Biohydrogenation patterns in digestive contents and plasma of lambs fed increasing levels of a tanniferous bush (Cistus ladanifer L.) and vegetable oils

•High levels of Cistus ladanifer and oil reduces the extent of biohydrogenation.•High levels of Cistus ladanifer and oil increases the C18 fatty acid intermediates.•A new fatty acid ratio is proposed to identify the t10-shift in rumen.•Linolenic acid is also biohydrogenated through a t10-shifted pathway.

The effect of two levels of Cistus ladanifer and three levels of oil blend (soybean:linseed, 1:2) in a 1:1 forage-to-concentrate diet was evaluated regarding the extent of rumen biohydrogenation, the characterization of products formed in the rumen and their transfer to abomasum and plasma. Hence, we analyzed samples from rumen contents, abomasal digesta and plasma of thirty six Merino Branco lambs randomly assigned to 6 diets: 2 levels of C. ladanifer (50 vs. 200 g/kg DM) and 3 levels of oil blend (0 vs. 40 vs. 80 g/kg DM). The intake of high levels of C. ladanifer with oil tended (P < 0.1) to reduce the extent of biohydrogenation in rumen and abomasum to about 44% and 42% of completeness, respectively, while oil addition to diets containing 50 g/kg DM of C. ladanifer did not affect the extent of biohydrogenation, averaging 70% of estimated completeness. Thus, an interactive effect between C. ladanifer and oil was observed for the concentration of biohydrogenation intermediates (BI) transferred to abomasum and plasma, with diets containing 200 g/kg DM of C. ladanifer supplemented with oil presenting the highest BI concentration. This was reflected in a great accumulation of t10-18:1 in rumen when high levels of C. ladanifer and oil were fed to lambs, and this accumulation was also more clearly observed in abomasum and plasma. Linear relationships between 18:3n−3 with t10,c15-18:2 (r2 = 0.575, P < 0.001), and t10,c15-18:2 with t10-18:1 (r2 = 0.481, P < 0.001) in rumen were observed, which supports the hypothesis that these BI could be formed from the 18:3n−3 by a t10-shifted biohydrogenation pathway. Moreover, according to linear regressions we verified that the t10-/t11-18:1 ratio in the rumen and abomasum can be anticipated by analyzing the t10-18:1/(t11-18:1+c9,t11-18:2) ratio in blood plasma, becoming a valuable tool to predict changes in rumen biohydrogenation when high-starch low-forage diets are fed to ruminants.