Volatile fatty acids and methane production from browse species of Algerian arid and semi-arid areas

The objective of the study was to determine the in vitro rumen fermentation end-products of 10 browse species. Serum bottles containing 500 mg of substrate, 10 ml of sheep rumen fluid and 40 ml of buffered medium were incubated for 24 h. After incubation, pH, methane and volatile fatty acid (VFA) productions were recorded. There were differences among feedstuffs (p < .05) in pH and VFA production. Astragalus gombo resulted in the highest and Stipa tenacissima in the lowest VFA production. Gas production was highest for Medicago sativa and lowest for S. tenacissima. Methane production (ml/g DM incubated) varied greatly. The lowest methane production was for S. tenacissima and Arthrocnemum macrostachyum (11.4 and 11.5 ml/g DM, respectively) and the highest for M. sativa and A. gombo (25.8 and 22.7 ml/g DM, respectively). The differences among species shrank when methane was expressed per ml of total gas produced or per mol of VFA produced. This indicates that a lower methane production would be due to a low fermentability of the substrate incubated, rather than to a specific inhibitory effect on methanogenesis. Hence, the 10 browse species studied herein would show little potential for mitigating ruminal methane production