Effect of pH and oxygen on conjugated linoleic acid (CLA) production by mixed rumen bacteria from cows fed high concentrate and high forage diets

Conjugated linoleic acid (CLA) production from linoleic acid (LA) was characterized, in a relationship to biohydrogenation (BH), with mixed rumen bacteria obtained from three cows fed a high concentrate diet (HCD; 630 g/kg) or a high forage diet (HFD; 770 g/kg) for 5 weeks. Mixed rumen bacteria were incubated with LA in a rumen fluid medium under various conditions. Rumen bacteria from cows fed HCD were more active (P < 0.05) in BH than those from cows fed the HFD at most tested pHs. Rumen bacteria from HFD fed cows produced mostly cis-9, trans-11 CLA at pHs higher than 6.2, but those from HCD fed cows produced more (P < 0.05) trans-10, cis-12 CLA than cis-9, trans-11 CLA at lower pHs. Production of cis-9, trans-11 CLA, positively correlated, and trans-10, cis-12 CLA inversely correlated, to pH with rumen bacteria from cows fed both diets (r(2)=0.88). Rumen bacteria from HCD fed cows accumulated about four times more cis-9, trans-11 CLA in aerobic conditions, versus anaerobic conditions, after 1 h of incubation. Overall, trans-10, cis-12 CLA producing rumen bacteria may be more acid-tolerant and aero-tolerant than cis-9, traps-11 CLA producing rumen bacteria. (c) 2005 Elsevier B.V. All rights reserved.