Summary 1.Nutrition influences most aspects of animal ecology: juvenile growth rates and adult mass gain, body condition, probability of pregnancy, over-winter survival, timing of parturition, and neonatal birth mass and survival. We provide an overview among ungulates of the extent of these influences resulting from interactions among bioenergetics, foraging, and nutritional demands. 2. Body condition of an animal is the integrator of nutritional intake and demands, affecting both survival and reproduction. The deposition and mobilization of body fat and body protein vary with physiological requirements and environmental conditions as species use dietary income and body stores to integrate the profits of summer and the demands of winter. Results from our simulation model and uncertainty analysis of the influence of body mass and changes in body composition of Rangifer over winter indicate that percent body fat rather than body mass in early winter is most important in determining whether animals die, live without reproducing, or live and reproduce. Animal responses are also sensitive to rates of change in body protein. Depending on timing of calving and maternal reserves, seasonal habitats vary in their nutritional value for the production of offspring. 3. For free-ranging animals, life is a balance among numerous ecological factors, including nutritional requirements, nutritional resources to meet those demands, and intra-and inter-specific interactions. Predation effects on population demography may mask nutritional limitations of habitat. We suggest that over the long term of life histories, ungulates use seasonal strategies that minimize the maximum detriment, and that the basis for most strategies is nutritional.

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BackgroundHerbivores rely on digestive tract lignocellulolytic microorganisms, including bacteria, fungi and protozoa, to derive energy and carbon from plant cell wall polysaccharides. Culture independent metagenomic studies have been used to reveal the genetic content of the bacterial species within gut microbiomes. However, the nature of the genes encoded by eukaryotic protozoa and fungi within these environments has not been explored using metagenomic or metatranscriptomic approaches.Methodology/Principal FindingsIn this study, a metatranscriptomic approach was used to investigate the functional diversity of the eukaryotic microorganisms within the rumen of muskoxen (Ovibos moschatus), with a focus on plant cell wall degrading enzymes. Polyadenylated RNA (mRNA) was sequenced on the Illumina Genome Analyzer II system and 2.8 gigabases of sequences were obtained and 59129 contigs assembled. Plant cell wall degrading enzyme modules including glycoside hydrolases, carbohydrate esterases and polysaccharide lyases were identified from over 2500 contigs. These included a number of glycoside hydrolase family 6 (GH6), GH48 and swollenin modules, which have rarely been described in previous gut metagenomic studies.Conclusions/SignificanceThe muskoxen rumen metatranscriptome demonstrates a much higher percentage of cellulase enzyme discovery and an 8.7x higher rate of total carbohydrate active enzyme discovery per gigabase of sequence than previous rumen metagenomes. This study provides a snapshot of eukaryotic gene expression in the muskoxen rumen, and identifies a number of candidate genes coding for potentially valuable lignocellulolytic enzymes.

We studied bred and unbred female reindeer (Rangifer tarandus tarandus) during 12 wk of winter when ambient temperatures were low and nitrogen (N) demand for fetal growth is highest in pregnant females. Animals were fed a complete pelleted diet ad lib. that contained 2.54% N in dry matter that was 80% +/- 2% (X +/- SD) digestible. Female reindeer lost 64% +/- 14% of body fat but gained 34% +/- 11% of lean mass from 10 wk prepartum to parturition. These changes were equivalent to average balances of -14.14 +/- 2.35 MJ d(-1) and 10 +/- 3 g N d(-1). Blood cells, serum, and urine declined in (15)N/(14)N in late winter as body protein was gained from the diet. Blood cells of newborn calves were more enriched in (15)N and (13)C than that of their mothers, indicating the deposition of fetal protein from maternal stores. To quantify pathways of N flow in reindeer, N balance was measured by confining animals to cages for 10 d at 4 wk from parturition. N balance was inversely related to (15)N/(14)N in urea-N but not related to (15)N/(14)N of blood cells, creatinine, and feces. The proportion of urea-N derived from body protein increased above 0.46 as N balance fell below -200 mg N kg(-0.75) d(-1). Proportions of urea-N from body protein were -0.01 +/- 0.21 in pregnant females before and after caging and were consistent with average body protein gain in winter. Storage of protein allows reindeer and caribou to tolerate diets that are low in N without impairing fetal development.

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Subadult bears were studied during their autumn hyperphagia (n = 3) and winter dormancy (n = 6). Urea kinetics were measured with 14C- and 15N-urea, protein turnover was estimated with 15N-glycine, and body composition was assessed with 3H-water. Reduced amino acid degradation in winter was indicated by declines in plasma urea and aminotransferase activities, and lower urea production than in autumn (4.7 vs. 27.5 mmol urea-N∙kg−0.75∙d−1). Only 7.5% of urea produced in hyperphagic bears was degraded and just 1.1% of the degraded N reutilized as amino-N. Dormant bears reutilized 99.7% of urea produced, indicating thorough microbial ureolysis and urea-N resorption. Low rates of body N loss during dormancy suggested losses of non-urea N as creatinine. Protein turnover rates (15.2–21.5 g∙kg−0.75∙d−1) were similar between seasons and reflected the apparent maintenance of hepatic, intestinal, and muscular functions through dormancy. Protein synthesis accounted for 32% of energy expended in dormancy, which was mainly (91.5%) derived from fat oxidation. Consistent organ function and body temperature in dormant bears enables recycling of urea-N, which minimizes body protein loss and conserves mobility. In comparison with heterothermic hibernation, ursid dormancy would provide greater flexibility during winter and facilitate rapid resumption of foraging and growth in spring.