Effects of Garlic Oil and Cinnamaldehyde on Sheep Rumen Fermentation and Microbial Populations in Rusitec Fermenters in Two Different Sampling Periods

SIMPLE SUMMARY: Garlic oil and cinnamaldehyde are plant-derived bioactive compounds with antimicrobial activity, which might contribute to improving the efficiency of rumen fermentation.

However, an apparent adaptation of microbial populations to these compounds is usually observed over time.

In this study, the effects of garlic oil and cinnamaldehyde on rumen fermentation and microbial populations were assessed in two periods of time using an in vitro system (Rusitec fermenters).

Despite this possible adaptation, garlic oil supplementation reduced methane production and enhanced the energy profile of fermentation end products over time, whereas cinnamaldehyde appeared to increase the microbial protein supply to the animal.

Thus, the use of these compounds as feed additives could contribute to increasing the efficiency and sustainability of ruminant production systems, bringing both economic and environmental benefits.

ABSTRACT: Garlic oil (GO) and cinnamaldehyde (CIN) have shown potential to modify rumen fermentation.

The aim of this study was to assess the effects of GO and CIN on rumen fermentation, microbial protein synthesis (MPS), and microbial populations in Rusitec fermenters fed a mixed diet (50:50 forage/concentrate), as well as whether these effects were maintained over time.

Six fermenters were used in two 15-day incubation runs.

Within each run, two fermenters received no additive, 180 mg/L of GO, or 180 mg/L of CIN.

Rumen fermentation parameters were assessed in two periods (P1 and P2), and microbial populations were studied after each of these periods.

Garlic oil reduced the acetate/propionate ratio and methane production (p < 0.001) in P1 and P2 and decreased protozoal DNA concentration and the relative abundance of fungi and archaea after P1 (p < 0.05).

Cinnamaldehyde increased bacterial diversity (p < 0.01) and modified the structure of bacterial communities after P1, decreased bacterial DNA concentration after P2 (p < 0.05), and increased MPS (p < 0.001).

The results of this study indicate that 180 mg/L of GO and CIN promoted a more efficient rumen fermentation and increased the protein supply to the animal, respectively, although an apparent adaptive response of microbial populations to GO was observed.