Inclusion of the aerial part and condensed tannin extract from Cistus ladanifer L. in lamb diets – Effects on rumen microbial community and fatty acid profile

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This study was carried out to test the hypothesis that the inclusion of condensed tannins (CT) from Cistus ladanifer aerial part or extract in a diet composed of dehydrated lucerne and supplemented with 60 g/kg of soybean oil can modulate the rumen microbiome and increase the production of healthy biohydrogenation intermediates (BI). Hence, thirty-six lambs were used to evaluate the effect of 3 levels of C. ladanifer CT (0 %, 1.25 % and 2.5 % of CT) and two ways of CT supply (C. ladanifer aerial parts and C. ladanifer CT extract) on rumen fatty acids and volatile fatty acids profile and ciliate protozoa and bacteria community composition. The experiment lasted 35 days, and rumen samples were collected immediately after slaughter. Ciliate protozoa were analyzed by microscopic counting, and high-throughput 16 S rRNA gene sequencing was used to analyse rumen bacterial composition. Condensed tannins diets did not affect ruminal fermentation. The inclusion of C. ladanifer aerial part or extract in lamb diets did not increase the t11–18:1 in the rumen content. On the other hand, the t11–18:1 proportion was lower in the rumen of lambs fed both C. ladanifer diets and the highest level of extract diet when compared with the lowest level of extract diet and the diets without CT inclusion. Regarding the rumen microbiome, the total of ciliates was not influenced by the CT level in diets but decreased with the inclusion of C. ladanifer aerial part in the diet. Entodinium genus was strongly and positively related with both total BI and t11–18:1 and it also was the ciliate genus most negatively related with rumen estimate biohydrogenation (BH) completeness. Independently of the diets, the bacterial community of rumen content was dominated by Firmicutes (49.8 %) and Bacteroidetes (30.8 %) phyla. The Lachnobacterium was the genus most closely related with t11–18:1 and negatively related with 18:0 and BH completeness, which suggests that the Lachnobacterium plays an important role on the BH when diets without CT inclusion and lower dose of C. ladanifer extract was fed to lambs, being responsible for t11–18:1 ruminal production. Cistus ladanifer aerial part and extract influenced the ruminal microbial composition, but at the conditions used, the increase in the ruminal production of healthy BI was not observed, highlighting the inconsistent BH response to dietary CT and underlining the need to develop efforts to increase knowledge about this CT source and its interactions with other feed factors and with the ruminal microbial community.