Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2010
Publication Date: N/A
Technical Abstract: The goal of this in vitro study was to determine the influence of Isotrich spp. protozoa on the conversion of glucose (Glc) to glycogen (Glyc). In a 2 x 2 factorial, treatments were 1) ruminal inoculum mechanically processed to destroy Isotrich spp. (M+, verified microscopically) or not mechanically processed (M-), and 2) measurement of microbial Glyc accumulated by 3 h of fermentation with (L+; protozoa + bacteria) or without (L-; predominantly protozoa) lysis of the fermentation solids with 0.2 N NaOH for 15 min in a boiling water bath before Glyc analysis. Two 3 h in vitro fermentations were performed using Goering–Van Soest medium in batch culture vessels supplemented with 3 g Glc L-1. Rumen inocula from 2 cannulated cows filtered through 4 layers of cheesecloth were combined, and maintained under CO2 for all procedures. Fermentation vessel contents were transferred to centrifuge tubes using 0.9% NaCl, centrifuged twice at 13,000 x g for 45 min at 5°C, with pellet resuspended in 0.9% NaCl after the first centrifugation and supernatant decanted each time. Pellets were analyzed for Glyc using a Na acetate buffer, heat-stable, a-amylase and measurement of released Glc. Values for samples at 3 h of fermentation were corrected for 0 h values representing a-glucan introduced with inocula. Microbial Glyc 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 (% of added Glc) for M-L-, M+L-, M-L+ and M+L+, respectively (SED = 0.50). M+ gave lower Glyc values than M- (P<0.01), and L+ gave greater values than L- (P<0.01); there was an interaction of L and M (P=0.02). M+L- showed net utilization of a-glucan initially in the fermentation with no net Glyc production. Estimated bacterial Glyc was lower for M- (3.12 mg) than M+ (3.65 mg; P<0.01). Although destruction of Glyc-accumulating protozoa decreased detected Glyc by ~40%, sequestration of Glc by bacteria accounted for 4-5% of dosed Glc, with Glyc synthesis also representing an energetic cost. Potential decreases in microbial growth related to Glyc could require changes in protein supplementation to maintain protein supply to the ruminant host.