The objective of this study was to evaluate the inclusion of a blend of essential oils and exogenous enzymes on in vitro ruminal fermentation (dual flow continuous culture fermenters). Ten fermenters with dual continuous flow and they each have 1.4 L capacity. The dilution rate of the liquid and solid content has maintained 10% and 5%.h⁻¹, respectively. The design was randomized complete block with 4 replicates. Two experimental periods, each one has 8 d, were considered a block. The ruminal fluid was collected from 5 Nellore steers with ruminal cannula. The experimental period has 8 d with a 5-d adaptation period and 3-d collection period. The diet composition on dry matter (DM) was 8.5% sugarcane bagasse, 82.5% corn, 5% soybean meal and 4% mineral mixture. Each fermenter received daily 100g of the diet (on DM) with additives includes, as follows: T1–300mg of monensin (0.012%, monensin from Tortuga); T2–essential oil (0.008%, Crina Ruminants); T3–blend of essential oil (0.008%, Crina Ruminants) and 300 mg of monensin (0.0024%, monensin from Tortuga); T4-blend of essential oil (0.008%, Crina Ruminants) and exogenous amylase (0.05%, Ronozyme Rumistar ); T5- blend of essential oil (0.008%, Crina Ruminants), exogenous amylase (0.05%, Ronozyme Rumistar) and exogenous protease (0.08%, Ronozyme Proact). In this study were evaluated short-chain fatty acids (SCFAs) and the apparent digestibility of DM and crude protein (CP). The data were analyzed by R software and the probability of 5% was considered as statistical difference. There were no statistical differences for all variable studied. The data demonstrate that the use of essential oils and exogenous enzymes and their associations must be studied further because they showed the same fermentation parameters than the monensin treatment. Thus, these additives represent a good alternative to monensin. Table 1. Production and ratio of SCFA, DM and CP digestibility on in vitro fermentation of diet with high concentrate level and different kind of additives

	Treatments					P-value
T1	T2	T3	T4	T5
Total SCFA, mM	149.99	143.44	142.03	147.91	152.10	0.801
SCFA %
Acetate	50.3	50.7	51.3	53.3	48.4	0.885
Propionate	34.4	27.2	26.8	27.4	34.1	0.465
Butyrate	9.5	17.4	17.0	14.7	12.4	0.176
Valerate	3.21	1.99	1.99	2.00	2.58	0.311
Acetate: propionate	1.57	1.94	1.95	1.90	1.54	0.575
Apparent digestibility (%)
DM	41.90	43.51	47.96	48.12	43.65	0. 614
CP	35.05	34.39	39.69	38.76	39.69	0.664