Dietary cardoon meal modulates the rumen biohydrogenation and bacterial community in lambs

Cardoon meal (CM) is a by-product from oil extraction of cardoon seeds (Cynara cardunculus var. altilis) and is rich in protein, unsaturated fatty acids (FA) and polyphenols. The consortium of microbes residing in the rumen of ruminant animals allows for better digestion of agro-industrial by-products (such as CM) utilized as animal feeds. Nutritional analysis and in vitro ruminal studies have demonstrated CM as a potential feed resource for ruminants, but no in vivo study has investigated the effect of CM on rumen function. This study examined the effect of CM on the ruminal fermentation, biohydrogenation of FA (RBH) and the rumen microbiota of lambs fed a concentrate diet containing either 15% dehydrated alfalfa (CON, n = 8) or CM (CMD, n = 7) for 75 days pre-slaughter. In comparison to CON, lambs fed CMD had lower dietary intakes of C18:3 n-3 (-26.7%) but greater intakes of C18:0 (+34.7%), C18:1 n-9 (+20.2%), C18:2 n-6 (+19.6%) and polyphenols (+117.1%). Dietary treatment did not influence ruminal fermentation characteristics and the absolute abundance of rumen bacteria, methanogens, fungi or protozoa. Feeding CMD promoted RBH resulting in a greater concentration (P < 0.05) of ruminal C18:0 (+71.7%) and total saturated FA (+41.3%) and lower C18:1 n-9 (-21.8%) and monounsaturated FA (-46.0%) compared to CON-fed lambs. In addition, the inhibition of RBH in CON-fed lambs resulted in a higher concentration of trans-10 C18:1, trans-11 C18:1, total odd- and branched-chain FA and total trans-18:1 isomer in the ruminal digesta. Dietary effect on RBH was accompanied by changes in the rumen bacterial community with lower population diversity indices observed in lambs fed CMD compared to CON. Lambs fed CMD displayed a greater relative abundance of Proteobacteria and a lower abundance of Bacteroidetes and Fibrobacteres compared to CON-fed lambs. At the genus level, CMD mediated a specific shift from Prevotella, Alloprevotella, Solobacterium and Fibrobacter to Ruminobacter, suggesting that these bacterial genera may play an important role in RBH. Canonical correspondence analysis indicated that the rumen bacterial community in CON fed lambs was positively correlated with cis-16 C18:1, trans-10 C18:1 and C18:3 n-3. Overall, results demonstrated that dietary replacement of dehydrated alfalfa with CM promoted RBH through modulation of the bacterial community.