Effects of diet fermentability and supplementation of 2-hydroxy-4-(methylthio)-butanoic acid and isoacids on milk fat depression: 2. Ruminal fermentation, fatty acid, and bacterial community structure

The experiment was conducted to understand ruminal effects of diet modification during moderate milk fat depression (MFD) and 2-hydroxy-4-(methylthio)-butanoic acid (HMTBa) isoacids on alleviating MFD. Five ruminally cannulated cows were used in a 5 × Latin square design with the following dietary treatments (dry matter basis): high-forage low-starch control 1.5% safflower oil (HF-C); low-forage high-starch (LF-C); LF-C supplemented HMTBa (0.11%; 28 g/d; LF-HMTBa); [(IA) 0.24%; 60 LF-IA]; IA (LF-COMB). consisted periods 21 d per period (14-d adaptation 7-d sampling). Ruminal samples collected determine fermentation characteristics (0, 1, 3, 6 h after feeding), long-chain fatty (FA) profile (6 bacterial community structure by analyzing 16S gene amplicon sequences (3 feeding). Data analyzed using MIXED procedure SAS (SAS Institute Inc., Cary, NC) design. Preplanned comparisons between HF-C conducted, main their interaction within LF diets examined. decreased pH ratio acetate propionate, no major changes detected FA compared HF-C. α-diversity for lower HF-C, β-diversity also differed relative abundance phyla genera associated indirectly fiber degradation influenced versus As effect diets, increased propionate butyrate molar proportion. saturated unsaturated concentration HMTBa, minimal diversity community. IA, supplementation all branched-chain volatile valerate percentage trans-10 C18 isomers total FA. In addition, number functional features IA. Changes abundances Interactions observed variables some taxa abundances. conclusion, increasing fermentability (LF-C vs. HF-C) rumen without profile. Supplementation biohydrogenation capacity, supplemental diversity, possibly combination had associative need further studies interactive mechanism.