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Trabajo presentado al: XIIIth International Symposium on Ruminant Physiology (ISRP), P 68. 3-6 de septiembre de 2019. Leipzig (Alemania)., Despite their bad reputation among some nutritionists, it is nowadays widely accepted that tannins can be used as additives to modulate rumen fermentation. However, there is a void of information about which of the many types of tannins and at which doses may be more useful for a particular purpose. Furthermore, little is known about potential synergistic effects of different combinations of tannins. An in vitro assay with batch cultures of rumen microorganisms, using cannulated ewes as donors of rumen inocula, was performed to try to move forward on this subject. Commercial extracts of quebracho, oak and grape tannins, at doses selected from a previous study were combined following a simplex centroid design (in total, 10 combinations plus 1 control without tannins) and added to the incubation substrate (a total mixed ration based on alfalfa hay and concentrates, with 27% of starch and a F:C ratio of 40:60). Results suggested that there might be a synergistic effect of the combinations. For instance, none of the tannin extracts alone altered methane production, while some mixtures (mentioned below) did it, and the reductions of NH3-N, which would support a protection of dietary protein against ruminal degradation, were higher when combinations were used. Considering all the results together, we selected the next 3 treatments as the most convenient (doses are reported as % of incubated DM; real amounts after considering the simplex centroid design). Combination 1: 1.7% oak + 0.85% grape. This treatment induced lower gas and methane productions, ammonia-N concentration and molar proportion of minor volatile fatty acids (VFA; namely isobutyrate, isovalerate, valerate and caproate). Combination 2: 1.13% quebracho + 1.13% oak + 0.57% grape. Although this treatment affected negatively the ruminal disappearance of NDF (-8%), which would challenge its selection, it reduced gas and methane productions, ammonia-N concentration and molar proportion of minor VFA, as well as the acetate/propionate (A/P) ratio, and also increased the molar proportion of propionate. Combination 3: 0.57% quebracho + 2.27% oak + 0.28% grape. It reduced gas and methane productions, ammonia-N concentration, molar proportion of minor VFA, and the A/P ratio. This was the treatment with the strongest effect on NH3-N concentration (-22%). It also increased molar proportions of propionate and acetate, and it did not exert non-desirable effects on the in vitro ruminal fermentation parameters that were investigated. In closing, an appropriate combination of tannins may improve ruminant diet utilization while reducing methane emissions.

XIIIth International Symposium on Ruminant Physiology (ISRP), P 27. 3-6 de septiembre de 2019. Leipzig (Alemania)., Diet-induced milk fat depression (MFD) is presumably caused by the effects of ruminal biohydrogenation intermediates with antilipogenic activity. However, in marine lipid-induced MFD the involvement of t10c12-CLA, which is the only intermediate shown unequivocally to inhibit milk fat synthesis in ruminants, has been questioned, particularly in sheep. Thus, we conducted a meta-analysis to summarize the relationship between milk t10c12-CLA concentration and milk fat traits in lactating ewes. A database comprising 23 trials conducted by our team has been used. Fifty-five dietary conditions were characterized and grouped in two major categories (experimental treatments): non-MFD and marine lipid-induced MFD. The non-MFD category included 40 diets without supplementation or supplemented with plant oils and extracts, which modified the fatty acid profile of milk without detrimentally affecting milk fat synthesis. The marine lipid-induced MFD group comprised 15 diets supplemented with fish oil or microalgae. To ensure stable responses to diets, only the data collected after 21 or more days of adaptation were considered. Differences in diet formulation and chemical composition between the two groups of experimental treatments (non-MFD and MFD) were analyzed by one-way ANOVA. Linear and quadratic relationships between milk fat traits (yield and concentration of fat and yield of de novo synthesized and preformed fatty acids) and milk t10c12-CLA levels were examined using the MIXED procedure of SAS. Diet characteristics that may influence the response to lipid supplementation (e.g., forage:concentrate ratio, fibre concentration or starch content) did not differ between marine lipid-induced MFD and non-MFD groups. Prediction models showed an inverse linear relationship between t10c12-CLA and milk fat concentration in both treatments (R2=0.78; P0.10 for the treatment × t10c12-CLA level interaction). Similarly, milk fat yield was 23% lower in MFD than in non-MFD conditions (P, Spanish MINECO (AGL2017-87812 and Ramón y Cajal program) and European Regional Development Fund.

Trabajo presentado al: XIIIth International Symposium on Ruminant Physiology (ISRP), P 191. 3-6 de septiembre de 2019. Leipzig (Alemania)., Improvements in sustainability include the enhancement of feed efficiency, which in ruminant livestock might be associated with the diversity of the rumen microbiome. Results in the literature are inconsistent; efficient animals have been related with both high and low microbial diversity. However, no studies are available in dairy ewes. Therefore, we aimed at examining the relationship between feed efficiency, measured as residual feed intake (RFI), and rumen bacterial diversity in lactating sheep. The latter was estimated through the richness, Shannon and evenness indices, using T-RFLP and 3 enzymes: HhaI, MspI and HaeIII. The RFI is defined as the difference between the actual and expected feed intake, which was determined from feed requirements for maintenance and lactation according to the AFRC system. Animals with lower RFI eat less than predicted, being more efficient. Data from two studies performed by our team (with 20+15 animals fed a 50:50 F:C diet) were employed. Regression analyses were conducted to investigate the link between RFI and diversity measures. RFI averaged 0.29±0.062 (range: -0.75 to 1.01) and showed no significant relationship with most diversity indices. However, trends to significance (P, MINECO (AGL2017-87812 and programme Ramón y Cajal), JCyL (CSI276P18), FEDER and FSE.

Póster presentado al: 10th International Symposium on the Nutrition of Herbivores (ISNH).--Herbivore nutrition supporting sustainable intensification and agro-ecological approaches.-- p. 389. 2-6 de septiembre de 2018. Clermont-Ferrand (Francia)., Dietary addition of EPA, DPA, and DHA altered the abundance of several bacterial genera, such as Prevotella, Hallella, Paraprevotella and Succiniclasticum, that might participate in rumen biohydrogenation., Support by the Spanish MINECO (AGL2014-54587 and AGL2017-87812] and the European Regional Development Fund is acknowledged. D. Carreño benefits from a FPI and P. G. Toral from a Ramón y Cajal research contract.

Póster presentado al: 10th International Symposium on the Nutrition of Herbivores (ISNH).--Herbivore nutrition supporting sustainable intensification and agro-ecological approaches.-- p. 456. 2-6 de septiembre de 2018. Clermont-Ferrand (Francia)., Comparison of genes downregulated in lactating ewes showing CLA- or fish oil-induced milk fat depression highlights the involvement of several genes related to mammary lipogenesis., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO; AGL2014-54587-R and AGL2015-66035-R). P. G. Toral and B. Gutierrez-Gil benefit from Ramón y Cajal research contracts. Cofunding by the European Regional Development Fund is also acknowledged.

Resumen de la Comunicación oral al congreso e invitada: 10th International Symposium on the Nutrition of Herbivores (ISNH).-- Herbivore nutrition supporting sustainable intensification and agro-ecological approaches.-- p.766. 2-6 de septiembre de 2018. Clermont-Ferrand (Francia)., Growth in demand for foods with potentially beneficial effects on consumer health has motivated increased interest in developing strategies for improving the nutritional quality of ruminant-derived products. Manipulation of the rumen environment offers the opportunity to modify the lipid composition of milk and meat by changing the availability of fatty acids (FA) for mammary and intramuscular lipid uptake. Dietary supplementation with marine lipids, plant secondary compounds and direct-fed microbials has shown promising results. In this review, we have compiled information about their effects on the concentration of putative desirable FA (e.g., c9t11-conjugated linoleic acid and vaccenic, oleic, linoleic and linolenic acids) in ruminal digesta, milk and intramuscular fat. Marine lipids rich in very long-chain n-3 polyunsaturated fatty acids (PUFA) efficiently inhibit the last step of C18 FA biohydrogenation (BH) in the bovine, ovine and caprine, increasing the outflow of t11-18:1 from the rumen and improving the concentration of c9t11-18:2 in the final products, but increments in t10-18:1 are also often found due to shifts toward alternative BH pathways. Direct-fed microbials appear to favourably modify rumen lipid metabolism but information is still very limited, whereas a wide variety of plant secondary compounds, including tannins, polyphenol oxidase, essential oils, oxygenated FA and saponins, has been examined with varying success. For example, the effectiveness of tannins and essential oils is as yet controversial, with some studies showing no effects and others a positive impact on inhibiting the first step of BH of PUFA or, less commonly, the final step. Further investigation is required to unravel the causes of inconsistent results, which may be due to the diversity in active components, ruminant species, dosage, basal diet composition and time on treatments. Likewise, research must continue to address ways to mitigate negative side-effects of some supplements on animal performance (particularly, milk fat depression) and product quality (e.g., altered oxidative stability and shelf-life).

Póster presentado al: 10th International Symposium on the Nutrition of Herbivores (ISNH).--Herbivore nutrition supporting sustainable intensification and agro-ecological approaches.-- p. 459. 2-6 de septiembre de 2018. Clermont-Ferrand (Francia)., Pomegranate by-products can be used to enhance the content of potentially health-promoting fatty acids in ruminant meat and milk. Specific effects may vary depending on the by-product used., This study was supported by the VATC-20160394 research project (IGM, Leon).

Póster presentado al: 10th International Symposium on the Nutrition of Herbivores (ISNH).--Herbivore nutrition supporting sustainable intensification and agro-ecological approaches.-- p. 389. 2-6 de septiembre de 2018. Clermont-Ferrand (Francia)., Individual variation in the severity of milk fat depression cannot be explained by a single mechanism (e.g., changes in rumen VFA or biohydrogenation metabolites) but most probably by a complex combination of factors., This work was supported by the Spanish MINECO (AGL2014-54587-R). P. G. Toral benefits from a Ramón y Cajal research contract. Cofunding by the European Regional Development Fund is also acknowledged.