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.     

The relative merits of foregut and hindgut fermentation

Mammalian herbivores cannot break down cellulose except by fermentation, and may have Termentation chambers at either end of the gut: ruminants have their principal fermentation chamber in the stomach but horses ferment only in the hindgut. A mathematical model (Alexander, 1991) predicted that foregut fermenters should do better than hindgut fermenters on poor foods, and the reverse on richer. less fibrous foods. Further, the optimum gut for poor foods would have the hindgut fermentation chamber only a little smaller than the foregut chamber. However. it has been claimed that horses do better than ruminants on poor food, and the hindgut of ruminants is much smaller than the rumen.
In this paper, the basic model is modified in ways designed to make it more realistic and the effects are investigated. None of the modifications alters the conclusion that the optimum gut for poor food has a large foregut fermentation chamber. However, the optimum proportions of fore-to hindgut, for poor diets, become more like those of real ruminants when account is taken of the diminishing volume of the food passing through the gut, and of incomplete mixing in the rumen.     

Is there an influence of body mass on digesta mean retention time in herbivores? A comparative study on ungulates

The relation between body mass (BM) and digesta mean retention time (MRT) in herbivores was the focus of several studies in recent years. It was assumed that MRT scaled with BM(0.25) based on the isometric scaling of gut capacity (BM(1.0)) and allometric scaling of energy intake (BM(0.75)). Literature studies that tested this hypothesis produced conflicting results, arriving sometimes at higher or lower exponents than the postulated 0.25. This study was conducted with 8 ruminants (n=2-6 per species) and 6 hindgut fermenting species/breeds (n=2-6, warthog n=1) with a BM range of 60-4000 kg. All animals received a ration of 100% grass hay with ad libitum access. Dry matter intake was measured and the MRT was estimated by the use of a solute and a particle (1-2 mm) marker. No significant scaling of MRT(particle) with BM was observed for all herbivores (32 BM(0.04), p=0.518) and hindgut fermenters (32 BM(0.00), p=1.00). The scaling exponent for ruminants only showed a tendency towards significance (29 BM(0.12), p=0.071). Ruminants on average had an MRT(particle) 1.61-fold longer than hindgut fermenters. Whereas an exponent of 0.25 is reasonable from theoretical considerations, much lower exponents were found in this and other studies. The energetic benefit of increasing MRT is by no means continuous, since the energy released from a given food unit via digestion decreases over time. The low and non-significant scaling factors for both digestion types suggest that in ungulates, MRT is less influenced by BM (maximal allometric exponent ≤0.1) than often reported.     

Comparative nutrient extraction from forages by grazing bovids and equids: a test of the nutritional model of equid/bovid competition and coexistence

Summary Ruminants are unevenly distributed across the range of body sizes observed in herbivorous mammals; among extant East African species they predominate, in numbers and species richness, in the medium body sizes (10–600 kg). The small and the large species are all hind-gut fermenters. Some medium-sized hind-gut fermenters, equid perissodactyls, coexist with the grazing ruminants, principally bovid artiodactyls, in grassland ecosystems. These patterns have been explained by two complementary models based on differences between the digestive physiology of ruminants and hind-gut fermenters. The Demment and Van Soest (1985) model accounts for the absence of ruminants among the small and large species, while the Bell/Janis/Foose model accounts both for the predominance of ruminants, and their co-existence with equids among the medium-sized species (Bell 1971; Janis 1976; Foose 1982). The latter model assumes that the rumen is competitively superior to the hind-gut system on medium quality forages, and that hind-gut fermenters persist because of their ability to eat more, and thus to extract more nutrients per day from high fibre, low quality forages. Data presented here demonstrate that compared to similarly sized grazing ruminants (bovids), hind-gut fermenters (equids) have higher rates of food intake which more than compensate for their lesser ability to digest plant material. As a consequence equids extract more nutrients per day than bovids not only from low quality foods, but from the whole range of forages eaten by animals of this size. Neither of the current nutritional models, nor refinements of them satisfactorily explain the preponderance of the bovids among medium-sized ungulates; alternative hypotheses are presented.     

哺乳动物的消化策略（英文）

理解动物的营养生态位是充分理解其整个生态学的基础,对于害兽控制和物种保护也很重要,食肉动物的小肠很发达,这可能与对食物的高消化能力有关;杂食性动物有更复杂的胃肠器官,其后端有可进行发酵的盲肠,消化物的平均滞留时间（mean retention times,MRTs)更长;最长的平均滞留时间见于食草动物,其消化道内高密度的微生物种群对不同滞留区内的消化物进行发酵,但是,并不是所有的食草动物都能够最大程度地消化植物纤维,只有反刍动物、骆驼和个体较大的后肠发酵动物（hindgut fermenter)能够具有这种能力,对比而言,许多其它的食草动物,如前肠发酵的有袋类和小型的后肠发酵动物如兔子、田鼠和负鼠等,它们具备可以使植物纤维消化效率最大的消化系统,可以在食物中的纤维素含量非常高的情况下仍能处理大量的食物。这些不同的消化策略使哺乳动物具有广幅的营养生态位。     

The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut,and adaptations of hindgut fermenters

An oft-cited nutritional advantage of large body size is that larger animals have lower relative energy requirements and that, due to their increased gastrointestinal tract (GIT) capacity, they achieve longer ingesta passage rates, which allows them to use forage of lower quality. However, the fermentation of plant material cannot be optimized endlessly; there is a time when plant fibre is totally fermented, and another when energy losses due to methanogenic bacteria become punitive. Therefore, very large herbivores would need to evolve adaptations for a comparative acceleration of ingesta passage. To our knowledge, this phenomenon has not been emphasized in the literature to date. We propose that, among the extant herbivores, elephants, with their comparatively fast passage rate and low digestibility coefficients, are indicators of a trend that allowed even larger hindgut fermenting mammals to exist. The limited existing anatomical data on large hindgut fermenters suggests that both a relative shortening of the GIT, an increase in GIT diameter, and a reduced caecum might contribute to relatively faster ingesta passage; however, more anatomical data is needed to verify these hypotheses. The digestive physiology of large foregut fermenters presents a unique problem: ruminant-and nonruminant-forestomachs were designed to delay ingesta passage, and they limit food intake as a side effect. Therefore, with increasing body size and increasing absolute energy requirements, their relative capacity has to increase in order to compensate for this intake limitation. It seems that the foregut fermenting ungulates did not evolve species in which the intake-limiting effect of the foregut could be reduced, e.g. by special bypass structures, and hence this digestive model imposed an intrinsic body size limit. This limit will be lower the more the natural diet enhances the ingesta retention and hence the intake-limiting effect. Therefore, due to the mechanical characteristics of grass, grazing ruminants cannot become as big as the largest browsing ruminant. Ruminants are not absent from the very large body size classes because their digestive physiology offers no particular advantage, but because their digestive physiology itself intrinsically imposes a body size limit. We suggest that the decreasing ability for colonic water absorption in large grazing ruminants and the largest extant foregut fermenter, the hippopotamus, are an indication of this limit, and are the outcome of the competition of organs for the available space within the abdominal cavity. Our hypotheses are supported by the fossil record on extinct ruminant/tylopod species which did not, with the possible exception of the Sivatheriinae, surpass extant species in maximum body size. In contrast to foregut fermentation, the GIT design of hindgut fermenters allows adaptations for relative passage acceleration, which explains why very large extinct mammalian herbivores are thought to have been hindgut fermenters.     

A case of non-scaling in mammalian physiology? Body size, digestive capacity, food intake, and ingesta passage in mammalian herbivores

As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM(0.75)), it has been proposed that ingesta mean retention time (MRT) should scale to BM(0.25) in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n=74 species for gut capacity, n=93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM(1.06). In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM(0.76) across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM(0.14) across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM(0.04) in colon fermenters, BM(0.08) in non-ruminant foregut fermenters, BM(0.06) in browsing and BM(0.04) in grazing ruminants. In contrast, MRT significantly scaled to BM(0.24) (CI 0.16-0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg(0.75)) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants.     

The influence of natural diet composition, food intake level, and body size on ingesta passage in primates

An important component of digestive physiology involves ingesta mean retention time (MRT), which describes the time available for digestion. At least three different variables have been proposed to influence MRT in herbivorous mammals: body mass, diet type, and food intake (dry matter intake, DMI). To investigate which of these parameters influences MRT in primates, we collated data for 19 species from trials where both MRT and DMI were measured in captivity, and acquired data on the composition of the natural diet from the literature. We ran comparative tests using both raw species values and phylogenetically independent contrasts. MRT was not significantly associated with body mass, but there was a significant correlation between MRT and relative DMI (rDMI, g/kg(0.75)/d). MRT was also significantly correlated with diet type indices. Thus, both rDMI and diet type were better predictors of MRT than body mass. The rDMI-MRT relationship suggests that primate digestive differentiation occurs along a continuum between an "efficiency" (low intake, long MRT, high fiber digestibility) and an "intake" (high intake, short MRT, low fiber digestibility) strategy. Whereas simple-stomached (hindgut fermenting) species can be found along the whole continuum, foregut fermenters appear limited to the "efficiency" approach.     

Comparative chewing efficiency in mammalian herbivores

Although the relevance of particle size reduction in herbivore digestion is widely appreciated, few studies have investigated digesta particle size across species in relation to body mass or digestive strategy. We investigated faecal particle size, which reflects the size of ingesta particles after both mastication and specialized processes such as rumination. Particle size was measured by wet sieving samples from more than 700 captive individuals representing 193 mammalian species. Using phylogenetic generalized least squares, faecal particle size scaled to body mass with an exponent of 0.22 (95% confidence interval: 0.16–0.28). In comparisons among different digestive strategies, we found that (1) equids had smaller faecal particles than other hindgut fermenters, (2) non-ruminant foregut fermenters and hindgut fermenters had similar-sized faecal particles (not significantly different), and (3) ruminants had finer faecal particles than non-ruminants. These results confirm that the relationship between chewing efficiency and body mass is modified by morphological adaptations in dental design and physiological adaptations to chewing, such as rumination. This allometric relationship should be considered when investigating the effect of body size on digestive physiology, and digestion studies should include a measure of faecal particle size.     

Assessing the Jarman–Bell Principle: Scaling of intake,digestibility, retention time and gut fill with body mass in mammalian herbivores

Differences in allometric scaling of physiological characters have the appeal to explain species diversification and niche differentiation along a body mass (BM) gradient — because they lead to different combinations of physiological properties, and thus may facilitate different adaptive strategies. An important argument in physiological ecology is built on the allometries of gut fill (assumed to scale to BM^1.0) and energy requirements/intake (assumed to scale to BM^0.75) in mammalian herbivores. From the difference in exponents, it has been postulated that the mean retention time (MRT) of digesta should scale to BM^1.0–0.75 = BM^0.25. This has been used to argue that larger animals have an advantage in digestive efficiency and hence can tolerate lower-quality diets. However, empirical data does not support the BM^0.25 scaling of MRT, and the deduction of MRT scaling implies, according to physical principles, no scaling of digestibility; basing assumptions on digestive efficiency on the thus-derived MRT scaling amounts to circular reasoning. An alternative explanation considers a higher scaling exponent for food intake than for metabolism, allowing larger animals to eat more of a lower quality food without having to increase digestive efficiency; to date, this concept has only been explored in ruminants. Here, using data for 77 species in which intake, digestibility and MRT were measured (allowing the calculation of the dry matter gut contents (DMC)), we show that the unexpected shallow scaling of MRT is common in herbivores and may result from deviations of other scaling exponents from expectations. Notably, DMC have a lower scaling exponent than 1.0, and the 95% confidence intervals of the scaling exponents for intake and DMC generally overlap. Differences in the scaling of wet gut contents and dry matter gut contents confirm a previous finding that the dry matter concentration of gut contents decreases with body mass, possibly compensating for the less favorable volume–surface ratio in the guts of larger organisms. These findings suggest that traditional explanations for herbivore niche differentiation along a BM gradient should not be based on allometries of digestive physiology. In contrast, they support the recent interpretation that larger species can tolerate lower-quality diets because their intake has a higher allometric scaling than their basal metabolism, allowing them to eat relatively more of a lower quality food without having to increase digestive efficiency.     

Fibrobacter communities in the gastrointestinal tracts of diverse hindgut‐fermenting herbivores are distinct from those of the rumen

The genus Fibrobacter contains cellulolytic bacteria originally isolated from the rumen. Culture‐independent investigations have since identified Fibrobacter populations in the gastrointestinal tracts of numerous hindgut‐fermenting herbivores, but their physiology is poorly characterized due to few representative axenic cultures. To test the hypothesis that novel Fibrobacter diversity exists in hindgut fermenters, we performed culturing and 16S rRNA gene amplicon sequencing on samples collected from phylogenetically diverse herbivorous hosts. Using a unique approach for recovering axenic Fibrobacter cultures, we isolated 45 novel strains from 11 different hosts. Full‐length 16S rRNA gene sequencing of these isolates identified nine discrete phylotypes (cutoff = 0.03%) among them, including several that were only isolated from hindgut‐fermenting hosts, and four previously unrepresented by axenic cultures. Our phylogenetic analysis indicated that six of the phylotypes are more closely related to previously described subspecies of Fibrobacter succinogenes, while the remaining three were more closely related to F. intestinalis. Culture‐independent bacterial community profiling confirmed that most isolates were representative of numerically dominant phylotypes in their respective samples and strengthened the association of certain phylotypes with either ruminants or hindgut‐fermenters. Despite considerable phylogenetic diversity observed among the Fibrobacter strains isolated here, phenotypic characterization suggests a conserved specialization for growth on cellulose.     

Fibre digestibility in large herbivores as related to digestion type and body mass — An in vitro approach

The coexistence of different ungulate species in a given ecosystem has been the focus of many studies. Differences between ruminant foregut fermenters and hindgut fermenters were remarkable for example in the way they ingest and digest high fibre diets. Digestion trials based on total collections are difficult to conduct or are sometimes even not possible for wild animals in the field or in zoos. To gain information on the fibre digestion achieved by these animals and the influence of body mass (BM) thereon, a method using spot sampling is desirable. In this study, in vitro fermentation of faecal neutral detergent fibre (NDF) was used as a measure of fibre digestion in large ungulates. Food and faecal samples of 10 ruminant foregut fermenting and 7 hindgut fermenting species/breeds were collected. All animals received 100% grass hay with ad libitum access. The NDF of food and faeces was fermented in vitro in a Hohenheim gas test (HGT) for 96 h. The digestion type generally had an effect on the gas production (GP) of faecal NDF in the HGT with hindgut fermenters showing higher values than ruminant foregut fermenters. At any time interval of incubation, BM had no influence on GP. The results are in accordance with both findings that ruminant foregut fermenters have longer mean retention times and more comprehensive particle reduction and findings of a lack of influence of BM on digesta mean retention time. It can be stated that the HGT (96 h) is a useful and quick method to show also small differences within groups in fibre digestion.     

The relationship between forage cell wall content and voluntary food intake in mammalian herbivores

• 1 It is generally assumed that animals compensate for a declining diet quality with increasing food intake. Differences in the response to decreasing forage quality in herbivores have been postulated particularly between cattle (ruminants) and horses (hindgut fermenters). However, empirical tests for both assumptions in herbivorous mammals are rare.
• 2 We collected data on voluntary food intake in mammals on forage‐only diets and related this to dietary neutral detergent fibre (NDF) content, assuming a nonlinear correlation between these measurements. Generally, the paucity of corresponding data is striking.
• 3 Elephants and pandas showed very high food intakes that appeared unrelated to dietary fibre content. Only in small rodents, and possibly in rabbits, was an increase in food intake on forages of higher NDF content evident. In particular, other large herbivores, including horses, followed patterns of decreasing intake with increasing forage NDF, also observed in domestic cattle or sheep.
• 4 For large herbivores, empirical data therefore do not – so far – support the notion that intake is increased in response to declining diet quality. However, data are in accord with the assumption that most large herbivores have an anticipatory strategy of acquiring body reserves when high‐quality forage is available, and reducing food intake (and potentially metabolic losses) when only low‐quality forage is available.
• 5 Intake studies in which the influence of digestive strategy on food intake capacity is tested should be designed as long‐term studies that outlast an anticipatory strategy and force animals to ingest as much as possible.
• 6 We suggest that a colonic separation mechanism coupled with coprophagy, in order to minimize metabolic faecal losses, is necessary below a body size threshold where an anticipatory strategy (living off body reserves, migration) is not feasible. Future studies aimed at investigating fine‐scale differences, for example between equids and bovids, should focus on non‐domesticated species.

     

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.     

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.     

Phylogenetic constraints on digesta separation: Variation in fluid throughput in the digestive tract in mammalian herbivores

The relevance of the mean retention time (MRT) of particles through the gastrointestinal tract (GIT) is well understood and MRT(particle)GIT is an important parameter in digestion models. Solute markers have been used to estimate MRT(solute)GIT (or 'fluid passage') in animals, but the relevance of this measure is less evident and is usually sought in its relation to MRT(particle)GIT. The ratio between the two measures indicates the degree of 'digesta washing', with little washing occurring at ratios of 1, aborad washing at ratios >1 (where the solute marker travels faster than the particle marker), and orad (retrograde) washing at ratios <1 (where the solute marker travels slower than the particle marker). We analysed digesta washing in a dataset of 98 mammalian species including man of different digestion types (caecum, colon and nonruminant foregut fermenters, and ruminants), controlling for phylogeny; a subset of 72 species allowed testing for the influence of food intake level. The results indicate that MRT(solute)GIT and the degree of digesta washing are related to digestion type, whereas variation in MRT(particle)GIT is influenced mainly by effects of body mass and food intake. Thus, fluid throughput and digesta washing emerge as important correlates of digestive anatomy. Most importantly, primates appear constrained to little digesta washing compared to non-primate mammalian herbivores, regardless of their digestion type. These results may help explain the absence of primates from certain herbivore niches and represent a drastic example of a physiologic limitation in a phylogenetic group. More experimental research is required to illuminate relative benefits and costs of digesta washing.     

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.     

Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system

Summary A review is made of the ruminant digestive system in its morphophysiological variations and adaptations relating to foraging behaviour, digestive physiology, to interactions between plants and ruminants and to geographic and climatic diversity of ruminants' ecological niches. Evidence is provided for evolutionary trends from an extreme selectivity mainly for plant cell contents and dependence upon a fractionated fore- and hindgut fermentation, to an unselective intake of bulk roughage subjected to an efficient plant cell wall fermentation, mainly in the forestomachs. The review is based on detailed comparative morphological studies of all portions of the digestive system of 65 ruminant species from four continents. Their results are related to physiological evidence and to the classification of all extant ruminants into a flexible system of three overlapping morphophysiological feeding types: concentrate selectors (40%), grass and roughage eaters (25%) and intermediate, opportunistic, mixed feeders (35%). Several examples are discussed how ruminants of different feeding types are gaining ecological advantage and it is concluded that ruminants have achieved high levels of digestive efficiency at each evolutionary stage, (including well-documented seasonal adaptations of the digestive system) and that ruminant evolution is still going on. Deductions made from the few domesticated ruminant species may have, in the past, biased scientific evaluation of the free-ranging species' ecology. The main threat to a continuous ruminant evolution and diversity appears to be man's neglect for essential ecological interactions between wild ruminants and their specific habitats, which he alters or destroys.Abbreviations bw body weight - CS concentrate selector - DFC distal fermentation chamber (distended caecocolon) - GR grass and roughage eater - IM intermediate (mixed) feeder - PFC proximal fermentation chamber (ruminoreticulum/forestomachs) - RR Ruminoreticulum - SCFA Short-chain fatty acis (acetic, butyric, propionic acid set free by rumen bacteriae) - SE Surface enlargement (of absorptive mucosa) Supported by German Research Community grant DFG Ho 273/6Dedicated to Professor Dr. Dr. h.c. Dietrich Starck on the occasion of his 80th birthday     

Allocation of Matter in the Body of Growing Toads,Bufo bufo: Components of ‘Condition’

The condition, CI = [body mass (g)/length (cm)³]-1000, tends to increase in toads growing in the laboratory on a diet of meal-worms. The allocation was therefore studied of ingested food to growth corresponding to maintenance of standard condition (ΔW_S) and to increases in condition, expressing bulky growth. A condition index of 100, typical of toad populations, is chosen to characterize standard growth, higher values expressing bulky growth. The relationship between mass specific standard growth (ΔW_s/W₀) and actual growth in mass (ΔW/W₀) was the same in controls and growth hormone-treated toads and was independent of sex and season. It could be described by the allometric equation ΔW_s/W₀ = 0.28 (ΔW/W₀)^1.36, r = 0.93. The composition of mass representing increases in bulk in excess of a CI = 100 was assessed from allometric relationships established between the indices of the chemical constituents and the overall condition index. The increases in condition were partitioned among the organs and parts of the body from allometric relationships established between indices of organs and body parts and the overall condition index. Treatment with growth hormone enhanced growth in mass and significantly increased the relative proportion of mass allocated to standard growth. However, the effect was not specific to growth hormone, but was an indirect effect of the increased growth rate. Water was the predominant constituent of the growth in bulk, amounting to about 70% of increases in CI. Fat and protein contributed about equally initially, 5–10%, with fat strongly increasing and protein slightly decreasing with increasing condition, fat to approach 20–30% when CI approached 200. Increases in water content largely reflected increases in volume of blood and lymph.     

Digestive physiology of wild capybara

The capybara (Hydrochaeris hydrochaeris) is a hindgut fermenter whose digestive efficiency is comparable to that of ruminants on similar diets. It is an interesting case for study because it is the largest caecum fermenter and uses coprophagy as part of its digestive strategy. It practices coprophagy in the early morning and forages and defaecates in the evening. Its anatomy is well known but the limited information available about its digestive physiology has been obtained from captive animals. In this work we studied the capybara's digestive physiology, using microbial and chemical information from samples taken from wild capybaras in the early wet season in the morning (0600–0700 hours), noon (1200–1300 hours) and evening (1800–1900 hours), key points in the digestive cycle. Bacteria (cellulolytic and non-cellulolytic) and protozoa were present in high concentrations in the caecum and colon. There were no significant differences in nitrogen concentrations between digestive tract compartments in the coprophagy period (0600 hours), but in the other two periods nitrogen concentrations were significantly higher in the caecum than in the stomach and colon. This is suggestive of selective retention of microbial cells with fluid digesta in the caecum and of cecotrophy (the production of two distinctly different kinds of faeces — one kind called cecotrophes formed from caecal contents and ingested). The capybara hindgut (caecum and colon) with its content, was heavier during the dry season (period of poor diet quality) than in the wet season, but there were no significant seasonal differences between the stomach or small intestine and their contents. This suggests changes in the capacity of the hindgut, the site of microbial fermentation, related to seasonal variation in resource quality.Abbreviations NDF neutral-detergent fibre - SCFA Short-chain fatty acid(s)