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Effects of 2-hydroxy-(4-methylthio) butanoic acid and isoacids on rumen fermentation, production, and milk fatty acid during mild milk fat depression in lactating cows.

J. E. Copelin

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06-24-2020

Abstract:

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Effects of 2-hydroxy-(4-methylthio) butanoic acid and isoacids on rumen fermentation, production, and milk fatty acid during mild milk fat depression in lactating cows.
J. E. Copelin*1, J. L. Firkins2, M. T. Socha3, C. Lee1. 1Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University Wooster, OH, 2Department of Animal Sciences, The Ohio State University Columbus, OH, 3Zinpro Corporation Eden Prairie, MN.

The objective of this experiment was to determine effects of 2-hydroxy-(4-methylthio) butanoic acid (HMTBa), isoacids (isobutyrate, isovalerate, 2-methylbutyrate, valerate) or their combination on alleviation of milk fat depression (MFD). Ten Holstein cows (5 cannulated and 5 non-cannulated) were used in a repeated 5 � 5 Latin square design. Treatments included 1) high forage diet (HF; 33% NDF, 24.0% starch, and 3.5% PUFA on a DM basis), 2) low forage diet (LF; 29% NDF, 29% starch, and 3.5% PUFA), 3) LF with HMTBa at 0.1% (DM basis; LF-HMTBa), 4) LF with isoacids (60 g/d; equal amounts of all isoacids; LF-IA) and LF supplemented with both HMTBa and IA. Data were analyzed using the Mixed procedure of SAS [random effect, square and cow(square); fixed effect, diet]. Preplanned contrasts were used to compare HF vs. LF and to examine the effect of HMTBa, IA, or their interaction compared with LF. Molar proportion of propionate increased (P < 0.01) and acetate decreased (P = 0.10) for LF vs. HF. Supplementation of HMTBa increased (P = 0.04) molar proportion of butyrate compared with LF. The addition of IA increased (P < 0.01) molar proportions of branched-chain VFA in the rumen. Milk fat content (3.20 vs. 3.46%; P = 0.04) and yield (0.86 vs. 0.98 kg/d; P < 0.01) decreased for LF vs. HF. The MFD with LF was alleviated by LF-HMTBa and LF-IA; HMTBa increased milk yield (P = 0.03) without altering milk fat content and LF-IA tended to increase (P = 0.08) milk fat content without altering milk yield. However, an interaction for milk fat yield (P < 0.01) was observed between HMTBa and IA, suggesting no additive effect. Moreover, LF-IA decreased (P = 0.03) total preformed fatty acids and increased (P = 0.04) de novo synthesized fatty acids compared with LF treatment. In conclusion, during mild MFD, supplementation of HMTBa or IA alleviated the MFD. However, the alleviation of MFD appeared to be a result of different mechanisms, and no additive effects of the combination were observed on milk fat yield.

Keywords: 2-hydroxy-(4-methylthio) butanoic acid (HMTBa), isoacids, milk fat depression.