04169nam a2200169 a 450000100080000000500110000800800410001910000200006024501050008026000650018530000110025052036940026165000120395565000110396765000110397865000100398910541112015-12-10       2015    bl uuuu  m   00u1 u    #d1 aDE BARBIERI, I.  aNutritional and genetic regulation of the sheep rumen microbiome, PhD Thesis.h[electronic resource]  aNew England, NSW, Australia: University of New Englandc2015  a239 p.  aThe relationship between rumen microbial ecology and the host is regulated by multiple factors including diet, the microbial inoculum entering the gut, and host genetics. Two hypotheses associated with this statement were developed and tested during this project. The first focused on the relationship between diet, early life microbial inoculum and rumen microbiota and the second concentrated on the association between host genetics and gut microbial ecology. Hypothesis one was that the rumen microbiome of lambs could be altered by post-natal diet and by early-life microbial intervention, to achieve differences in rumen fermentation, development and animal performance that persist beyond weaning. Secondly, it was hypothesized that sheep with different genetic merit for wool growth harbour differences in their rumen microbiome that are associated with differences in gut morphology, physiology, digesta retention time and microbial protein outflow which underpin their wool phenotypes. To test the first hypothesis, performance of lambs was monitored from birth to post-weaning when the microbiome was modified by diet (inclusion of rumen-protected or rumen-active fat in the diet of the ewes during late pregnancy and of the lambs while suckling) and by postnatal introduction of digesta inoculum (from sheep on the same or on an alternate diet). The test of the second hypothesis was based on the study of Merino sheep genetically divergent for wool growth and assessed the association of animal wool phenotype with rumen microbial ecology, gut metabolism and anatomy. The first evaluation indicated that ruminal bacterial communities of lambs can be altered by both modifying the diet of the ewes and lambs during lactation, and by inoculating the rumen of the lambs during the first eight weeks of life. While both diet and inoculation affected species richness, biodiversity and taxonomy of the rumen communities, diet appeared to generate a greater and more lasting effect on rumen microbiota than did inoculation. Furthermore, while diet affected feed intake, rumen development and fermentation (reticulo-rumen weight, protozoa population, methane production), and inoculation with exogenous rumen fluid also moderated dry matter intake and some aspects of rumen fermentation (volatile fatty acids, protozoa population), the growth of wool or live weight of lambs and their condition score were not altered by either diet or inoculum. These findings suggest that while the rumen V microbiome may have plasticity in its taxonomic composition, microbial changes do not necessarily result in changed animal performance. In relation to the second hypothesis, study of Merino sheep with divergent genetic merit for clean fleece weight identified differences in bacterial community diversity and protozoa populations did exist between sheep with different genetic potential for wool production and these differences were conserved across feeding levels However, while the rumen microbiota and fleece production differed with genetic merit, no significant differences were apparent in the rumen fermentation, gut anatomy or digesta kinetics to provide a causal mechanism by which the microbiome was affecting animal performance. In conclusion, the rumen microbiome composition was shown to be related to the genetic attributes of the sheep host and was modified by early-life microbial interventions. Further research in using this knowledge to induce modifications in the rumen microbiota that can lead to lasting changes in the phenotype of the animals (eg. wool and body growth and composition, feed use efficiency and environmental impact per unit feed consumed) is required.  aCORDERO  aMERINO  aOVINOS  aRUMEN