captive whooping cranes fed pelleted diets. The basal commercial diet was compared to four mixtures containing 70% basal and 30% of one of four important winter foods for the whooping crane: blue crab (Callinectes sapidus), wolfberry fruit (Lycium carolinianum), live oak acorn (Quercus virginiana), or common Rangia clam (Rangia cuneata). Because captive birds would not eat whole foods, we were prevented from direct food preference tests. Food passed through the gut rapidly, with almost complete elimination within 7 hr. There was some indication that retention time was shorter for the low fiber and high ash and calcium clam diet. Cranes ate less wolfberry feed (g/day) than the other feeds, and all birds ate less wolfberry feed on the day it was first fed, compared to basal diet the previous day. Birds ate more low energy feed than high energy feed. Due to combined effects of low energy content, lower metabolizable energy coefficients, and reduced feed consumption, less energy was assimilated for study diets than basal diet. Apparent shorter retention times for some diets containing whooping crane foods may partly explain lower digestibilities and metabolizable energy of winter whooping crane foods compared to commercial crane diet. Zoo Biol 16:519–531, 1997. © 1997 Wiley-Liss, Inc.     

Digestive constraints on an aquatic carnivore: effects of feeding frequency and prey composition on harbor seals

We hypothesized that increased feeding frequency in captive harbor seals would increase nutrient loads and thus reduce retention time and the digestive efficiency of natural prey. We measured daily feed intake and excretion during 6 feeding trials and fed herring (49% lipid), pollock (22% lipid) or an equal mix of each diet over 24 months. Animals were accustomed to feeding at either high or low frequency. Body mass and intake did not vary with season. Although mean retention times were similar between diets and feeding frequencies, solute and particulate digesta markers separated at high feeding frequency. Consistent dry matter digestibility resulted in greater gut fill from pollock than from herring. Digestible energy intakes from pollock were approximately 25% greater than from either herring or the mixed diet. Lipid digestibility of herring declined from 90% to 50% when lipid intake exceeded 60 g kg^–0.75 day^–1. Our hypothesis of a trade-off between intake and digestion was not supported for protein but was supported for lipid. Results of this study imply that a flexible digestive system for harbor seals can compensate for ingesting prey of lower energy density by increasing gut fill and enhancing protein and lipid assimilation, to sustain digestible energy intake.Abbreviations DM dry matter - DEI digestible energy intake - DIT diet-induced thermogenesis - FF feeding frequency - MRT mean retention time Communicated by: G. Heldmaier     

哺乳动物消化道内食物通过速率的测定方法

通过速率是消化道功能的一个重要量度,通常采用平均滞留时间来描述食物的通过速率。测定平均滞留时间的方法很多,实验条件不同,所采用的测定及计算方法也不同。本文对主要测定方法进行了介绍。     

Digesta passage and functional anatomy of the digestive tract in the desert tortoise (Xerobates agassizii)

The herbivorous tortoise Xerobates agassizii contents with large fluctuations in the quality and abundance of desert pastures. Responses to grass (Schismus barbatus), herbage (Sphaeralcea ambigua) and pelleted diets were studied in captive animals. Digestive anatomy was investigated in wild tortoises. Cornified esophageal epithelia and numerous mucus glands along the digestive tract indicated a resistance to abrasive diets. Gastric contents were acidic whereas hindgut digesta were near neutral pH. The colon was the primary site of fermentation with short-chain fatty acids mainly comprised of acetate (69–84%), propionate (10–15%) and n-butyrate (1–12%). Fibre digestion was extensive and equivalent to 22–64% of digestible energy intakes. Large particles of grass (25 mm Crmordants) were excreted as a pulse but retained longer than either fluids (Co-EDTA) or fine particles (2 mm; Yb). Patterns of marker excretion suggested irregular mixing of only the fluid and fine particulate digesta in the stomach and the colon. Mean retention times of Crmordants were 14.2–14.8 days on the grass and highfibre pellets. Intakes of grass were low and accompanied by smaller estimates of digesta fill than for the high-fibre pellets. Digestive capacity was large and estimated at 11–21% of body mass on these diets. The capacious but simple digestive anatomy of the tortoise may provide the greatest flexibility in utilizing a variety of forages in its unreliable habitat.Abbreviations bm body mass - DM drymatter - EDTA ethylene-diamine tetra-acetic acid - MRT mean retention time - NDF neutral detergent fibre - SCFA short-chain fatty acid(s) - T _max time to maximum marker concentration     

The effect of captivity on the primate gut microbiome varies with host dietary niche

Despite careful attention to animal nutrition and wellbeing, gastrointestinal distress remains relatively common in captive non‐human primates (NHPs), particularly dietary specialists such as folivores. These patterns may be a result of marked dietary differences between captive and wild settings and associated impacts on the gut microbiome. However, given that most existing studies target NHP dietary specialists, it is unclear if captive environments have distinct impacts on the gut microbiome of NHPs with different dietary niches. To begin to examine this question, we used 16S ribosomal RNA gene amplicon sequences to compare the gut microbiomes of five NHP genera categorized either as folivores (Alouatta, Colobus) or non‐folivores (Cercopithecus, Gorilla, Pan) sampled both in captivity and in the wild. Though captivity affected the gut microbiomes of all NHPs in this study, the effects were largest in folivorous NHPs. Shifts in gut microbial diversity and in the relative abundances of fiber‐degrading microbial taxa suggest that these findings are driven by marked dietary shifts for folivorous NHPs in captive settings. We propose that zoos and other captive care institutions consider including more natural browse in folivorous NHP diets and regularly bank fecal samples to further explore the relationship between NHP diet, the gut microbiome, and health outcomes.