Effects of Increasing Doses of Condensed Tannins Extract from Cistus ladanifer L. on In Vitro Ruminal Fermentation and Biohydrogenation

(rockrose) is a perennial shrub quite abundant in the Mediterranean region, and it is a rich source in secondary compounds such as condensed tannins (CTs). Condensed tannins from were able to change the ruminal biohydrogenation (BH), increasing the 11-18:1 and 9, 11-18:2 production. However, the adequate conditions of the CTs used to optimize the production of 11-18:1 and 9, 11-18:2 is not yet known. Thus, we tested the effect of increasing the doses of CT extract (0, 25, 50, 75 and 100 g/kg dry matter (DM)) on in vitro rumen BH. Five in vitro batch incubations replicates were conducted using an oil supplemented high-concentrate substrate, incubated for 24 h with 6 mL of buffered ruminal fluid. Volatile fatty acids (VFAs) and long chain fatty acids (FA) were analyzed at 0 h and 24 h, and BH of 9-18:1, 9, 12-18:2 and 9, 12, 15-18:3, and BH products yield were computed. Increasing doses of CTs led to a moderate linear decrease ( < 0.001) of the VFA production (a reduction of 27% with the highest dose compared to control). The disappearance of 9-18:1 and 9, 12-18:2 as well as the production of 11-18:1 and 9, 11:18:2 was not affected by increasing doses of CTs, and only the disappearance of 9, 12, 15-18:3 suffered a mild linear decrease (a reduction of 24% with the highest dose compared to control). Nevertheless, increasing the CT dose led to a strong depression of microbial odd and branched fatty acids and of dimethyl acetals production (less than 65% with the highest dose compared to control), which indicates that microbial growth was more inhibited than fermentative and biohydrogenation activities, in a possible adaptative response of microbial population to stress induced to CTs and polyunsaturated fatty acids. The ability of to modulate the ruminal BH was not verified in the current in vitro experimental conditions, emphasizing the inconsistent BH response to CTs and highlighting the need to continue seeking the optimal conditions for using CTs to improve the fatty acid profile of ruminant fat.