Utilización de Onobrychis viciifolia para modular el metabolismo ruminal y la biohidrogenación de ácidos grasos en la dieta

There is still controversy surrounding the ability of tannins to modulate the process of biohydrogenation (BH) of fatty acids (FA) in the rumen and improve the lipid profile of milk or meat without conferring a negative response in the digestive utilization of the diet. Based on this, the current work was performed with the aim of investigating the effect of dietary tannins (particularly those from sainfoin -Onobrychis vichfolia- hay) on the BH of linoleic (18:2n-6) and linolenic (18:3n-3) acids and on the ruminal fermentation. This study was carried out in vitro, using batch cultures of rumen microorganisms and the gas production technique. Rumen cannulated sheep were used as donors of microbial inocula. Two legume hays, alfalfa (virtually free of tannins) and sainfoin (with a similar chemical composition but containing 3.5 per cent total tannins, expressed as tannic acid equivalents), were utilized as incubation substrates. Both hays were enriched with either sunflower oil (as a source of linoleic acid) or linseed oil (as a source of linolenic acid). The analytical techniques included the determination of tannins, of the lipid profile of rumen contents (focused primarily on relevant metabolites such as 18:0, trans-11, trans-10 and cis-9 18:1, cis-9 trans-11 18:2 -the main isomer of the conjugated linoleic acid; CLA-, trans-11 cis-15 18:2, 18:2n-6 and 18:3n-3) and of some rumen fermentation parameters (e.g., gas production, ammonia concentration, dry matter disappearance, etc.). Most results related to intermediate BH metabolites (e.g., greater concentrations of 18:3n-3, 18:2n-6, trans-11 cis-15 18:2, cis-9 18:1 or total polyunsaturated FA in sainfoin incubations) show the ability of this legume, possibly due to its tannin content, to inhibit the ruminal BH of dietary unsaturated FA. On the other hand, no significant differences (P less than 0,10) were detected in the accumulation of cis-9 trans-11 CLA, total CLA or 18:0, and variations in trans-11 18:1 did not follow a regular pattern. Regarding the rumen fermentation, it was observed that gas production was lower in the incubations with sainfoin hay (-17 per cent), which is consistent with previous findings when using tannins. Accordingly, ammonia concentrations and total volatile fatty acid (VFA) production also presented smaller values with sainfoin (-23 per cent and - 11 per cent, respectively); differences in VEA being especially clear in the molar proportions of butyrate and valerate. Overall, the study shows the ability of Onobrychis vichfolia, probably by means of its moderate tannin content, to modify the ruminal BH of dietary unsaturated FA, which could result in improvements in the lipid profile of final products (meat and milk). Nonetheless, the present results are not as promising as expected or as obtained before with other nutritional strategies.