1 October 2011

5 minute read

Excess hydrogen produced during rumen fermentation is used by methanogenic bacteria to reduce CO2 to CH4 (methane). Ruminant livestock produce 80–115 million tons of CH4 annually, equivalent to 15–20 per cent of total anthropogenic CH4 production.

Garlic contains allicin, diallylsulide, dialyldisulfide and allyl mercaptan, which affect rumen methanogens, decreasing rumen CH4 and acetate production and increasing rumen propionate and butyrate production (Busquet et al., 2005).

The effect of garlic oil (GAR) was evaluated using batch cultures of rumen liquor (RL) fed with a 50:50 wheat straw to concentrate mixture with GAR (150, 300 or 450 mg/L) or without GAR (control). The incubations were carried out in 100 mL calibrated glass syringes as described by Menke et al. (1979) and Menke and Steingass (1988).

After 24 hours of incubation, gas samples were withdrawn from the tips of the incubation syringes using Hamilton gas-tight syringes and analysed for CH4 using gas chromatography. In vitro dry matter (DM) digestibility was estimated according to Goering & Van Soest (1970) and concentrations of volatile fatty acids were determined using gas chromatography.

Ten lactating Murrah buffaloes (second to third lactation) were randomly allocated to a control diet with or without GAR. The control diet consisted of concentrate, berseem and wheat straw in a ratio of 35:25:40 and was fed for 120 days.

A seven day digestion trial was conducted in mid- experiment. CH4 emission from animals was measured using the sulphur hexaluoride tracer technique. Data were analysed using analysis of variance for a randomised block design with three (in vitro study) or ive (in vivo study) replicates. Results are expressed as the mean ± SE. Critical difference was used to compare mean values.

Statistical significance was accepted at P < 0.05. In the in vitro trial, GAR concentrations of 150, 300 and 450 mg/L of RL all decreased DM digestibility (Table 1). This contrasts with the results of Busquet et al. (2005), who reported that GAR concentrations of 30 and 300 mg/L of RL did not affect the digestibility of DM, organic matter (OM), neutral detergent fibre or acid detergent fibre in a 50:50 forage:concentrate diet. Moreover, Yang et al. (2007) observed that garlic and berry essential oil did not affect total-tract digestibility of DM, OM, fibre or starch, but rumen DM and OM digestibility were increased.

In our in vitro study, acetate concentration and the proportions of propionate and butyrate were decreased by all levels of GAR. The acetate:propionate ratio was also decreased by GAR. These results are in accordance with those of Busquet et al. (2005). In our in vitro study, GAR decreased CH4 production (P < 0.05) at all doses; 99 per cent of methane production was inhibited at GAR doses of 300 and 450 mg/L of RL. Hart et al. (2006) investigated the effect of a commercially available aqueous allicin product using the Rusitec technique. Allicin had no effect on VFA production but CH4 production was decreased by 94 per cent by 20 mg/L RL of allicin.

The addition of GAR to the diets of lactating buffaloes decreased CH4 production (P < 0.05) in absolute terms (g) and in terms of g/kg digested DM and mM/kg DM intake. Total CH4 emission (g) and CH4 emission in terms of g/kg DM intake were reduced (P < 0.05) by 70 per cent by GAR (Table 2). These results confirm those of other studies in which various garlic products have been shown to decrease CH4 production (Busquet et al., 2005; Hart et al., 2006).

Busquet M, Calsamiglia S, Ferret A, Carro MD, Kamel C (2005) Effect of garlic oil and four of its compounds on rumen microbial fermentation. Journal of Dairy Science 88, 4393–4404. Goering HK, Van Soest PJ (1970) Forage Fiber Analysis (apparatus, reagents, procedures, and some applications). Agricultural Handbook 379. United States Department of Agriculture, Washington, DC.

Hart KJ, Girdwood SE, Taylor S, Yanez-Ruiz DR, Newbold CJ (2006) Effect of allicin on fermentation and microbial populations in the rumen simulating fermentor Rusitec. Reproduction Nutrition Development 46 (Suppl. 1), S97.

Menke KH, Steingass H (1988) Estimation of the energetic feed value obtained by chemical analysis and in vitro gas production using rumen luid. Animal Research Development 28: 7–55.

Menke KH, Raab L, Salewski A, Steingass H, Fritz D, Schneider W (1979) The estimation of digestibility and metabolizable energy content of ruminant feedstuffs from gas production when incubated with rumen liquor in vitro, Journal of Agricultural Science (Cambridge) 92, 217–222.