Effects of dose and adaptation time of a specific blend of essential oil compounds on rumen fermentation

Essential oils can be used as natural additives in animal feeds. The present study evaluated the effects of three different doses and different adaptation times of a specific blend of essential oils (BEO) on rumen microbial fermentation. Eight dual flow continuous culture fermenters (1320 ml) were used in two periods of 9 days each to study the effects of increasing doses of BEO. Treatments were: CTR (no BEO), D5 (5 mg/l of BEO), D50 (50 mg/l of BEO) and D500 (500 mg/l of BEO). During the last 3 days, samples were taken at 0, 2, 4 and 6 h after the morning feeding and analyzed for large peptide (LPep), small peptides plus amino acid (SPep + AA) and ammonia N concentrations, and at 2 h after feeding for volatile fatty acids (VFA) concentration and profile. The D5 increased total VFA concentration, acetate proportion and acetate to propionate ratio, and decreased propionate and valerate proportion, compared with CTR. The concentration of LPep N tended (P=0.08) to be lower for D5 compared with CTR. In the second experiment, eight sheep were used to study the effects of long-term adaptation of rumen fluid to BEO on ruminal fermentation. Four sheep were assigned at random to the CTR treatment (no BEO) and four sheep were adapted to BEO (110 mg/day of BEO) for 4 weeks (ADBEO). After 4 weeks samples of ruminal fluid were obtained at 0 and 3 h after the morning feeding and in 2 consecutive days using an oro-ruminal probe. Samples were analyzed for LPep, SPep + AA and ammonia N concentrations, total and individual VFA, and pH. Treatment ADBEO tended (P<0.10) to increase acetate proportion and decrease valerate proportion, compared with CTR. Ruminal fluid collected from each of CTR and ADBEO sheep was used to study in vitro fermentation profile of soybean meal, corn meal, alfalfa hay and ryegrass hay. Treatments were: Control fluid (CTR without BEO), CTR fluid plus a single dose of BEO (11 mg/l; CTR + BEO) and ADBEO fluid plus a single dose of BEO (11 mg/l; ADBEO + BEO). Acetate proportion and acetate to propionate ratio was higher, and propionate and isovalerate proportion, and BCVFA and ammonia N concentration were lower in ADBEO + BEO fluid compared with CTR fluid. The addition of essential oils can shift the microbial fermentation in the rumen by increasing the acetate to propionate ratio and inhibiting deamination.