This study is the first to evaluate the effects of five seaweeds (Ulva sp., Laminaria ochroleuca, Saccharina latissima, Gigartina sp., and Gracilaria vermiculophylla) on gas and methane production and ruminal fermentation parameters when incubated in vitro with two substrates (meadow hay and corn silage) for 24 h. Seaweeds led to lower gas production, with Gigartina sp. presenting the lowest value. When incubated with meadow hay, Ulva sp., Gigartina sp. and G. vermiculophylla decreased methane production, but with corn silage, methane production was only decreased by G. vermiculophylla. With meadow hay, L. ochroleuca and S. latissima promoted similar methane production as the control, but with corn silage, L. ochroleuca increased it. With the exception of S. latissima, all seaweeds promoted similar levels of total volatile fatty acid production. The highest proportion of acetic acid was produced with Ulva sp., G. vermiculophylla, and S. latissima; the highest proportion of butyric acid with the control and L. ochroleuca; and the highest proportion of iso-valeric acid with Gigartina sp. These results reveal the potential of seaweeds to mitigate ruminal methane production and the importance of the basal diet. To efficiently use seaweeds as feed ingredients with nutritional and environmental benefits, more research is required to determine the mechanisms underlying seaweed and substrate interactions.

The effects of supplementation with rapeseed, sunflower, and linseed oils (0.5 kg/d; good sources of oleic, linoleic, and linolenic acids, respectively) on milk responses and milk fat fatty acid (FA) profile, with special emphasis on rumen-derived biohydrogenation intermediates (BI), were evaluated in a replicated 4 x 4 Latin square study using 16 grazing dairy cows. The dietary treatments were 1) control diet: 20-h access to grazing pasture supplemented with 5 kg/d of corn-based concentrate mixture (96% corn; CC); 2) RO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of rapeseed oil; 3) SO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of sunflower oil; and 4) LO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of linseed oil. Milk fatty acids were converted to methyl esters and analyzed by gas-liquid chromatography and silver-ion HPLC. Dietary treatments had no effect on milk production or on milk protein content and milk protein production. Supplementation with rapeseed and sunflower oils lowered milk fat content and milk fat production, but linseed oil had no effect. Inclusion of dietary vegetable oils promoted lower concentrations of short-chain (including 4:0) and medium-chain FA (including odd- and branched-chain FA) and 18:3n-3, and higher concentrations of C(18) FA (including stearic and oleic acids). The BI concentration was higher with the dietary inclusion of vegetable oils, although the magnitude of the concentration and its pattern differed between oils. The RO treatment resulted in moderate increases in BI, including trans 18:1 isomers and 18:2 trans-7,cis-9, but failed to increase 18:1 trans-11 and 18:2 cis-9,trans-11. Sunflower oil supplementation resulted in the highest concentrations of the 18:1 trans-10, 18:1 cis-12, and 18:2 trans-10,trans-12 isomers. Concentrations of 18:1 trans-11 and 18:2 cis-9,trans-11 were higher than with the control and RO treatments but were similar to the LO treatment. Concentration of BI in milk fat was maximal with LO, having the highest concentrations of some 18:1 isomers (i.e., trans-13/14, trans-15, cis-15, cis-16), most of the nonconjugated 18:2 isomers (i.e., trans-11,trans-15, trans-11,cis-15, cis-9,cis-15, and cis-12,cis-15), and conjugated 18:2 isomers (i.e., trans-11,cis-13, cis-12,trans-14, trans-11,trans-13, trans-12,trans-14, and trans-9,trans-11), and all conjugated 18:3 isomers. The LO treatment induced the highest amount and diversity of BI without decreasing milk fat concentration, as the RO and SO treatments had, suggesting that the BI associated with 18:3n-3 intake may not be the major contributors to inhibition of mammary milk fat synthesis.