Effects of Eucalyptus Citriodora Oil on Beef Cattle Ruminal Fermentation Characteristics on Continuous Culture System

The effects of Eucalyptus citriodra essential oil on OM digestion, microbial efficiency, pH, and ammonia levels using the continuous culture system technique were evaluated. Three Eucalyptus inclusions (0; 500 and 1,000 mg/kg of DM) were randomly assigned to continuous culture flasks (experimental unit; n = 9; 3 per treatment) following a completely randomized design. Culture flasks (1 L) were equipped with drainage system for effluent (which was collected and kept under refrigeration) and CO₂ plug on the lid. Inoculum (rumen fluid) for culture system was collected from 3 donors (steers; BW = 520 ± 30kg) for all batches (n = 2). Steers were fed diets containing 37% steam-flaked corn, 35% wet corn gluten feed, 25% roughage, and 3% supplement (DM basis). A 7-d incubation period was used for each batch, in which the first 3 d were used for the system adaptation followed by 4 d of collections. Continuous culture substrate was added twice daily, and contents collected at 0, 0.5, 1, 2, and 12 h post-feeding. Data were analyzed using the GLIMMIX procedures of SAS; day was used as repeated measure; and orthogonal contrasts were used to evaluate linear and quadric effects of Eucalyptus citriodra inclusion. No interaction treatment x time was observed for in vitro ruminal ammonia and pH (P = 0.98 and 0.99, respectively). Eucalyptus inclusion did not affect (P ≥ 0.83) in vitro ruminal ammonia, while in vitro ruminal pH decreased linearly (P < 0.01); in which 1,000 ppm dose showed a more acidic environment compared to other oil inclusions. Regardless of Eucalyptus inclusion, ruminal ammonia concentration peaked (P < 0.01) at 0.5 and 1h post in vitro system feeding time, while in vitro pH values reached the least (P < 0.01) levels at same collection times. No changes in true digestion of OM (P = 0.88), microbial efficiency (P = 0.31), NH₃ flow (P = 0.76), total N digestibility (P = 0.95), and microbial N flow (P = 0.38) were observed. Eucalyptus oil does not appear to negatively affect ruminal in vitro deamination or OM digestion. Increased acidity may confer potential positive effects on ruminal energetic load released within the first hour of fermentation post feeding.