PSIV-A-2 - Evaluating the impact of filters on protozoa retention in dual-flow continuous culture systems

Abstract: The objective was to evaluate the effect of a felt-covered filter cover in dual-flow continuous culture (DFCC) fermenters on retaining protozoa in fermenter rumen fluid. In vitro rumen simulation techniques are best studied when the microbial community in the fermenters represents native rumen protozoa communities. Protozoa serve as the foundation for methanogenesis by providing hydrogen for rumen methanogens. Filter type could impact protozoa retention in a dual-flow fermenter system. Four DFCC fermenters were run for two periods consisting of 11 days with two control fermenters equipped with a conventional, 100-micron mesh filter (MF) and two fermenters equipped with a felt-covered filter (FF) over the 100-micron mesh filter. As it is crucial to maintain the fermenter rumen fluid anaerobic and in conditions like rumen conditions for the protozoa, all fermenters were adjusted to maintain pH in the range of 5-6 using a prepared continuous culture buffer solution distributed using a flow rate system. pH was recorded at h 0, 4, 8, and 12. Fermenter temperature was monitored to maintain 39 degrees Celsius and agitated at 50 rpm to support protein turnover. The fermenters were administered 44.6 g of feed substrate consisting of 38.45% dry corn, 30% corn silage, 10% grass hay, 12% distiller’s grain, 1.30% calcium carbonate, 0.25% trace mineral mix and 8% soybean meal on a dry matter basis at 12 h intervals. Protozoa were counted by collecting two 10 mL samples of the rumen fluid from each fermenter on days 1, 3, 5, 7, 9 and 11. Each sample was preserved with 10 mL of 37% formalin was diluted to a 1:200 sample-glycerol solution. Protozoa concentration was determined by placing 1 mL of the diluted sample solution on a Sedgewick-Rafter cell counting slide. Then, a microscope was used to record the number of holotricha and number of entodinium protozoa observed in 50 cells. Data were analyzed using a MIXED procedure of SAS. There was a treatment by hour interaction (P < 0.01) observed for pH; the FF fermenter had a greater pH at h 0 and 12 compared with the MF fermenter. No treatment by day effects were observed for holotricha and entodinium per mL (P > 0.45). Mean holotricha populations were 2,360,000 and 2,430,000 protozoa/mL for the MF and FF fermenters, respectively. Mean entodinium populations were 115,907 and 90,667 protozoa/mL for the MF and FF fermenters, respectively. Ammonia concentrations were not affected by the treatment (P = 0.34). Total volatile fatty acid concentrations displayed a treatment by hour interaction (P = 0.01); the MF fermenter had a greater concentration at h 0 and 4. While minor impacts on fermentation characteristics were observed, a felt-covered filter did not affect protozoa retention in a dual-flow continuous culture fermenters.