The effects of 6 doses (0 (control), 40, 80, 160, 320 and 640 mg/L incubation medium) of carvacrol (CAR), thymol (TYM), eugenol (EUG) and garlic oil (GO) on in vitro fermentation of a mixed diet (65:35 alfalfa hay:concentrate) were evaluated in batch cultures of mixed rumen microorganisms from the rumen of sheep fed the same diet. Previous in vitro studies have shown the ability of these compounds to modify ruminal fermentation, but the effects could be dose and diet dependent. After 24 h of incubation, the main fermentation variables were determined. Differences among treatments were declared at P 0.05) rumen fermentation at any other dose. TYM at 320 mg/L decreased (P < 0.05) total VFA, acetate, propionate and methane production, and increased (P < 0.05) acetate:propionate ratio compared with control. CAR has similar effects on VFA and propionate production at dose 160 mg/L, and tended (P = 0.08) to reduce methane production. At 320 mg/L, CAR also increased (P < 0.05) acetate:propionate ratio and decreased (P < 0.05) ammonia-N concentrations, compared with the control. These results confirm that essential oils supplementation shows different effects on ruminal fermentation depending on the administered dose and the nature of the compound. Under the conditions of this study the doses of essential oil that modified VFA profile and reduced methane production also resulted in a reduction in VFA production, which would indicate a decrease in feed digestibility and have negative consequences on animal productivity.

1 página.-- Trabajo presentado al Joint Meeting of the ADSA-PSA-AMPA-CSAS-ASAS (Phoenix, Arizona, Estados Unidos, del 15 al 19 de Julio, 2012).

Peer reviewed