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Abstract
The objective of this research was to determine the variation in the gastrointestinal microbial population of commercial Angus steers divergent in feedlot feed efficiency and the effect age, changes in diet, fasting, and gastrointestinal location have on it. In order to test these objectives, three experiments were conducted. The first study focused on the fecal microbiota of steers at weaning, yearling, and slaughter and found that several bacterial families consistently had divergent abundances despite changes in steers’ age and diet, highlighting the importance of bacterial families in determining the host feed efficiency as far back as weaning. The second study compared the ruminal microbiota pre- and post-slaughter and found that pre-slaughter fasting increased alpha-diversity and indicated some degree of dysbiosis. The third study compared the ruminal, cecal, and fecal microbiomes at slaughter of steers and found many links between steers’ feed efficiency and the bacterial population in their hindguts.