Metabolic fate of fatty acids involved in ruminal biohydrogenation in sheep fed concentrate or herbage with or without tannins

A 2 × 2 factorial experiment was carriedout to evaluate the effect of herbage or concentratefeeding and dietary tannin supplementation onfatty acid metabolism and composition in sheep ruminalfluid, plasma, and intramuscular fat. Twenty-eightmale lambs were divided into 2 equal groups at 45 d ofage and kept in individual pens. One group was givenexclusively fresh herbage (vetch), and the other groupwas fed a concentrate-based diet. Within each treatment,one-half of the lambs received supplementationof quebracho powder, providing 4.0% of dietary DM astannins. Before slaughter, blood samples were collected.The animals were slaughtered at 105 d of age, and ruminalcontents and LM were collected. Blood plasma,ruminal fluid, and LM fatty acid composition was determinedby gas chromatography. Tannin supplementationreduced (P < 0.05) the concentration of stearicacid (−49%) and increased the concentration of vaccenicacid (+97%) in ruminal fluid from concentrate-fedlambs. Within concentrate- and herbage-based diets,tannin supplementation reduced the accumulation ofSFA in blood (P < 0.05) compared with lambs fed thetannin-free diets. When tannins were included in theconcentrate, the LM contained 2-fold greater concentrationsof rumenic acid compared with the LM of thelambs fed the tannin-free concentrate (0.96 vs. 0.46%of total extracted fatty acids, respectively; P < 0.05).The concentration of PUFA was greater (P < 0.05)and SFA (P < 0.01) less in the LM from lambs fed thetannin-containing diets as compared with the animalsreceiving the tannin-free diets. These results confirm,in vivo, that tannins reduce ruminal biohydrogenation,as previously reported in vitro. This implies that tanninsupplementation could be a useful strategy to increasethe rumenic acid and PUFA content and to reducethe SFA in ruminant meats. However, the correctdietary concentration of tannins should be carefullychosen to avoid negative effects on DMI and animalperformance.