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Energy metabolism, methane production and digesta kinetics of camelids and ruminants adapted to arid environment

Dittmann, Marie Therese

Titre : Energy metabolism, methane production and digesta kinetics of camelids and ruminants adapted to arid environment

Auteur : Dittmann, Marie Therese

Etablissement de soutenance : ETH ZURICH


Living in arid environments poses different challenges to mammalian herbivores : Maintenance of a constant body temperature in extreme climatic conditions, coping with scarcity of water, and low food availability. This doctoral study aimed at investigating putative ecological adaptations to harsh environmental conditions in camelids and ruminants adapted to arid environments based on the following hypotheses : When compared to ruminants or other mammals from resource-rich environments, camelids and ruminants adapted to aridity, 1) have a lower metabolic rate, which would results in lower energy requirements, a reduced endogenous heat load and, consequently, less water lost to evaporative cooling ; 2) produce relatively lower amounts methane (CH4), because CH4 is a side-product of microbial fermentation of food in the foregut, which represents an energy loss for the animal ; 3) have longer food particle retention times than in the foregut to increase the digestibility. With respect to solute retention times they could either have long solute retention times, indicating a slow water turnover in a capacious foregut serving to store water, or short solute retention times in relation to particle retention times, which could mirror an increase in ‘digesta washing’ and the yield of microbial protein from the digesta. We tested these hypotheses in three camelid species – Bactrian camels (Camelus bactrianus), llamas (Lama glama) and alpacas (Vicugna pacos) – and four ruminant species adapted to arid environments – Soemmerring’s gazelle (Nanger soemmerringii), Arabian mountain gazelle (Gazella gazella), Speke’s gazelle (Gazella spekei) and Phillip’s dikdik (Madoqua saltiana phillipsi). After a two-week diet adaptation period to a pure lucerne diet, five to seven individuals of each species were kept in separate pens for approximately one week. There, food intake and nutrient digestibility were measured, and digesta retention times were determined via indigestible markers. Thereafter, animals underwent respiration measurements, where CH4 and CO2 production, and O2 consumption were measured for 24 h. This allowed the calculation of the resting metabolic rate (RMR). The measured values were generally compared to literature data from other ruminant or mammalian herbivore species adapted to resource-rich environments. Among ruminants, G. spekei and G. gazella showed RMRs higher than expected, while the RMRs of M. saltiana and N. soemmerringii were close to the mammalian average for basal metabolic rate (BMR). M. saltiana also had lower energy requirements than expected for a ruminant of that size. Camelids revealed generally lower energy requirements and metabolic rates than ruminants of the same body mass range. Methane production was not consistently lower in ruminant species with M. saltiana, G. spekei and G. gazella producing more CH4 than expected according to their body mass based on a equation from literature data of other ruminant species. N. soemmerringii produced less CH4 than expected. Camelids had a lower absolute CH4 production when compared to ruminants of the same body mass range, but when related to unit digestible fibre ingested (the main substrate for methanogenesis), no difference could be found between ruminants and camelids. With respect to retention times in the foregut, the ruminants investigated in this study did not differ from ruminants from resource-rich environments and showed no exceedingly long retention times. While particle retention times appeared to be dependent on the animals body mass and its natural died (consisting of grass or browse), solute retention times were related to particle retention times, indicating that the ratio of both is adapted to a species’ natural diet. Camelids too, did not have exceedingly long retention times and these animals appear to rely on the same digestive strategy as ‘cattle-type’ ruminants. Only the retention times of large particles were slightly longer than in ruminants. Taken together, the results of this project did not consistently confirm the assumptions. While the low energy metabolism in camelids could either mirror an ecological adaptation, or a characteristic of the entire lineage, aridity-adapted ruminants do not appear to have a consistently low energy metabolism, which could imply that these animals rely on other mechanisms to save energy. Methane production in the species investigated appears to rather depend on the composition of the diet, than to reflect a species-specific trait underlying environmental adaptations. Hence, enteric methanogenesis seems to be a mandatory side-effect of microbial fermentation in the forestomach of ruminants and camelids. Retention times appear to have evolved to meet the requirements of a particular diet in ruminants, rather than to cope with scarcity in food or water. The slightly longer retention times of large particles in camelids could increase digestibility, but they could also simply mirror a difference in the sorting mechanism in the forestomach when compared to ruminants. The longer retention of large particles could also be a factor limiting food intake in camelids, which could reflect their comparatively low energy metabolism. Taken together, the three parameters investigated in this project revealed no mandatory adaptations of to habitats characterised by scarcity in food and water. Rather than single necessary adaptations, it is probably a combination of different resource saving mechanisms that enables aridity-adapted ruminants and camelids to compete in harsh environments.



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Page publiée le 12 mars 2017, mise à jour le 30 novembre 2018