A flexible digestive strategy accommodates the nutritional demands of reproduction in a free-living folivore, the Koala (Phascolarctos cinereus)

1. Small mammalian folivores, such as the koala, are considered to be energetically limited by their relatively small gut capacity compared with metabolic requirements and the gut-filling effect of their poorly digestible leaf diet. However, during peak lactation, female koalas increase their food intake (35%) to meet the nutritional demands of reproduction.\ud \ud 2. This study examines mechanisms by which reproductive female koalas overcome limitations to food intake.\ud \ud 3. Digesta retention in the gastrointestinal tract was measured in free-living koalas using inert solute (cobalt (Co) complexed with EDTA) and particle markers (chromium (Cr)-mordanted to cell wall constituents' 600–1180 μm in diameter).\ud \ud 4. The whole gut rate of passage of both markers was 2–3 times faster than in captive koalas, probably because of 35%–69% greater food intakes in the wild. As in captive koalas, the solute marker was retained longer than the particle marker in free-living animals, indicating selective retention of fluid, solutes and small particles (including bacteria) in the hindgut caecum and proximal colon. The digesta retention of both markers were unaffected by the 35% increase in food intake associated with reproduction, largely due to a 42% increase in the solute marker pool size in lactating animals. The pool size of large particles in the digesta was unchanged.\ud \ud 5. Thus, female koalas meet the nutritional demands of reproduction at least partly by an increased solute digesta pool size, minimizing the detrimental effects of increased food intake on digestion of solutes and small particles, and on faecal loss of microbial protein. There was some indication that they also increase the passage rate of large particles or increase the efficiency of separation of large and small particles to reduce the gut-filling effects of large, poorly digestible particles.\ud \ud 6. Clearly the digestive strategy of the koala is more flexible, and limitations to food intake less stringent, than previously thought. Female koalas accommodate the increased food intake required to meet the demands of free-living and reproduction without compromising nutrient extraction from their eucalypt leaf diet. We suggest that similar flexibility in digestive strategy is likely to play an important role in the way that most small mammalian herbivores, especially arboreal folivores, meet the nutritional demands of reproduction

Digestive plasticity in Mallard ducks modulates dispersal probabilities of aquatic plants and crustaceans

1. The consequences of plastic responses of the avian digestive tract for the potential of birds to disperse other organisms remain largely uninvestigated. 2. To explore how a seasonal diet switch in Mallard (Anas platyrhynchos L.) influences their potential to disperse plants and invertebrates, we recorded the retention time of markers, following exposure to two diets of contrasting digestibility (trout chow vs seeds). 3. We then recorded the retrieval and germination of Fennel Pondweed (Potamogeton pectinatus L.) seeds and Brine Shrimp (Artemia franciscana Kellogg) cysts ingested by the same birds. 4. Gut passage rates of markers were increasingly longer in birds on the seed-based, high-fibre diet and shorter in birds on the animal-based, low-fibre one. 5. Propagule digestibility, and thus survival to gut passage, differed between diet groups, with more seeds and fewer cysts retrieved from ducks on the animal-based diet. Germination decreased with retention time, but was not affected by diet. 6. Differences in passage rates of markers but not of seeds and cysts suggest no change in dispersal distances of plants and invertebrates between seasons, while differences in digestibility would affect the numbers of propagules dispersed. [KEYWORDS: Artemia franciscana ; diet switch ; endozoochorous dispersal ; Potamogeton pectinatus]

Comparação do sistema de monitoramento computadorizado de digestão in vitro com os métodos in vivo e in situ: 2. Uso do resíduo da matéria seca de forragens Comparison of the in vitro digestion computerized monitoring system with in vivo and in situ methods: 2. Use of the dry matter residue of the forages

RESUMO - O objetivo deste trabalho foi comparar o sistema de monitoramento computadorizado da produção de gás in vitro com os métodos in vivo e in situ. Nas comparações, foram utilizadas silagens de milho com alto/baixo teores de matéria seca, com/sem inoculante. A digestibilidade das silagens com alto teor de matéria seca (MS), com/sem inoculação, não apresentou diferenças entre os métodos analisados. Quando avaliadas separadamente do efeito do inóculo, essas silagens diferiram nos métodos in vitro/gás e in situ, mas não no in vivo. Entretanto, quando analisadas somente sob efeito do inoculante, apenas no método in situ houve diferença. Não foram encontradas diferenças na digestibilidade da fibra em detergente neutro (FDN) das silagens com alta ou baixa MS, inoculadas ou não, bem como em relação ao pH ao final da digestão. Em conclusão, o desaparecimento da MS e FDN quantificada pelo resíduo no sistema in vitro/gás foi semelhante aos demais métodos avaliados.<br>ABSTRACT - The objective of this work was to compare the computerized monitoring of the in vitro gas production system with the in vivo and in situ methods. On the comparisons, corn silage with high/low dry matter contents, with/without inoculation, were used. The digestibility of silage with high dry matter (DM) content, with/without inoculation, did not present differences among the analyzed methods. When evaluated apart from the inoculation effect, that silage differed in vitro/gas and in situ methods; however in vivo did not differ. Nevertheless, when analyzed under the inoculation effect, only in in situ method there was no difference. No differences were found on the silage neutral detergent fiber (NDF) digestibility with high or low DM, inoculated or not, as well as in relation to pH at the end of digestion. In conclusion, the disappearing of DM and NDF determined by the residue of the in vitro/gas system was similar to the others evaluated methods