Gross intestinal morphometry and allometry in ruminants

Targeted Screening of Fiber Degrading Bacteria with Probiotic Function in Herbivore Feces

Cellulolytic bacteria with probiotic functions play a crucial role in promoting the intestinal health in herbivores. In this study, we aimed to correlate the 16S rRNA gene amplicon sequencing and fiber-degrading enzyme activity data from six different herbivore feces samples. By utilizing the separation and screening steps of probiotics, we targeted and screened high-efficiency fiber-degrading bacteria with probiotic functions. The animals included Maiwa Yak (MY), Holstein cow (CC), Tibetan sheep (TS), Southern Sichuan black goat (SG), Sichuan white rex rabbit (CR), and New Zealand white rabbit (ZR). The results showed that the enzymes associated with fiber degradation were higher in goat and sheep feces compared to cattle and rabbit's feces. Correlation analysis revealed that Bacillus and Fibrobacter were positively correlated with five types of fiber-degrading related enzymes. Notably, the relative abundance of Bacillus in the feces of Tibetan sheep was significantly higher than that of other five herbivores. A strain TS5 with good cellulose decomposition ability from the feces of Tibetan sheep by Congored staining, filter paper decomposition test, and enzyme activity determination was isolated. The strain was identified as Bacillus velezensis by biological characteristics, biochemical analysis, and 16S rRNA gene sequencing. To test the probiotic properties of Bacillus velezensis TS5, we evaluated its tolerance to acid and bile salt, production of digestive enzymes, antioxidants, antibacterial activity, and adhesion ability. The results showed that the strain had good tolerance to pH 2.0 and 0.3% bile salts, as well as good potential to produce cellulase, protease, amylase, and lipase. This strain also had good antioxidant capacity and the ability to antagonistic Staphylococcus aureus BJ216, Salmonella SC06, Enterotoxigenic Escherichia coli CVCC196, and Escherichia coli ATCC25922. More importantly, the strain had good self-aggregation and Caco-2 cell adhesion rate. In addition, we tested the safety of Bacillus velezensis TS5 by hemolysis test, antimicrobial susceptibility test, and acute toxicity test in mice. The results showed that the strain had no hemolytic phenotype, did not develop resistance to 19 commonly used antibiotics, had no cytotoxicity to Caco-2, and did not have acute toxic harm to mice. In summary, this study targeted isolated and screened a strain of Bacillus velezensis TS5 with high fiber-degrading ability and probiotic potency. This strain can be used as a potential probiotic for feeding microbial preparations for ruminants.

Comparative gastrointestinal organ lengths among Amazonian primates (Primates: Platyrrhini)

OBJECTIVES

The morphological features of the gastrointestinal tract (GIT) in mammals reflect a species' food niche breadth and dietary adaptations. For many wild mammals, the relationship between the structure of the GIT and diet is still poorly understood, for example, the GIT for frugivorous primates is usually classified as unspecialized and homogeneous. Here, we compare the GIT structure of 13 primate species from the three families of extant platyrrhines (Atelidae, Pitheciidae, and Cebidae) in Amazonia, and discuss possible evolutionary adaptations to different diets and trophic niches.

METHODS

We measured the length of the esophagus, stomach, small intestine, large intestine, cecum, colon, and rectum of the digestive tracts of 289 primate specimens. We determined the allometric relationships of the different tubular organs with the total length of the GIT as a proxy of specimen body size. Allometric parameters were used to establish the quotients of differentiation of every organ for each primate specimen.

RESULTS

There was a high differentiation in structure of the digestive organs among genera. Alouatta specimens clearly separated from the other genera based on dissimilarities in gastric, colonic, and rectal quotients, likely linked to the fermentation of plant contents. In contrast, all cebines (Sapajus, Cebus, and Saimiri) and Cacajao species had similar small intestine quotients, which is expected due to their high rates of animal matter consumed.

CONCLUSIONS

We show that diverse adaptations in digestive structure exist among frugivorous primates, which in turn reflect different dietary patterns within this group that may enable the geographic coexistence of different primate species.

The Effect of Sexes and Seasons on the Morphological Structures of the Ruminant Digestive System of Blue Sheep (Pseudois nayaur)

Constant adaptation to environmental changes is required by ruminants to allow them to adapt to different ecological niches and feeding habits. In addition, the morphology and function of ruminant digestive systems reveal some adaptive evolutionary characteristics. Blue sheep (Pseudois nayaur) display a variety of morpho-physiological adaptations that are typical of grazers. In this study, we collected 64 adult blue sheep samples (whole animal carcasses) from the Helan Mountains, China, during different seasons. The external morphological parameters, digestive system morphological indexes, and rumen surface enlargement factors were determined. Our results reveal that the rumen and reticulum weights were positively correlated with the body weight (p = 0.004), while the food channel aperture, intestinal length, and weight of the blue sheep digestive tract presented no significant differences between different seasons (p > 0.05) and sexes (p > 0.05). There were significant differences (p < 0.001) in the density, length, and width of mastoids, and the rumen surface enlargement factor was 2.85 ± 1.37, which is typical of roughage feeders. The nutritional and ecological characteristics of blue sheep represent obvious morphological and physiological adaptations to an herbivorous diet. Adopting a quick foraging strategy allows blue sheep to rapidly consume and excrete large amounts of feed, thus obtaining the required energy for their activities and facilitating better adaption to environmental changes.

SEASONAL FLUCTUATION OF FECAL CONSISTENCY IN ZOO-HOUSED MOOSE (ALCES ALCES)

Fecal consistency is routinely used as an indicator of gastrointestinal health and diet suitability in zoo animals. The underlying processes in ungulate fecal consistency are not often investigated. The authors assessed multiple factors on fecal consistency scores in six adult zoo moose (Alces alces) retrospectively for a 3-yr period. All animals were regularly tested for gastrointestinal parasites and received antiparasitics when noted. Neither the provision of dietary browse nor number of visitors had a significant effect. Seasonally varying intake of the staple pelleted diet was the main explanatory factor, with an additional effect from environmental temperature or season. Higher intakes and higher temperatures were linked to less well-formed feces. The authors hypothesize that during the summer hyperphagia to replete body reserves, the water re-absorption function of the large intestine apparently becomes overtaxed. Heat stress may have an additional, intake-independent effect. Although monitoring fecal consistency is a part of good health surveillance, physiologic seasonal effects, as reported here, need to be taken into consideration when interpreting the observations.

Increased intake of mono- and disaccharides by Reeves's muntjac (Muntiacus reevesi). Effect on gastrointestinal tract structure and function and blood parameters

The aim of this study was to determine the effect of an increased mono- and disaccharide (MD) intake on selected functions and structure of the gastrointestinal tract (GIT), and selected blood parameters in Reeves's muntjac (Muntiacus reevesi), a small browsing ruminant. Eighteen male muntjacs were fed diets consisting of lucerne (ad libitum), a high fibre pellet (100 g/day) and wheat bran (30 g/day) without (MD0) or with addition of 10 or 20 g of glucose, fructose and sucrose mixture/day (MD10 and MD20, respectively) for 14 days. MD dosages were set to increase intake of these saccharides by 25% and 50% relative to MD0, which resulted in a range of water-soluble carbohydrate content in the consumed dry matter from 7% to 12%. Compared to MD0 animals, MD20 animals had a lower dry matter intake, a higher MD concentrations in the reticulorumen (RR), abomasal and small intestinal digesta, higher ruminal butyrate concentration, higher SGLT1 expression in the epithelium of proximal jejunum, higher plasma glucose, lower RR tissue weight but greater caecal tissue weight (p ≤ 0.05), and had or tended to have shorter papillae and lower mucosa surface area in the Atrium ruminis (by 44%; p = 0.02 and p = 0.10, respectively); MD10 animals tended to have higher MD concentrations in the abomasal and small intestinal digesta (p ≤ 0.10), and a higher amylolytic activity (p = 0.02) as well as a tendency to lower xylanolytic activity in the RR digesta (p = 0.06). MD supplementation did not affect ruminal pH. In conclusion, low to moderate increase of MD intake increased MD concentrations in the RR, abomasal and intestinal digesta, and SGLT1 expression in intestinal epithelium, suggesting incomplete fermentation of those saccharides in the RR. MD supplementation dose-dependently affects structure of GIT in Reeves's muntjac.

Shorter Grazing Time and Supplementation Are Beneficial for Gastrointestinal Tract Development and Carcass Traits of Growing Lambs

The effects of restricted grazing durations on the gastrointestinal development and carcass quality of growing lambs are poorly understood. In this study, 32 lambs were randomly assigned to four groups (n = 8, body weight = 21.86 kg) corresponding to 2, 4, 8 and 12 h of grazing per day. When off-pasture, all lambs were housed and fed concentrate and hay. When the grazing time decreased from 12 h to 2 h, the abomasum weight and large intestine length decreased (p = 0.019; p = 0.069). Compared to lambs grazed for 12 h, animals grazed for 2−4 h had a greater villus height and villus-to-crypt ratio in the duodenum, jejunum and ileum segments (p < 0.05); the 2 h lambs had superior carcass quality and a smaller diameter and area of the gluteus medium muscle fibers (p < 0.05), with no significant change after 4 h of grazing. The results indicated that shorter grazing times and supplementation were beneficial for the gastrointestinal tract development and carcass quality of growing lambs. Therefore, a better grazing management approach in Inner Mongolia could be to restrict the grazing of lambs to 4 h per day instead of grazing for more extended periods.

Mammalian intestinal allometry, phylogeny, trophic level and climate

An often-stated ecomorphological assumption that has the status of 'textbook knowledge' is that the dimensions of the digestive tract correlate with diet, where herbivores-consuming diets of lower digestibility-have longer intestinal tracts than faunivores-consuming diets of higher digestibility. However, statistical approaches have so far failed to demonstrate this link. Here, we collated data on the length of intestinal sections and body mass of 519 mammal species, and test for various relationships with trophic, climatic and other biological characteristics. All models showed a strong phylogenetic signal. Scaling relationships with body mass showed positive allometry at exponents greater than 0.33, except for the caecum, which is particularly large in smaller species. Body mass was more tightly linked to small intestine than to large intestine length. Adding a diet proxy to the relationships increased model fit for all intestinal sections, except for the small intestine when accounting for phylogeny. Thus, the diet has a main effect on the components of the large intestine, with longer measures in herbivores. Additionally, measures of habitat aridity had a positive relationship with large intestine length. The small intestine was longer in species from colder habitats at higher latitudes, possibly facilitating the processing of peak intake rates during the growing season. This study corroborates intuitive expectations on digestive tract anatomy, while the dependence of significant results on large sample sizes and inclusion of specific taxonomic groups indicates that the relationships cannot be considered fixed biological laws.

Ontogenetic scaling of the gastrointestinal tract of a marsupial foregut fermenter, the western grey kangaroo Macropus fuliginosus melanops

As an animal grows, the relative sizes of their organs may grow proportionately or disproportionately, depending on ontogenetic changes in function. If organ growth is proportional (isometric), then the exponent of the scaling equation is 1.0. Relative decreases or increases in size result in exponents less than 1 (hypoallometric) or greater than 1 (hyperallometric). Thus, the empirical exponent can indicate potential changes in function. The entire gastrointestinal tract (GIT) of the foregut-fermenting western grey kangaroo Macropus fuliginosus melanops exhibited biphasic allometry across five orders of magnitude body mass (M_b; 52.0 g-70.5 kg). Prior to weaning at around 12 kg M_b, the entire empty GIT mass scaled with hyperallometry (M_b^1.13), shifting to hypoallometry (M_b^0.80) post-weaning. In addition, there were varying patterns of hyper-, hypo-, and isometric scaling for select GIT organs, with several displaying phase shifts associated with major life-history events, specifically around exit from the maternal pouch and around weaning. Mass of the kangaroo forestomach, the main fermentation site, scaled with hyperallometry (M_b^1.16) before the stage of increased vegetation intake, and possibly after this stage (M_b^1.12; P = 0.07), accompanied by a higher scaling factor (elevation of the curve) probably associated with more muscle for processing fibrous vegetation. The acid hindstomach mass showed hyperallometry (M_b^1.15) before weaning, but hypoallometry (M_b ^0.58) post-weaning, presumably associated with decreasing intake of milk. Small intestine mass and length each scaled isometrically throughout ontogeny, with no discernible breakpoints at any life-history stage. The caecum and colon mass were steeply hyperallometric early in-pouch life (M_b^1.59-1.66), when the young were ectothermic, hairless, and supported solely by milk. After around 295 g M_b, caecum mass remained hyperallometric (M_b^1.14), possibly supporting its early development as a nidus for microbial populations to provide for secondary fermentation in this organ after the young transition from milk to vegetation.

Intraspecific macroscopic digestive anatomy of ring-tailed lemurs (Lemur catta), including a comparison of frozen and formalin-stored specimens

Digestive tract measurements are often considered species specific, but little information exists on the degree to which they change during ontogeny within a species. Additionally, access to anatomical material from nondomestic species is often limited, with fixed tissues possibly representing the only available source, though the degree to which this material is representative in terms of dimensions and weight is debatable. In the present study, the macroscopic anatomy of the digestive tract (length of intestinal sections, and tissue weights of stomach and intestines) of 58 Lemur catta [ranging in age from 1 month (neonates) to 25 years], which had been stored frozen (n = 27) or fixed in formalin (n = 31), was quantified. Particular attention was paid to the caecum and the possible presence of an appendix. The intraspecific allometric scaling of body mass (BM)^{0.46[0.40;0.51]} for total intestine length and BM^{0.48[0.41;0.54]} for small intestine length was higher than the expected geometric scaling of BM^0.33, and similar to that reported in the literature for interspecific scaling. This difference in scaling is usually explained by the hypothesis that, to maintain optimal absorption, the diameter of the intestinal tube cannot increase geometrically. Therefore, geometric volume gain of increasing body mass is accommodated for by more-than-geometric length scaling. According to the literature, not all L. catta have an appendix. No appendix was found in the specimens in the present study. The proportions of length measurements did not change markedly during ontogeny, indicating that the proportions of the foetus are representative of those of the adult animal. By contrast, width and tissue-mass scaling of the caecum indicated disproportionate growth of this organ during ontogeny that was not reflected in its length. Compared to overall intraspecific variation, the method of storage (frozen vs. formalin) had no relevant impact on length or weight measurements.

The uneven weight distribution between predators and prey: Comparing gut fill between terrestrial herbivores and carnivores

The general observation that secondary consumers ingest highly digestible food and have simple short guts and small abdominal cavities intuitively results in the assumption that mammalian carnivores carry less digesta in their gut compared to herbivores. Due to logistic constraints, this assumption has not been tested quantitatively so far. In this contribution, we estimated the dry matter gut contents (DMC) for 25 species of the order Carnivora (including two strictly herbivorous ones, the giant and the red panda) using the physical 'Occupancy Principle', based on a literature data collection on dry matter intake (DMI), apparent dry matter digestibility (aD DM) and retention time (RT), and compared the results to an existing collection for herbivores. Scaling exponents with body mass (BM) for both carnivores and herbivores were in the same range with DMI ~ BM^0.75; aD DM ~ BM⁰; RT ~ BM^0.11 and DMC ~ BM^0.88. The trophic level (carnivore vs herbivore) significantly affected all digestive physiology parameters except for RT. Numerically, the carnivore DMI level reached 77%, the RT 32% and DMC only 29% of the corresponding herbivore values, whereas the herbivore aD DM only reached 82% of that of carnivores. Thus, we quantitatively show that carnivores carry less inert mass or gut content compared to herbivores, which putatively benefits them in predator-prey interactions and might have contributed to the evolution towards unguligradism in herbivores. As expected, the two panda species appeared as outliers in the dataset with low aD DM and RT for a herbivore but extremely high DMI values, resulting in DMC in the lower part of the herbivore range. Whereas the difference in DMI and DMC scaling in herbivores might allow larger herbivores to compensate for lower diet quality by ingesting more, this difference may allow larger carnivores not to go for less digestible prey parts, but mainly to increase meal intervals, i.e. not having to hunt on a daily basis.

Gross intestinal morphometry and allometry in primates

Although it is generally assumed that among mammals and within mammal groups, those species that rely on diets consisting of greater amounts of plant fiber have larger gastrointestinal tracts (GIT), statistical evidence for this simple claim is largely lacking. We compiled a dataset on the length of the small intestine, caecum, and colon in 42 strepsirrhine, platyrrhine, and catarrhine primate species, using specimens with known body mass (BM). We tested the scaling of intestine length with BM, and whether dietary proxies (percentage of leaves and a diet quality index) were significant covariates in these scaling relationships, using two sets of models: one that did not account for the phylogenetic structure of the data, and one that did. Intestine length mainly scaled geometrically at exponents that included 0.33 in the confidence interval; Strepsirrhini exhibited particularly long caeca, while those of Catarrhini were comparatively short. Diet proxies were only significant for the colon and the total large intestine (but not for the small intestine or the caecum), and only in conventional statistics (but not when accounting for phylogeny), indicating the pattern occurred across but not within clades. Compared to terrestrial Carnivora, primates have similar small intestine lengths, but longer large intestines. The data on intestine lengths presented here corroborate recent results on GIT complexity, suggesting that diet, as currently described, does not exhaustively explain GIT anatomy within primate clades.