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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

Citation

Lee, Chanhee (2020), 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, Dryad, Dataset, https://doi.org/10.5061/dryad.zcrjdfn99

Abstract

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 after feeding). Data were analyzed using the MIXED procedure of SAS in a Latin square design. Preplanned comparison between HF-C and LF-C were conducted and the main effects of HMTBa and IA and their interaction within the LF diets were examined. The LF-C diet decreased ruminal pH and the ratio of acetate to propionate, with no major changes detected in ruminal FA profile compared with HF-C. The alpha diversity for LF-C was lower compared with HF-C, and beta diversity also differed between LF-C and HF-C. The relative abundance of bacterial phyla and genera associated indirectly with fiber degradation was influenced by LF-C versus HF-C. As the main effect of HMTBa within the LF diets, HMTBa increased the ratio of acetate to propionate and butyrate molar proportion. Ruminal saturated FA were increased and unsaturated FA concentration were decreased by HMTBa, with minimal changes detected in ruminal bacterial diversity and community. As the main effect of IA, IA supplementation increased ruminal concentration of all branched chain volatile FA and valerate and increased the percentage of trans-10 C18 isomers in total FA. In addition, alpha diversity and the number of functional features were increased for IA. Changes in the abundances of bacterial phyla and genera were minimal for IA. Interactions between HMTBa and IA were observed for ruminal variables and some bacterial taxa abundances. In conclusion, increasing trans-10 C18 isomers did not decrease milk fat yield for LF-C versus HF-C when dietary PUFA level was similar. Supplementation of HMTBa increased biohydrogenation capacity, and supplemental IA increased bacterial diversity, possibly alleviating MFD. The combination of HMTBa and IA had no associative effects in the rumen and need further studies to understand the interactive mechanism.