Convergent evolution in feeding types: salivary gland mass differences in wild ruminant species

Morphological adaptation of the tongue of okapi (Okapia johnstoni Artiodactyla, Giraffidae)-Anatomy, histology, and ultrastructure

The aim of this study was to describe the morphology of the tongue of the okapi, and to compare the results with other ruminants including browsers, intermediates and grazers. The material was collected post-mortem from two animals from a Zoological Garden. The structure of the okapi tongue, focusing of the shape of the tongue, lingual surface, its papillae and lingual glands, was examined using gross morphology, light and polarized microscopy, and by scanning electron microscopy. The okapi tongue was characterized by dark pigmentation on the lingual dorsum (except lingual torus) and on the whole ventral surface. Two types of filiform papillae were observed, with additional, even 6-8 projections at their base. The round fungiform papillae were present at a higher density, up to 16/cm2, on the ventro-lateral area of the lingual apex. Round and elongate vallate papillae were arranged in two parallel lines between the body and root of the tongue. Numerous taste buds were detected within the epithelium of their vallum, while fungiform papillae had sparse taste buds. A lack of foliate papillae was noted. Very small conical papillae, some lenticular in shape, were present on the lingual torus. Thick collagen type I fibers were dominant over collagen type III fibers in the connective tissue of the lingual papillae. The mucous acini units were dominant among lingual glands, indicating that the secretion of okapi lingual glands was mostly mucous. In many aspects, the tongue of okapi resembles the tongue of other ruminants. The specific lingual shape and lingual surface, together with the lingual glands, support the processing of plant food, such as young and soft leaves. Although okapi tongue is characterized by smaller conical papillae compared to other ruminants, its high number of vallate papillae is similar that found in other browsers, intermediate and grazers. Thus the number of gustatory papillae rather indicates that this feature is not related to the type of feeding.

Detection of Hypoglycin A and MCPrG Metabolites in the Milk and Urine of Pasture Dairy Cows after Intake of Sycamore Seedlings

Hypoglycin A (HGA), methylenecyclopropylglycine (MCPrG), hypoglycin B (HGB), and γ-glutamyl-α-(methylenecyclopropyl) glycine (γ-glutamyl-MCPrG) are secondary plant metabolites occurring in sycamore maple (Acer pseudoplatanus) as well as several other Sapindaceae (e.g., Blighia sapida). By interfering with energy metabolism, they may cause severe intoxication in humans and other species. However, to date, there is not enough data available concerning the intake, metabolism, or excretion of sycamore maple toxins in dairy cows. In May 2022, five cows were observed over four days, when they had first access to a pasture with two sycamore maples. Grazing of their seedlings that grew numerously in between the pasture plants was monitored by direct observation. Milk samples were drawn both from individual cows and from the bulk tank. Spontaneous urine samples were collected from all cows on day 3 after access to the pasture. Seedlings (100 g) were sampled on the pasture and analyzed, together with milk and urine samples, for sycamore toxins and their metabolites using liquid chromatography-tandem mass spectrometry and liquid chromatography-high-resolution mass spectrometry. Cows ingested sycamore seedlings while grazing. Values of HGA in milk were below the limit of quantification. However, metabolites of HGA and MCPrG were detected in individual milk samples already at the end of the first day of grazing. Urine samples of all five cows showed higher concentrations of conjugated HGA and MCPrG metabolites than in milk. Observations suggest that dairy cows may have a low susceptibility toward sycamore maple toxins. However, whether this could be attributed to foregut fermenting species in general requires further elucidation.

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

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

Coexistence mechanisms of sympatric ungulates: Behavioral and physiological adaptations of blue sheep (Pseudois nayaur) and red deer (Cervus elaphus alxaicus) in Helan Mountains, China

Studying the coexistence mechanisms of sympatric wildlife helps to shed light on why the earth has so many different species. When ungulates share ranges, food and habitat requirements may partially or fully overlap. Therefore, the aim of this study was to determine how sympatric ungulates share limited resources. Carcasses of 27 adult blue sheep (Pseudois nayaur) and three adult red deer (Cervus elaphus alxaicus) were collected in the Helan Mountains, China. Nutritive indices of plant species foraged and morphometric measurements of the digestive system of the two sympatric ungulates were determined. In addition, 120 passive, infrared motion-triggered cameras recorded spatial overlap and temporal overlap between the two species. Camera trapping revealed relatively limited spatial overlap and significantly different activity rhythms between blue sheep and red deer. Differences were also observed in stomach weight, surface enlargement factor of the rumen, and intestine length between the two species. However, the combined relative weight of the stomach and intestine was not different between species. The low spatiotemporal overlap decreased opportunities for encounters between sympatric blue sheep and red deer, and significant differences in digestive systems allowed the two species to consume different plant species or different parts of the same species. Thus, the two sympatric ungulates coexist harmoniously in the Helan Mountains because of long-term evolutionary behavioral and physiological adaptations that eliminate negative effects on the survival of the other species.

Acer pseudoplatanus: A Potential Risk of Poisoning for Several Herbivore Species

Acer pseudoplatanus is a worldwide-distributed tree which contains toxins, among them hypoglycin A (HGA). This toxin is known to be responsible for poisoning in various species, including humans, equids, Père David's deer and two-humped camels. We hypothesized that any herbivore pasturing with A. pseudoplatanus in their vicinity may be at risk for HGA poisoning. To test this hypothesis, we surveyed the HGA exposure from A. pseudoplatanus in species not yet described as being at risk. Animals in zoological parks were the major focus, as they are at high probability to be exposed to A. pseudoplatanus in enclosures. We also searched for a toxic metabolite of HGA (i.e., methylenecyclopropylacetyl-carnitine; MCPA-carnitine) in blood and an alteration of the acylcarnitines profile in HGA-positive animals to document the potential risk of declaring clinical signs. We describe for the first instance cases of HGA poisoning in Bovidae. Two gnus (Connochaetes taurinus taurinus) exposed to A. pseudoplatanus in their enclosure presented severe clinical signs, serum HGA and MCPA-carnitine and a marked modification of the acylcarnitines profile. In this study, even though all herbivores were exposed to A. pseudoplatanus, proximal fermenters species seemed less susceptible to HGA poisoning. Therefore, a ruminal transformation of HGA is hypothesized. Additionally, we suggest a gradual alteration of the fatty acid metabolism in case of HGA poisoning and thus the existence of subclinical cases.

A pilot study on dietary and faecal calcium/phosphorus ratios in different types of captive ruminating herbivores

Quantitative differences in calcium and phosphorus metabolism between domestic species exist and can be visualised using data on calcium and phosphorus intake and faecal excretion. The parameter for analysing the results was defined as Δ = dietary calcium/phosphorus (Ca/P) ratio – faecal Ca/P ratio. In previous studies, hindgut fermenters had significantly higher Δ values than ruminants (sheep, cattle, goats), which was explained by the high calcium digestibilities in hindgut fermenters in contrast to highly efficient phosphorus recycling in ruminants. The first hypothesis of the present study was that different types of ruminants (grazer, browser, intermediate feeder) would show differences in Δ as a proxy for quantitative calcium and phosphorus metabolism. The second hypothesis was that camelids as functional, but not taxonomic ruminants would show Δ values similar to ruminants. We used herbivorous zoo animals (17 species, hindgut and foregut fermenters), which were kept on their regular diet without variation for 1 week. Then, faecal samples were obtained from the individual animals. Feed items and faecal samples were analysed for calcium and phosphorus, and dietary and faecal Ca/P ratios as well as Δ were calculated. A comparison of the species groups (one‐way ANOVA on ranks, p < 0.05) showed that zoo hindgut fermenters had significantly higher Δ values (0.67 ± 0.34) than camelids and zoo ruminants (–1.07 ± 0.35 and –1.87 ± 1.56). There was no significant difference between camelids, grazers (–1.49 ± 1.31), browsers (–1.63 ± 0.88) and intermediate feeders (–2.11 ± 1.76). The ruminant species from this study had markedly lower Δ than domestic ruminants from literature data. Especially intermediate feeders had low Δ, possibly due to more efficient phosphorus recycling than the domestic ruminants.

Detailed gross anatomic and sialographic characteristics of major salivary glands in water buffaloes (Bubalus bubalis)

To clarify the detailed general architecture and topography of major salivary glands and demonstrate a fine anatomy of the ductal system of the glands in water buffaloes, we conducted gross anatomic and sialographic investigations of glands in 14 half heads from seven water buffaloes. The position of the mandibular gland, course of mandibular duct relative to monostomatic gland, a rostral extension of polystomatic gland, and site of origin of monostomatic duct in buffaloes essentially differed from those of various ruminants. The shape of the parotid and mandibular glands, and origin of their ducts, lacking filling of retromandibular fossa by parotid gland, the topography of mandibular gland relative to the parotid gland and mandibular lymph node, caudal extension of polystomatic gland, rostral extension of monostomatic gland, and location of polystomatic gland relative to monostomatic gland in buffaloes were very similar to those in ox. However, several considerable differences in morphology of glands in buffaloes and ox were recognized. Major salivary glands in buffaloes almost show 'grazing ruminants' morphological and morphometrical characteristics. Within parotid, mandibular, and monostomatic glands in buffaloes, there was a ductal arborization pattern in lateral sialograms. Whereas the main parotid duct was formed by a union of two central branches of the intraglandular duct, main mandibular, and monostomatic ducts were consisted of one central branch. The pattern of peripheral branches from the central branch of intraglandular duct in buffaloes was significantly different among the glands. Our detailed sialography of ductal morphology and morphometry can be helpful in accurate diagnosis of gland diseases in live water buffaloes.

Are there phylogenetic differences in salivary tannin-binding proteins between browsers and grazers, and ruminants and hindgut fermenters?

While feeding, mammalian browsers (primarily eat woody plants) encounter secondary metabolites such as tannins. Browsers may bind these tannins using salivary proteins, whereas mammalian grazers (primarily eat grasses that generally lack tannins) likely would not. Ruminant browsers rechew their food (ruminate) to increase the effectiveness of digestion, which may make them more effective at binding tannins than nonruminants. Few studies have included a sufficient number of species to consider possible scaling with body mass or phylogenetic effects on salivary proteins. Controlling for phylogeny, we ran inhibition radial diffusion assays of the saliva of 28 species of African herbivores that varied in size, feeding strategy, and digestive system. We could not detect the presence of salivary proline-rich proteins that bind tannins in any of these species. However, using the inhibition radial diffusion assay, we found considerable abilities to cope with tannins in all species, albeit to varying degrees. We found no differences between browsers and grazers in the effectiveness of their salivary proteins to bind to and precipitate tannins, nor between ruminants and nonruminants, or scaling with body mass. Three species bound all tannins, but their feeding niches included one browser (gray duiker), one mixed feeder (bush pig), and one grazer (red hartebeest). Five closely related species of small ruminant browsers were very effective in binding tannins. Megaherbivores, considered generalists on account of their large body size, were capable of binding tannins. However, the grazing white rhinoceros was almost as effective at binding tannins as the megaherbivore browsers. We conclude, contrary to earlier predictions, that there were no differences in the relative salivary tannin-binding capability that was related to common ancestry (phylogeny) or to differences in body size.

Digesta passage in common eland (Taurotragus oryx) on a monocot or a dicot diet

The way that fluids and particles move through the forestomach of a ruminant is species-specific, and can be used to classify ruminants according to their digestive physiology into 'moose-types' (with little difference in fluid and small particle passage) and 'cattle-types' (where fluids move through the forestomach much faster than small particles). So far, 'moose-types' appear limited to a dietary niche of browsing, whereas 'cattle-types' are particularly prominent in the intermediate and grazing diet niches. However, some species, including members of the spiral-horned antelopes (the Tragelaphini), have a 'cattle-type' physiology but a browse-dominated diet niche. Eland (Taurotragus oryx), the largest member of the Tragelaphini, are strict browsers in the wild but have been considered intermediate feeders in the past, and can seemingly be maintained on grass diets. We quantified food intake, mean retention time (MRT) in the gastrointestinal tract and the reticulorumen (RR) of a solute, a small and a large particle marker, and diet digestibility in six eland each fed a monocot (grass hay) and a dicot (lucerne silage) forage. Food intake and digestibility was lower on the diet with higher fibre content (grass hay), with corresponding longer MRT. At the higher intakes on lucerne, the difference in MRT between small and large particles was larger, indicating a greater reliance on particle sorting and clearance under this condition of potentially limiting gut capacity. Regardless of diet or intake, the ratio of small particle and solute MRT in the RR was constant and small, at a quotient of 1.54, classifying the eland as a typical 'moose-type' ruminant. This finding is consistent with previous literature reports on low faecal metabolic nitrogen and high apparent protein digestibility in eland. Given the relative ease at which eland can be maintained under farm husbandry conditions, they appear ideal model ruminants to study the effects of differences in rumen physiology compared to cattle.

Digesta passage in nondomestic ruminants: Separation mechanisms in 'moose-type' and 'cattle-type' species, and seemingly atypical browsers

Ruminants have been classified as having a 'moose-type' or 'cattle-type' digestive physiology. 'Cattle-type' ruminants have a clear difference in the mean retention time (MRT) of fluid vs. small particles in the reticulorumen (RR), with a high 'selectivity factor' (SF = MRT_particle/ MRT_fluid, >1.80), and are typically grazers and intermediate feeders. 'Moose-type' ruminants have lower SF (<1.80), possibly because of defensive salivary proteins that constrain amounts of (high-viscosity) saliva, and are typically restricted to browsing. To further contribute to testing this physiology-diet correlation, we performed 55 individual passage measurements in 4/6 species that have/have not been investigated previously, respectively. Co-EDTA was used as a solute (fluid) and Cr-mordanted hay particles (<2 mm) as particle markers. Results are related to the percentage of grass in the natural diet taken from the literature. Moose (Alces alces, n = 4 on 4 to 5 diets each and n = 2 on a single diet, 5% grass, SF 1.46 ± 0.22) and giraffe (Giraffa camelopardalis, n = 3 on 3 to 5 diets each, 1%, 1.42 ± 0.23) as classical 'moose-type', and cattle (Bos taurus, n = 2, 70%, 2.04) as classical 'cattle-type' ruminants yielded results similar to those previously published, as did waterbuck (Kobus ellipsiprymnus, n = 5, 84%, 2.46 ± 0.49), corroborating that the SF represents, to a large extent, a species-specific characteristic. Results in oryx (Oryx leucoryx, n = 1, 75%, 2.60) and sitatunga (Tragelaphus spekii, n = 4, 68%, 1.81 ± 0.21) correspond to the concept of 'cattle-type' ruminants being grazers or intermediate feeders. However, European bison (Bison bonasus, n = 1, 10%, 2.74), nyala (T. angasii, n = 6, 20%, 1.95 ± 0.25), bongo (T. eurycerus, n = 3, 13%, 2.39 ± 0.54) and gerenuk (Litocranius walleri, n = 1, 0%, 2.25) appear as 'cattle-type' ruminants, yet have a browse-dominated diet. While the results do not challenge the view that a 'moose-type' digestive physiology is an adaptation to browse diets, they indicate that it may not be the only adaptation that enables ruminants to use browse. Apparently, a 'cattle-type' digestive physiology with a high SF does not necessarily preclude a browsing diet niche. High-SF browsers might have the benefit of an increased harvest of RR microbiota and grit removal prior to rumination; how they defend themselves against secondary plant compounds in browse remains to be investigated.

An in vitro evaluation of browser and grazer fermentation efficiency and microbiota using European moose spring and summer foods

Evolutionary morphological and physiological differences between browsers and grazers contribute to species‐specific digestion efficiency of food resources. Rumen microbial community structure of browsers is supposedly adapted to characteristic nutrient composition of the diet source. If this assumption is correct, domesticated ruminants, or grazers, are poor model animals for assessing the nutritional value of food consumed by browsing game species. In this study, typical spring and summer foods of the European moose (Alces alces) were combined with rumen fluid collected from both dairy cows (Bos taurus) and from moose, with the aim of comparing fermentation efficiency and microbial community composition. The nutritional value of the food resources was characterized by chemical analysis and advanced in vitro measurements. The study also addressed whether or not feed evaluation based on in vitro techniques with cattle rumen fluid as inoculum could be a practical alternative when evaluating the nutritional value of plants consumed by wild browsers. Our results suggest that the fermentation characteristics of moose spring and summer food are partly host‐specific and related to the contribution of the bacterial phyla Firmicutes and Bacteriodetes to the rumen microbial community. Host‐specific adaptations of the ruminal microbial community structure could be explained from the evolutionary adaptations related to feeding habitats and morphophysiological differences between browsers and grazers. However, the observed overall differences in microbial community structure could not be related to ruminal digestion parameters measured in vitro. The in vitro evaluation of digestion efficiency reveals that equal amounts of methane were produced across all feed samples regardless of whether the ruminal fluid was from moose or dairy cow. The results of this study suggested that the nutritional value of browsers' spring and summer food can be predicted using rumen fluid from domesticated grazers as inoculum in in vitro assessments of extent of digestion when excluding samples of the white water lily root, but not of fermentation characteristics as indicated by the proportions of individual fermentation fatty acids to the total of volatile fatty acids.

Factors Affecting Leaf Selection by Foregut-fermenting Proboscis Monkeys: New Insight from in vitro Digestibility and Toughness of Leaves

Free-living animals must make dietary choices in terms of chemical and physical properties, depending on their digestive physiology and availability of food resources. Here we comprehensively evaluated the dietary choices of proboscis monkeys (Nasalis larvatus) consuming young leaves. We analysed the data for leaf toughness and digestibility measured by an in vitro gas production method, in addition to previously reported data on nutrient composition. Leaf toughness, in general, negatively correlated with the crude protein content, one of the most important nutritional factors affecting food selection by leaf-eating primates. This result suggests that leaf toughness assessed by oral sensation might be a proximate cue for its protein content. We confirmed the importance of the leaf chemical properties in terms of preference shown by N. larvatus; leaves with high protein content and low neutral detergent fibre levels were preferred to those of the common plant species. We also found that these preferred leaves were less tough and more digestible than the alternatives. Our in vitro results also suggested that N. larvatus were little affected by secondary plant compounds. However, the spatial distribution pattern of plant species was the strongest factor explaining the selection of the preferred leaf species.

Snout shape in extant ruminants

Snout shape is a prominent aspect of herbivore feeding ecology, interacting with both forage selectivity and intake rate. Previous investigations have suggested ruminant feeding styles can be discriminated via snout shape, with grazing and browsing species characterised by ‘blunt’ and ‘pointed’ snouts respectively, often with specification of an ‘intermediate’ sub-grouping to represent ambiguous feeding styles and/or morphologies. Snout shape morphology is analysed here using a geometric morphometric approach to compare the two-dimensional profiles of the premaxilla in ventral aspect for a large sample of modern ruminant species, for which feeding modes are known from secondary criteria. Results suggest that, when browsing and grazing ruminants are classified ecologically based on a range of feeding style indicators, they cannot be discriminated unambiguously on the basis of snout profile shape alone. Profile shapes in our sample form a continuum with substantial overlap between groupings and a diverse range of morphologies. Nevertheless, we obtained an 83.8 percent ratio of correct post hoc feeding style categorisations based on the proximity of projected profile shapes to group centroids in the discriminant space. Accordingly, this procedure for identifying species whose feeding strategy is ‘unknown’ can be used with a reasonable degree of confidence, especially if backed-up by additional information. Based on these results we also refine the definitions of snout shape varieties, taking advantage of the descriptive power that geometric morphometrics offers to characterize the morphological disparities observed. The shape variance exhibited by both browsing and grazing ruminants corresponds strongly to body mass, providing further evidence for an interaction between snout shape, feeding style, and body size evolution. Finally, by exploring the role of phylogenetic similarity in snout shape, we find a slight increase in successful categorisation when repeating the analysis with phylogenetic control on the geometric profiles.

Rumen physiology constrains diet niche: linking digestive physiology and food selection across wild ruminant species

We propose a hypothesis for digestive constraints on the browsing and grazing options available to ruminants: that the diet-niche range (maximum and minimum grass intake) of a species is dependent upon its predisposition to stratified rumen contents, based on observations that this characteristic is a critical step towards enhanced fibre digestion and greater fluid throughput. We compare a physiological (heterogeneity of ingesta fluid content) and an anatomical (the intraruminal papillation pattern) measure with dietary evidence for a range of African and temperate species. Both measures are strongly related to the mean percentage of grass in species’ natural diets, as well as to the maximum and minimum levels of grass intake, respectively. The nature of these effects implies a stratification-level threshold, below which a species will not use a grass-based diet, but above which grass consumption can increase exponentially. However, above this threshold, a minimum percentage of grass in the diet is a prerequisite for optimal performance. We argue that this second constraint is crucial, as it depicts how a greater fluid throughput reduces potential for detoxification of plant secondary compounds, and therefore limits the maximum amount of browse a stratifying species will consume.

Gross anatomy of the intestine in the giraffe (Giraffa camelopardalis)

We describe the macroscopic anatomy of the intestine of the giraffe (Giraffa camelopardalis). The small intestine was divided into duodenum, jejunum and ileum as usual. The caecum was attached to the ileum by a long ileocaecal fold, and to the proximal ansa of the ascending colon by a caecocolic fold. The ascending colon was the most developed portion of the gross intestine and had the most complex arrangement with three ansae: the proximal ansa, the spiral ansa and the distal ansa. The proximal ansa completely encircled the caecum, describing a 360 degrees gyrus, and represented the widest portion of the intestine. The spiral ansa was formed by three and a half centripetal gyri, a central flexure and three centrifugal gyri. The last centrifugal gyrus left the spiral and described nine flexures of different form and direction over the left side of the mesentery. The two portions that formed each of these flexures ran parallel to each other. The last part of this gyrus ran parallel to the jejunum. When compared with domestic cattle, giraffe had a comparatively short small intestine and a comparatively long large intestine, with a resulting small ratio of small:large intestine. Reasons are presented why this should be considered a peculiarity of cattle-like ruminants rather than a different representative of a browser-grazer dichotomy in general.