Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2011
Publication Date: 8/26/2011
Publication URL: http://naldc.nal.usda.gov/catalog/53898
Citation: Hall, M. 2011. Isotrichid protozoa influence conversion of glucose to glycogen and other microbial products. Journal of Dairy Science. 94:4589–4602. Interpretive Summary: Sugars are very digestible, but cows sometimes have decreased milk protein percentages or efficiency of protein use when they are fed sugars compared to other nonfiber carbohydrates such as starch. Does something affect the amount of nutrients that sugars provide? The goal of this study was to determine if one type of rumen microbe, isotrichid protozoa, had an influence on the conversion of glucose to glycogen and transformation of glucose into fermentation products. The research showed that rumen microbes (which help cows digest feed and also serve as an excellent source of protein for cows) that were given glucose stored 9% of the glucose as glycogen instead of fermenting it immediately when isotrichid protozoa were present. When isotrichid protozoa were eliminated, 18% more microbial protein was made and less glycogen was stored. Learning more about factors which affect the products that rumen microbes make from sugars will allow us to better predict how to use sugars in formulating diets to meet the cow’s dietary requirements.
Technical Abstract: The goal of this in vitro study was to determine the influence of isotrichid protozoa (IP) on the conversion of glucose (Glc) to glycogen (Glyc) and transformation of Glc into fermentation products. Treatments were ruminal inoculum mechanically processed to destroy IP (B+, verified microscopically) or not mechanically processed (B-). Accumulated microbial Glyc was measured at 3 h of fermentation with (L+; = protozoa + bacteria) or without (L-; = predominantly protozoa) lysis of bacterial cells in the fermentation solids with 0.2 N NaOH. Two 3-h in vitro fermentations were performed using Goering–Van Soest medium in batch culture vessels supplemented with 78.75 mg Glc vessel-1 in a 26.5-mL liquid volume. Rumen inoculum from two cannulated cows was filtered through cheesecloth, combined, and maintained under CO2 for all procedures. At 3 h, 0.63 and 0.38 mg of Glc remained in B- and B+. Net microbial Glyc accumulations (and Glc in Glyc as % of added Glc) detected at 3 h of fermentation were 3.32 (4.69%), -1.42 (-2.01%), 6.45 (9.10%), and 3.65 (5.15%) mg for B-L-, B+L-, B-L+, and B+L+, respectively. B+ and L+ gave lower Glyc values than B- and L-, respectively. B+L- demonstrated net utilization of a-glucan contributed by inoculum with no net Glyc production. With destruction of IP, total Glyc accumulation declined by 44%, but estimated bacterial Glyc increased. Microbial accumulation of N increased 17.7% and calculated CH4 production decreased 24.7% in B+ compared to B-, but accumulation of C in microbes, production of organic acids or C in organic acids, calculated CO2, and carbohydrates in cell-free media did not differ between B+ and B-. Given the short 3-h time frame, increased N accumulation in B+ was attributed to decreased Glyc sequestration by IP rather than decreased predation on bacteria. After correction for estimates of C from AA and peptides utilized by microbes, 15% of substrate Glc C could not be accounted for in measured products in B+ or B-. Energetic costs for substrate Glc transport and Glyc synthesis consumed approximately 30% of substrate Glc. The substantial accumulation of Glyc, and changes in microbial N and Glyc accumulation related to IP presence, suggest that these factors should be considered in predicting profiles and amounts of microbial products and yield of nutrients to the cow as related to utilization of glucose. Determination of applicability of these findings to other soluble carbohydrates could be useful.