The effects of feed additives, essential oils or guanidinoacetic acid, on cattle rumen microbial fermentation in in vitro studies

Resumen

To improve rumen fermentation efficiency, two feed additives, essential oils (EO) and guanidinoacetic acid (GAA) were evaluated in three in vitro studies. In study 1, 12 EO: anise star, cassia, geraniol, lemongrass (LEM), limonene, thyme, tea tree, coriander (COR), capsicum, black pepper, turmeric and ginger (GIN), in Exp. 1 at three doses, and combinations of LEM, COR and GIN oils in Exp. 2, were added a 50:50 forage: concentrate diet. In Exp.1, LEM tended to increase the propionate proportion and tended to decrease the acetate to propionate ratio. Anise star, COR, and thyme tended to increase butyrate proportion. Capsicum, COR, and thyme decreased ammonia-N concentration. In Exp. 2, a synergy was observed between LEM and COR that increase total VFA and propionate proportion, and a decrease in the acetate to propionate ratio. However, the addition of high doses of GIN to the LEM + COR mix had an antagonistic effect on the rumen fermentation profile. In study 2, a blend of anise star and cassia oils (BAC) and LEM with four different carriers: silica-sunflower (SIL), rapeseed oil (RAP), diatomaceous earth (DIAT) and corn cob (CCO), were tested in vitro. In Exp. 1, treatments were: negative control, monensin (MON) as positive control, BAC, LEM, SIL, RAP, DIAT, CCO, LEM+SIL, LEM+RAP, LEM+DIAT and LEM+CCO. In Exp. 2, BAC and LEM were used to estimate total gas and methane production. All treatments were added a 50:50 forage: concentrate diet. In Exp. 1, BAC and LEM increased total volatile fatty acids, and SIL, RAP and CCO tended to increase total volatile fatty acids. Among the combinations of EO+carriers, only the combination LEM- RAP had an effect, decreasing ammonia-N concentration. In Exp. 2, BAC decreased total gas and methane production, and the ratio methane/total gas. In contrast, LEM increased total methane and the ratio methane/total gas. In study 3, 8 dual flow continuous culture fermenters were used in 2 periods (7 days adaptation and 3 days sampling). Treatments were arranged in a 2 × 2 factorial, with factors being the type of fermentation conditions: beef (pH between 5.5 and 6.5; diet 10:90 forage:concentrate, 16.3% CP and 17.6% NDF) or dairy (pH between 5.8 and 6.8; diet 50:50 forage:concentrate, 17.1% CP and 30.0% NDF); and GAA: 0 vs. 2 g/d. Temperature (38.5 ºC), liquid (0.10/h) and solid (0.05/h) dilution rates were kept constant. Diets (90 g/d DM) were fed in 3 portions/d. No differences were observed on true OM degradation. Degradation of NDF, the proportions of acetate and butyrate, the acetate to propionate ratio, NH 3 -N concentration, the flow of total N and ammonia N, the efficiency of microbial protein synthesis, and alpha and beta diversity of microbial population were higher in dairy than in beef. Total VFA and the propionate proportion were higher in beef than in dairy. The GAA increased NH 3 -N concentration and the flow of total and ammonia N. The microbial degradation of GAA was higher in dairy (69.8%) than in beef (6.30%) fermentation conditions.