Efecto de la suplementación de la dieta con taninos y aceite de pescado sobre la biohidrogenación de los ácidos grasos y la fermentación ruminal in vitro

Supplementation of ruminant diets with marine lipids enables to increase the milk and meat content of some potentially health promoting metabolites, such as n-3 polyunsaturated fatty acids (FA). Furthermore, due to their ability to modulate the ruminal biohydrogenation (BH), these supplements may improve the concentration of the cis-9 trans-41 conjugated linoleic acid (CLA) isomer in ruminant-derived products. According to the literature, tannins also seem to be able to favourably modify the BH process, although it is unknown whether the combined use of both types of compounds might result in additive, synergistic or even antagonistic effects. This master thesis was therefore proposed to investigate the impact of diet supplementation with fish oil and tannins on the ruminal BH, as well as on the fermentation (with a view on their possible practical application). To this end, an in vitro assay using batch cultures of rumen microorganisms and the gas production technique was carried out and the following treatments were evaluated: Control, Fish (containing 1% fish oil), Oak (containing 2% of a commercial extract of oak tannins), Grape (containing 2% of a commercial extract of grape tannins), Fish plus Oak and Fish plus Grape (combinations of previous treatments). Cannulated sheep were used as donors of rumen innocula for the incubations. The lipid profile analysis revealed that fish oil-supplemented diets increased considerably the concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 and inhibited the last step of ruminal BH, reducing the formation of 18:0 and enhancing some trans 18:1 isomers, but not trans-11 18:1. A greater concentration of trans-11 trans-15 18:2 suggests that fish oil could also inhibit previous stages of BH, although this did not affect the accumulation of CLA isomers. Conversely, in the studied conditions, the administration of oak or grape tannins did not exert significant effects on ruminal BH, and their combination with fish oil did not cause variations in the FA profile other than those observed with the lipid supplement. The only exceptions were observed with the treatment Fish plus Grape and comprised a higher accumulation of cis-11 18:1, which might be due to an inhibition of its saturation to 18:0, and a small increase in the concentration of 17:0. In contrast, the proportions of other odd- and branched-chain FA, which have been used as microbial biomarkers, remained unaltered, probably suggesting that rumen bacterial populations were hardly affected by the experimental treatments. Regarding the rumen fermentation parameters, no significant differences were detected in the pH, ammonia, lactic acid or volatile FA concentrations, the gas production or the dry matter disappearance at 24h. Only the in vitro true digestibility and the molar proportion of isoacids showed a trend to be lower with some treatments (i.e., with oak in the former case and with the combination of fish oil and tannins in both). Hence, ruminal fermentation would not have been substantially impaired by the studied supplements. Overall, the results obtained in this work do not allow to recommend the combined use of fish oil and tannin extracts as an effective nutritional strategy to modulate ruminal BH and favour the accumulation of FA with potential benefits to consumer's health.