Little differences in digestive efficiency for protein and fat in mammals of different trophic guilds and digestive strategies: data constraints or fundamental functional similarity?

Carnivores do not vary markedly in their digestive efficiency for protein and fat, but whether they resemble other trophic guilds (omnivores and herbivores) in this respect has not been evaluated. We collated data on apparent crude protein (CP) and crude fat (ether extracts, EE) digestibility in 157 mammal species, applying the Lucas principle of regressing digestible nutrient content against nutrient content, where the slope of the regression equation represents the true digestibility and the intercept the metabolic losses per unit dry matter intake. The data collection is marked by the evident uneven distribution of dietary nutrient contents across trophic guilds and differences in the nutrient range by which different species have been evaluated, making statistical interpretation difficult. Results indicate a lower true digestibility of CP in herbivores compared to carnivores, most likely due to a lower digestibility of fibre-bound protein in herbivore diets. Metabolic CP losses did not appear to differ between trophic guilds, but herbivores had higher metabolic EE losses, compatible with the hypothesis that a higher proportion of metabolic CP losses were bound in microbes that also contain lipids in herbivores. Among herbivores, no clear pattern was evident that would indicate a difference in metabolic losses associated with microbes between digestive strategies (coprophagy, foregut/hindgut fermentation). Foregut fermenters had a lower true EE digestibility, possibly linked to the hydrogenation of lipids in their forestomach prior to digestion. The results do not demonstrate clear differences in digestive efficiency and metabolic losses for protein and fat between mammalian trophic guilds and digestive strategies, leading to the hypothesis that the process of CP and EE digestion is not physiologically challenging and hence does not lead to a noticeable differentiation between species or species groups.

Dry matter and digesta particle size gradients along the goat digestive tract on grass and browse diets.

Physical properties of the digesta vary along the ruminant digestive tract. They also vary within the forestomach, leading to varying degrees of rumen contents stratification in 'moose-type' (browsing) and 'cattle-type' (intermediate and grazing) ruminants. We investigated the dry matter concentration (DM) and the mean digesta particle size (MPS) within the forestomach and along the digestive tract in 10 goats fed grass hay or dried browse after a standardized 12-h fast, euthanasia and freezing in the natural position. In all animals, irrespective of diet, DM showed a peak in the omasum and an increase from caecum via colon towards the faeces and a decrease in MPS between the reticulum and the omasum. Both patterns are typical for ruminants in general. In the forestomach, there was little systematic difference between more cranial and more caudal locations ('horizontal stratification'), with the possible exception of large particle segregation in the dorsal rumen blindsac on the grass diet. In contrast, the typical (vertical) contents stratification was evident for DM (with drier contents dorsally) and, to a lower degree, for MPS (with larger particles dorsally). Although evident in both groups, this stratification was more pronounced on the grass diet. The results support the interpretation that differences in rumen contents stratification between ruminants are mainly an effect of species-specific physiology, but can be enhanced due to the diet consumed.

Predator-prey interactions amongst Permo-Triassic terrestrial vertebrates as a deterministic factor influencing faunal collapse and turnover.

Unlike modern mammalian communities, terrestrial Paleozoic and Mesozoic vertebrate systems were characterized by carnivore faunas that were as diverse as their herbivore faunas. The comparatively narrow food base available to carnivores in these paleosystems raises the possibility that predator-prey interactions contributed to unstable ecosystems by driving populations to extinction. Here, we develop a model of predator-prey interactions based on diversity, abundance and body size patterns observed in the Permo-Triassic vertebrate fossil record of the Karoo Basin, South Africa. Our simulations reflect empirical evidence that despite relatively high carnivore: herbivore species ratios, herbivore abundances were sufficient for carnivores to maintain required intake levels through most of the Karoo sequence. However, high mortality rates amongst herbivore populations, even accounting for birth rates of different-sized species, are predicted for assemblages immediately preceding the end-Guadalupian and end-Permian mass extinctions, as well as in the Middle Triassic when archosaurs replaced therapsids as the dominant terrestrial fauna. These results suggest that high rates of herbivore mortality could have played an important role in biodiversity declines leading up to each of these turnover events. Such declines would have made the systems especially vulnerable to subsequent stochastic events and environmental perturbations, culminating in large-scale extinctions.

Tooth length and incisal wear and growth in guinea pigs (Cavia porcellus) fed diets of different abrasiveness.

Dental diseases are among the most important reasons for presenting guinea pigs (Cavia porcellus) and other rodents to veterinary clinics, but the aetiopathology of this disease complex is unclear. Clinicians tend to believe that the ever-growing teeth of rabbits and rodents have a constant growth that needs to be worn down by the mastication of an appropriate diet. In this study, we tested the effect of four different pelleted diets of increasing abrasiveness [due to both internal (phytoliths) and external abrasives (sand)] or whole grass hay fed for 2 weeks each in random order to 16 guinea pigs on incisor growth and wear, and tooth length of incisors and cheek teeth. There was a positive correlation between wear and growth of incisors. Tooth lengths depended both on internal and external abrasives, but only upper incisors were additionally affected by the feeding of whole hay. Diet effects were most prominent in anterior cheek teeth, in particular M1 and m1. Cheek tooth angle did not become shallower with decreasing diet abrasiveness, suggesting that a lack of dietary abrasiveness does not cause the typical 'bridge formation' of anterior cheek teeth frequently observed in guinea pigs. The findings suggest that other factors than diet abrasiveness, such as mineral imbalances and in particular hereditary malocclusion, are more likely causes for dental problems observed in this species.

The effect of very low food intake on digestive physiology and forage digestibility in horses.

Equid digestion is often conceptualized as a high-throughput/low-efficiency system, in particular compared with ruminants. It is commonly assumed that ruminants have an advantage when resources are limited; the effect of low food intake on digestive physiology of horses has, however, not been explored to our knowledge. We used four adult ponies [initial body mass (BM) 288 ± 65 kg] in two subsequent trials with grass hay-only diets [in dry matter (DM): hay1, mid-early cut, crude protein (CP) 10.5%, neutral detergent fibre (NDF) 67.6%; hay2, late cut, CP 5.8%, NDF 69.5%], each fed subsequently at four different dry matter intake (DMI) levels: ad libitum and at 75, 55 and 30 g/kg(0.75) /day. We particularly expected digesta mean retention times (MRT) to increase, and hence fibre digestibility to increase, with decreasing DMI. Ponies maintained BM on the first, but lost BM and body condition on DMI55 and DMI30. MRTs were negatively correlated to DMI and ranged (for particles <2 mm) from 23/31 h (hay1/2) on the ad libitum to 38/48 h on DMI30. Digestibilities of DM, nutrients and fibre components decreased from DMI75 to DMI30; apparent digestibilities of organic matter and NDF (hay1/2) dropped from 47/43% and 42/37%, respectively, on the ad libitum DMI to 35/35% and 30/28% on DMI30. Additional differences evident between the two hays included a higher estimated 'true' protein digestibility for hay1 and finer faecal particles on hay2; there were no differences in faecal particle size between intake levels. The results suggest that below a certain food intake threshold, the major digestive constraint is not fermentation time but nutrient supply to gut bacteria. The threshold for such an effect probably varies between feeds and might differ between ruminants and equids.

A long life among ruminants: giraffids and other special cases.

In order to investigate differences in the relative maximum longevity and other life history parameter between ruminant species, we collated data on mean body mass, maximum longevity, gestation period and newborn mass in wild ruminant and camelid species. Among ruminants, giraffids (giraffe Giraffa camelopardalis and okapi Okapia johnstoni) have particularly high longevities, long gestation periods, and low intrauterine growth rates. A particularly high absolute and relative longevity is also achieved by the anoa (Bubalus depressicornis), a member of the bovinae (cattle-type ruminants) and an insular dwarf (inhabiting the Indonesian island of Sulawesi). The fact that some (but not all) other small ruminants also achieve surprisingly high longevities leads to the hypothesis that extreme relative longevities in this group are an indication for secondary body size reduction.

Water intake in domestic rabbits (Oryctolagus cuniculus) from open dishes and nipple drinkers under different water and feeding regimes.

Rabbits (Oryctolagus cuniculus) are often presented suffering from urolithiasis. A high water intake is important in the prophylaxis of uroliths. We investigated the influence factors for water intake using 12 rabbits subjected to different feed and water regimes with practical relevance: Hay, fresh parsley, a seed mix and two different pelleted feed were offered in diverse combinations. Water was provided either by open dish or nipple drinker. Water was accessible ad libitum except for four treatments with 6 h or 12 h water access. Under the different feeding regimes, the drinker had no influence on water intake, but faecal dry matter content was significantly higher with nipple drinkers [60.0 ± 2.1 vs. 57.2 ± 2.1% of wet weight (mean ± 95% confidence interval), p = 0.003]. Dry food led to a higher drinking water intake but total water intake was still lower than with addition of 'fresh' food. With restricted water access, rabbits exhibited a significantly higher water intake with open dishes compared with nipple drinkers (54.9 ± 9.8 vs. 48.1 ± 8.2 g/kg(0.75) /day (mean ± 95% confidence interval), p = 0.04). High proportions of fresh parsley or hay in the diet enhanced total water intake and urine output, and led to lower urinary dry matter content and lower urinary calcium concentrations. Restricted access to drinkers led to a decreased total daily water intake and increased dry matter content of urine and faeces. For optimal water provision and urolith prophylaxis, we recommend a diet with a high 'fresh food' proportion as well as additionally hay ad libitum with free water access, offered in an open bowl.

Do "savanna" chimpanzees consume C4 resources?

Several stable carbon isotopic studies have shown that South African australopiths consumed significant quantities of C(4) resources (tropical grasses, sedges, or animals that eat those foods), but relatively little is known about the consumption of such resources by chimpanzees. Here, we present stable carbon isotopic data for 36 chimpanzee hair samples from Fongoli, one of the driest and most open areas inhabited by chimpanzees. These data suggest that the Fongoli chimpanzees consume little in the way of C(4) vegetation or animals that eat such vegetation, even though these resources are locally abundant and preferred fruits are more widely scattered than at most chimpanzee study sites. The homogeneity of the Fongoli results is especially striking and recalls the narrow isotopic distribution of stenotopic savanna mammals. This is in stark contrast to what has been observed for australopiths, which had highly variable diets and consumed about 35% C(4) vegetation on average. Carbon isotope data for modern and fossil Papio depict a dietarily variable genus with a tendency to consume C(4) vegetation. This trophic flexibility, or willingness to consume C(4) savanna resources, may make Papio a more profitable ecological analog for australopiths than chimpanzees.