In Vitro Analysis of Rumen Microbial Fermentation at Different Temperatures

Changes in ambient temperature can induce different responses in rumen temperature and consequently affecting the optimal conditions for microbial fermentation. Besides rumen pH and anaerobic conditions, rumen temperature is another important factor that can compromise VFA production in the rumen of dairy cows. In vitro analysis of microbial fermentation can provide relevant information on how temperature can affect this fundamental biological process for ruminants. Ruminal fluid (~1.5 L) was collected from three lactating cows with a ruminal cannula from the anterior, dorsal and mid-ventral region of the rumen and pooled. Then, this mixture was filtered through four layers of cheesecloth, and 50 mL of the final liquid were added to each digestion bottle. The Ankom RF gas production system was used to monitor the kinetics of microbial metabolism through measurement of cumulative pressure over 30 h of incubation at 36 °C (T36), 39 °C (T39), and 42 °C (T42). At least three digestion bottles were used as replicates for each temperature treatment, and an empty bottle used a correction factor. A previously dried and ground TMR sample (~1g/bag) was used to determine NDF and ADF digestibility during the incubation period. Rumen fluids were analyzed for ammonia N and VFA before and after the incubation period. Data were analyzed using the MIXED procedure of SAS. An interaction (P < 0.01) of Temperature × Time was observed. This effect was mainly attributed to the lower (P ≤ 0.05) cumulative pressure over time in the T42 treatment from 1 h incubation in comparison to T36 and T39. The cumulative pressure was overall similar (P = 0.45) between T36 and T39 treatments, but lower (P ≤ 0.2) for T42. Preliminary data suggest that rumen bacteria can sustain moderate increments in temperature, however, higher temperatures impaired rumen microbial fermentation. Further analysis of other parameters will provide a more comprehensive understanding of these results.