1196 Use of a novel continuous culture fermentor system for in vitro determination of enteric methane output from ruminants

Resumen

Continuous culture fermentor systems (CCFS) serve to evaluate the effect of diet on in vitro nutrient digestibility, fermentation, and microbial protein synthesis. Limitations of CCFS are: maintaining protozoa populations, and avoiding accumulation of undigested material in the vessels. Therefore, a 4-unit, 3-L bioreactor CCFS (Applikon Biotechnology Inc., Foster City, CA) was adapted to determine pH, DM, protozoa numbers, and enteric CH4 output of a forage diet. Each unit was fed 82 g DM/d of 50% orchardgrass (Dactylis glomerata) + 50% alfalfa (Medicago sativa) in equal portions, 4 times daily (07:30, 10:30, 14:00, and 19:00 h) throughout 10-d periods (n = 4, 7 d adaptation and 3 d collection). The CCFS was programmed to maintain temperature = 39°C, stirrer = 255 rpm, and CO2 flux = 1 mL/min. Temperature and pH were recorded every 2 min. On d 1 of each period, 1500 mL of rumen fluid + 32 g of digesta were collected from a fistulated cow and added to each fermentor. Vat volume was maintained at 1500 ± 200 mL during the 10 d. Solid mean retention time, solid dilution rate, and liquid dilution rate were adjusted daily to 24 h, 4%/h, and 11%/h, respectively, by regulation of buffer input and effluent removal. Effluent and fermentation vats were sampled daily to determine protozoa numbers and DM. Gas samples for CH4 analysis were collected 6 times daily (07:25, 09:00, 10:00, 13:55, 15:30, 16:30 h) during the 3-d collection periods and analyzed by GC (Varian CP 3800, Agilent Technologies, Santa Clara, CA). Data were analyzed using PROC GLIMMIX (SAS Inst. Inc., Cary, NC). There were no differences (P ≥ 0.067) in total buffer and effluent volume, effluent DM, and CH4 output between periods or among days within a collection period. There were no differences in pH or vat DM (P ≥ 0.445) between periods. However, pH was greater (P < 0.001) on d 10 than d 8 or d 9 (6.51, 6.43, and 6.45, respectively). Preliminary results show fewer (P < 0.001) protozoa during the adaptation vs. collection period (11.5 ± 2.82 × 104 and 34.0 ± 3.95 × 104 cells/ml, respectively). There was no difference (P = 0.786) in protozoa during the 3 d of the collection period (34.0 ± 2.25 × 104cells/ml). This CCFS not only provides a stable fermentation environment, but also preserves protozoal populations, which better simulates in vivo ruminal fermentation conditions compared with previous CCFS methods.