Search

Dietary carbon is oxidized and exhaled as CO2, thus δ13Cbreath values can provide information on diet and substrate use for energy. However, physiological phenomena such as fat deposition and fasting can alter values of δ13Cbreath such that interpretation of source contributions may be unclear. Consequently, before application to free-ranging animals, inferences about feeding and nutritional states based on δ13Cbreath should be validated with controlled experiments using captive individuals. Here, we report δ13Cbreath values for 4 captive brown bears (Ursus arctos) under different conditions: the bears were 1st given a diet containing carbohydrate, lipid, and protein; they were then switched to a carbohydrate-free diet consisting of salmon and fish oil; and finally they were placed on a fast leading to winter hibernation. Following the switch to the carbohydrate-free diet, values of δ13Cbreath and δ13Cplasma suggested that although oxidation included a substantial portion of dietary proteins, die...

Previous studies have demonstrated the potential of carbon and nitrogen stable isotope analysis (SIA) of feces for use in understanding dietary components and sources. These studies suggest that SIA is useful because it is noninvasive and provides more recent dietary information integrated over a shorter time period than SIA of tissues. We sought to determine whether SIA could be employed in the analysis of feces of American black bears (Ursus americanus) in Utah. Using archived feces, we compared SIA with gross fecal analyses (GFA) to determine if a relationship existed. The percent volume of grass and pine nuts were the only significant indicators of the δ13C of feces. The amount of animal matter was the sole significant indicator of the δ15N value of feces. Although these measures were only weakly indicative (R2 ≤ 0.21), it is interesting that even in an environment that is isotopically homogenous, δ15N and δ13C provided information on the contribution of dietary components. The comparatively ...

Summary 1. Accurately predicting isotope ratio discrimination is central to using mixing models to estimate assimilated diets of wild animals. This process is complicated when omnivores consume mixed diets because their discrimination is unlikely to be the weighted average of the various dietary constituents as occurs in current models. 2. We sought a basic understanding of how protein quality and quantity determine Δ15N and Δ34S in mammals and birds. Dietary protein is the primary source of both elements in many plants and animals. Low protein quality and high protein content have the potential to increase Δ15N by increasing protein turnover. 3. Protein quality, defined as the relative amount of the most limiting amino acid, accounted for 87–90% of the variation in Δ15N when mammals and birds consumed plant matter and mixed diets of plants and animals with protein of intermediate quality and quantity. However, foods containing relatively large amounts of high quality protein (i.e. vertebrate flesh) and foods with exceptionally low quality protein (e.g. lentils, Lens culinaris) had disparate nitrogen discriminations relative to what would be predicted from protein quality alone. 4. Supplementation of plant and animal diets with nitrogen-free carbohydrates and fats to reduce protein quantity did not reduce Δ15N in three plant-based diets fed to laboratory rats, but reduced Δ15N in two of three meat diets with >50% protein. 5. Δ34S was weakly correlated with Δ15N (R2 = 0·48) but was highly correlated with dietary δ34S (R2 = 0·89). Because methionine, a sulphur amino acid, was the most limiting amino acid in all diets, sulphur should be highly conserved as indicated by the lack of any change in Δ34S when diets were supplemented with carbohydrates and fat to both provide additional energy and reduce protein content. 6. Predictive equations incorporating both protein quality and quantity accounted for 81% of the variation in Δ15N and offer the opportunity to create more realistic mixing models to accurately estimate assimilated diets for omnivores.

Accurately predicting isotopic discrimination is central to estimating assimilated diets of wild animals when using stable isotopes. Current mixing models assume that the stable N isotope ratio (delta(15)N) discrimination (Delta(15)N) for each food in a mixed diet is constant and independent of other foods being consumed. Thus, the discrimination value for the mixed diet is the combined, weighted average for each food when consumed as the sole diet. However, if protein quality is a major determinant of Delta(15)N, discrimination values for mixed diets may be higher or lower than the weighted average and will reflect the protein quality of the entire diet and not that of the individual foods. This potential difference occurs because the protein quality of a mixed diet depends on whether, and to what extent, the profiles and amounts of essential amino acids in the individual foods are complementary or non-complementary to each other in meeting the animal's requirement. We tested these ideas by determining the Delta(15)N of several common foods (corn, wheat, alfalfa, soybean, and fish meal) with known amino acid profiles when fed singly and in combination to laboratory rats. Discrimination values for the mixed diets often differed from the weighted averages for the individual foods and depended on the degree of complementation. Delta(15)N for mixed diets ranged from 1.1 per thousand lower than the weighted average for foods with complementary amino acid profiles to 0.4 per thousand higher for foods with non-complementary amino acid profiles. These differences led to underestimates as high as 44% and overestimates as high as 36% of the relative proportions of fish meal and soybean meal N, respectively, in the assimilated mixed diets. We conclude that using isotopes to estimate assimilated diets is more complex than often appreciated and will require developing more biologically based, time-sensitive models.

Energy maximization, time minimization, and linear programming models subject to various constraints have dominated foraging ecology ideas and methods for decades. However, animals must use very complex physiological processes and foraging decisions to ensure fitness that in many cases may not be adequately described by these approaches. An example of this problem occurs when brown bears, Ursus arctos, have access to both abundant salmon and fruit. Salmon are one of the most energy and nutrient dense foods available to bears. Fruits are often high in soluble carbohydrates, low to deficient in many required nutrients, and more difficult to efficiently exploit. Therefore, wild brown bears that fatten primarily on fruits without access to salmon are 50% smaller than salmon-feeding bears. Thus, we predicted based on a linear, energy-maximizing model without dietary interaction effects that wild brown bears with access to both abundant salmon and fruit would feed almost exclusively on salmon. However, wild adult females with or without accompanying offspring foraged three times longer per day on fruit than on salmon. Similarly, the relative dry matter intake of ad libitum apples and salmon by captive, adult brown bears averaged 76 ±5% fruit and 24±5% salmon. Captive brown bears consuming mixed diets with intermediate dietary protein levels had 60% lower maintenance energy costs, 37% to 139% higher efficiencies of mass gain, and 72% to 520% higher maximum rates of gain than when they consumed either salmon or fruit alone. These relationships were nonlinear functions of dietary protein content in which salmon and fruit provided complementary nutritional resources. Both wild and captive bears attempted to regulate total protein, energy, and carbohydrate intake within a multidimensional intake target that both maximized energy intake and mass gain.

The capability to understand the nutritional ecology of free-ranging bears has increased dramatically in the last 20 years. Advancements have occurred because (1) managers and biologists recognized the need to link habitat quality, productivity, and variability with bear movements, home ranges, and demographic parameters like reproductive output, survival, and population growth, and (2) several research teams are using new methods to build on the results of earlier field studies. Our ability to couple new field methods and empirical field research with controlled experiments using captive bears has been central to our increased understanding of bear nutrition. Newer methods include the use of stable isotopes to quantify assimilated diet and nutrient flows within ecosystems, bioelectrical impedance to measure body composition, and naturally occurring mercury to estimate fish intake. Controlled experiments using captive bears have been integral to developing methods, isolating specific variables by...

Objective—To evaluate cardiac function parameters in a group of active and hibernating grizzly bears. Design—Prospective study. Animals—6 subadult grizzly bears. Procedure—Indirect blood pressure, a 12-lead ECG, and a routine echocardiogram were obtained in each bear during the summer active phase and during hibernation. Results—All measurements of myocardial contractility were significantly lower in all bears during hibernation, compared with the active period. Mean rate of circumferential left ventricular shortening, percentage fractional shortening, and percentage left ventricular ejection fraction were significantly lower in bears during hibernation, compared with the active period. Certain indices of diastolic function appeared to indicate enhanced ventricular compliance during the hibernation period. Mean mitral inflow ratio and isovolumic relaxation time were greater during hibernation. Heart rate was significantly lower for hibernating bears, and mean cardiac index was lower but not significantly different from cardiac index during the active phase. Contrary to results obtained in hibernating rodent species, cardiac index was not significantly correlated with heart rate. Conclusions and Clinical Relevance—Cardiac function parameters in hibernating bears are opposite to the chronic bradycardic effects detected in nonhibernating species, likely because of intrinsic cardiac muscle adaptations during hibernation. Understanding mechanisms and responses of the myocardium during hibernation could yield insight into mechanisms of cardiac function regulation in various disease states in nonhibernating species. (J Am Vet Med Assoc 2003;223:1170–1175)

Whitebark pine (Pinus albicaulis) is a masting species that produces relatively large, fat- and protein-rich nuts that are consumed by grizzly bears (Ursus arctos horribilis). Trees produce abundant nut crops in some years and poor crops in other years. Grizzly bear survival in the Greater Yellowstone Ecosystem is strongly linked to variation in pine-nut availability. Because whitebark pine trees are infected with blister rust (Cronartium ribicola), an exotic fungus that has killed the species throughout much of its range in the northern Rocky Mountains, we used stable isotopes to quantify the importance of this food resource to Yellowstone grizzly bears while healthy populations of the trees still exist. Whitebark pine nuts have a sulfur-isotope signature (9.2 ± 1.3‰ (mean ± 1 SD)) that is distinctly different from those of all other grizzly bear foods (ranging from 1.9 ± 1.7‰ for all other plants to 3.1 ± 2.6‰ for ungulates). Feeding trials with captive grizzly bears were used to develop relationships between dietary sulfur-, carbon-, and nitrogen-isotope signatures and those of bear plasma. The sulfur and nitrogen relationships were used to estimate the importance of pine nuts to free-ranging grizzly bears from blood and hair samples collected between 1994 and 2001. During years of poor pine-nut availability, 72% of the bears made minimal use of pine nuts. During years of abundant cone availability, 8 ± 10% of the bears made minimal use of pine nuts, while 67 ± 19% derived over 51% of their assimilated sulfur and nitrogen (i.e., protein) from pine nuts. Pine nuts and meat are two critically important food resources for Yellowstone grizzly bears.

We examined the energy and protein requirements, and the fiber and protein digestive capacity, of a small African ruminant, the blue duiker ( Cephalophus monticola), by conducting a series of complete balance digestion trials with three captive male blue duikers feeding on fruits, leaves, forbs, grass, and pelleted diets ranging from 9.4% to 49% neutral detergent fiber (NDF), and 2.5% to 30% crude protein. The diets also varied in tannin levels. On these diets, for which indigestible acid detergent lignin (ADL) comprised 5‐20% of NDF, blue duikers digested NDF as well as did larger ruminants. With a metabolic fecal nitrogen (MFN) of 2.6 g N/kg dry matter consumed and endogenous urinary N (EUN) of 194 mg/kg 0.75 /d, the duikers required 643.3 mg N/kg 0.75 /d. Therefore, if food intake is unrestricted, duikers require a minimum protein content in their diet of about 4%. MFN and N requirements were lower than those of many other ruminants. The protein-precipitating capacity of tannins found in forages used in this study did not reduce the digestibility of the neutral detergent solubles (NDS) and NDF, but significantly reduced protein digestion. However, this reduction appears to be less than that experienced by larger ruminants. Small ruminants, such as the blue duiker, seem to be able to handle lower-quality diets than expected for their size. Zoo Biol 21:123‐134, 2002. © 2002 Wiley-Liss, Inc.

Pygmy rabbits (Brachylagus idahoensis) are one of only three vertebrates that subsist virtually exclusively on sagebrush (Artemisia spp.), which contains high levels of monoterpenes that can be toxic. We examined the mechanisms used by specialist pygmy rabbits to eliminate 1,8-cineole, a monoterpene of sagebrush, and compared them with those of cottontail rabbits (Sylvilagus nuttalli), a generalist herbivore. Rabbits were offered food pellets with increasing concentrations of cineole, and we measured voluntary intake and excretion of cineole metabolites in feces and urine. We expected pygmy rabbits to consume more, but excrete cineole more rapidly by using less-energetically expensive methods of detoxification than cottontails. Pygmy rabbits consumed 3–5 times more cineole than cottontails relative to their metabolic body mass, and excreted up to 2 times more cineole metabolites in their urine than did cottontails. Urinary metabolites excreted by pygmy rabbits were 20 % more highly-oxidized and 6 times less-conjugated than those of cottontails. Twenty percent of all cineole metabolites recovered from pygmy rabbits were in feces, whereas cottontails did not excrete fecal metabolites. When compared to other mammals that consume cineole, pygmy rabbits voluntarily consumed more, and excreted more cineole metabolites in feces, but they excreted less oxidized and more conjugated cineole metabolites in urine. Pygmy rabbits seem to have a greater capacity to minimize systemic exposure to cineole than do cottontails, and other cineole-consumers, by minimizing absorption and maximizing detoxification of ingested cineole. However, mechanisms that lower systemic exposure to cineole may come with a higher energetic cost in pygmy rabbits than in other mammalian herbivores.

Zoos often offer large bones or cuts of meat containing bone (bone cuts) to carnivores to provide oral stimulation and behavioral enrichment. Because of its abrasive action, the act of chewing on a bone can increase the oral health of large felids as well as provide an enriching activity. Unfortunately, because the quantity of edible tissue on the bones is usually unknown, when feeding these cuts one can easily miscalculate an animal's caloric and nutrient intake. To fully comprehend the contribution of bones as a dietary item as opposed to an enrichment item, we removed the soft tissue from a total of 70 samples, representing 14 types of bone cuts commonly used in managed carnivore feeding programs. Across types of cuts, soft tissue averaged 50% of wet weight, with pork knuckles averaging the lowest (23%) and horse shanks the greatest (74%) percent soft tissue. Zoo Biol 27:154-158, 2008. (c) 2008 Wiley-Liss, Inc.

We tested the competing hypotheses that (1) nitrogen discrimination in mammals and birds increases with dietary nitrogen concentration or decreasing C:N ratios and, therefore, discrimination will increase with trophic level as carnivores ingest more protein than herbivores and omnivores or (2) nitrogen discrimination increases as dietary protein quality decreases and, therefore, discrimination will decrease with trophic level as carnivores ingest higher quality protein than do herbivores. Discrimination factors were summarized for five major diet groupings and 21 different species of birds and mammals. Discrimination did not differ between mammals and birds and decreased as protein quality (expressed as biological value) increased with trophic level (i.e., herbivores to carnivores). Relationships between discrimination factors and dietary nitrogen concentration or C:N ratios were either the opposite of what was hypothesized or non-significant. Dietary protein quality accounted for 72% of the variation in discrimination factors across diet groupings. We concluded that protein quality established the baseline for discrimination between dietary groupings, while other variables, such as dietary protein intake relative to animal requirements, created within-group variation. We caution about the care needed in developing studies to understand variation in discrimination and subsequently applying those discrimination factors to estimate assimilated diets of wild animals.

North American porcupines (Erethizon dorsatum) subsist predominantly on low-protein, high-fiber, high-tannin diets. Therefore, we measured the porcupine's ability to digest dry matter, fiber, and protein by conducting digestion trials on eight natural forages and one pelleted ration varying in concentration of fiber, nitrogen, and tannins. On these diets, dry matter intake ranged from 5 to 234 g/kg(0.75)/d and dry matter digestibility ranged from 62% to 96%. Porcupines digested highly lignified fiber better than many large hindgut fermenters and ruminants. The porcupine's ability to digest fiber may be explained, in part, by their lengthy mean retention time of particles (38.43+/-0.56 h). True nitrogen digestibility was 92% for nontannin forages and pellets. Endogenous urinary nitrogen was 205 mg N/kg(0.75)/d, and metabolic fecal nitrogen was 2.8 g N/kg dry matter intake. Porcupines achieved nitrogen balance at relatively low levels of nitrogen intake (346 mg N/kg(0.75)/d). Tannins reduced the porcupines' ability to digest protein. However, the reduction in protein digestion was not predictable from the amount of bovine serum albumin precipitated. Like many herbivores, porcupines may ameliorate the effects of certain tannins in natural forages on protein digestibility through physiological and behavioral adaptations.