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 ruminal effects of HMTBa and isoacids on alleviating MFD. Five ruminally cannulated cows were used in a 5 × 5 Latin square design with the following 5 dietary treatments (dry matter basis): HF-C, a high forage and low starch control diet with 1.5% safflower oil; LF-C, a low forage and high starch control diet with 1.5% safflower oil; LF-HMTBa, the LF-C diet supplemented with HMTBa (0.11%; 28 g/d); LF-IA, the LF-C diet supplemented with isoacids (0.24%; 60 g/d; IA); and LF-COMB, the LF-C diet supplemented with HMTBa and IA. The experiment consisted of 5 periods with 21 d per period (14-d diet adaptation and 7-d sampling). Ruminal samples were collected to determine fermentation characteristics (0, 1, 3, and 6 h after feeding), long chain fatty acids (FA) profile (6 h after feeding), and bacterial community structure by analyzing 16S gene amplicon sequences (3 h af...