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Impact of crude glycerin supplementation on rumen and duodenal microbial populations in beef cattle diets
The use of crude glycerin as a feed supplement in beef cattle diets may be an efficient energy source, but changes in ruminal microbial populations are undocumented. The objective of this experiment was to determine the effects of crude glycerin on the prevalence of five ruminal bacteria species (Selenomonas ruminantium, Anaerovibrio lipolytica, Fibrobacter succinogenes, Butyrivibrio fibrosolvens, and Megasphaera elsdenii). Seven ruminally and duodenally fistulated beef steers were used in a 4 diet, 4 period, 7 animal, column X row transformation design. Steers were fed 0%, 4%, 8%, and 12% glycerin in diets consisting of wheat straw, soybean hulls, and soybean meal. Glycerin replaced soybean hulls in the control diet. Samples were taken from ruminal and duodenal cannulas 8 hours post-feeding on the last day of a 21-day period. Total DNA was extracted from each sample and was quantified using real-time PCR with species-specific PCR primers. Real-time assays were performed using the SYBR Green reporter assay and relative fold change in the rumen and duodenum were calculated using the DD CT method relative to the control. Data was analyzed using the mixed procedures of SAS. The model included glycerin concentration, animal, and period. Contrasts were developed to test linear and quadratic change in species abundance relative to the control.
In the rumen, Selenomonas ruminantium linearly increased up to 18-fold at 12% glycerin supplementation (P = 0.02) and Anaerovibrio lipolytica linearly increased up to 14-fold at 8% glycerin supplementation (P < 0.01). Fibrobacter succinogenes, Butyrivibrio fibrosolvens, and Megasphaera elsdenii displayed no significant changes in the rumen (P > 0.27). In the duodenum, S. ruminantium and A. lipolytica linearly increased up to 9-fold (P < 0.001) and up to 8-fold (P < 0.001) at 8% and 12% glycerin supplementation, respectively. F. succinogenes and M. elsdenii showed no significant changes in the duodenum (P > 0.86). B. fibrosolvens quadratically increased up to 22-fold at 12% glycerin supplementation in the duodenum (P < 0.001). An increase in A. lipolytica is indicative of an increase in propionate which could increase G:F while an increase in S. ruminantium indicates an increase in lactate being produced in the rumen. An insignificant effect on F. succinogenes suggests that fiber digestion may not be negatively affected by an increase in dietary glycerin.
Keywords: Glycerin, microbial community, beef cattle