Urrutia Natalie L, Harvatine Kevin J
Department of Animal Science, Penn State University, University Park, PA.
Department of Animal Science, Penn State University, University Park, PA
J Nutr. 2017 May;147(5):763-769. doi: 10.3945/jn.116.245001. Epub 2017 Mar 22.
Acetate is a short-chain fatty acid (FA) that is especially important to cows because it is the major substrate for de novo FA synthesis. However, the effect of acetate supply on mammary lipid synthesis is not clear. The objective of this experiment was to determine the effect of increasing acetate supply on milk fat synthesis in lactating dairy cows. Six multiparous lactating Holstein cows were randomly assigned to treatments in a replicated design to investigate the effect of acetate supply on milk fat synthesis. Treatments were 0 (control), 5, 10, and 15 mol acetate/d continuously infused into the rumen for 4 d. Rumen short-chain FAs, plasma hormones and metabolites, milk fat concentration, and milk FA profile were analyzed on day 4 of each treatment. Polynomial contrasts were used to test the linear and quadratic effects of increasing acetate supply. Acetate increased milk fat yield quadratically ( < 0.01) by 7%, 16%, and 14% and increased milk fat concentration linearly ( < 0.001) by 6%, 9%, and 11% for 5, 10, and 15 mol acetate/d, respectively, compared with the control treatment. Increased milk fat yield predominantly was due to a linear increase in 16-carbon FAs ( < 0.001) and a quadratic increase in de novo synthesized FAs (<16-carbon FAs; < 0.01), indicating that there was stimulation of de novo synthesis pathways. Apparent transfer of acetate to milk fat was 33.4%, 36.2%, and 20.6% for 5, 10, and 15 mol/d, respectively. Acetate infusion linearly increased the relative concentration of rumen acetate ( < 0.001) before feeding, but not after feeding. Acetate linearly increased plasma ß-hydroxybutyric acid by 29%, 50%, and 78%, respectively, after feeding compared with the control treatment ( < 0.01). Increasing acetate supply to lactating cows increases milk fat synthesis, suggesting that nutritional strategies that increase ruminal acetate absorption would be expected to increase milk fat by increasing de novo FA synthesis.
乙酸盐是一种短链脂肪酸（FA），对奶牛尤为重要，因为它是从头合成脂肪酸的主要底物。然而，乙酸盐供应对乳腺脂质合成的影响尚不清楚。本实验的目的是确定增加乙酸盐供应对泌乳奶牛乳脂肪合成的影响。六头经产泌乳荷斯坦奶牛被随机分配到各处理组，采用重复设计来研究乙酸盐供应对乳脂肪合成的影响。处理组分别为向瘤胃连续灌注0（对照）、5、10和15摩尔乙酸盐/天，持续4天。在每个处理的第4天分析瘤胃短链脂肪酸、血浆激素和代谢物、乳脂肪浓度以及乳脂肪酸谱。采用多项式对比检验增加乙酸盐供应的线性和二次效应。与对照处理相比，对于5、10和15摩尔乙酸盐/天，乙酸盐分别使乳脂肪产量呈二次方增加（P<0.01）7%、16%和14%，使乳脂肪浓度呈线性增加（P<0.001）6%、9%和11%。乳脂肪产量增加主要归因于16碳脂肪酸呈线性增加（P<0.001）以及从头合成脂肪酸（<16碳脂肪酸）呈二次方增加（P<0.01），表明从头合成途径受到刺激。对于5、10和15摩尔/天，乙酸盐向乳脂肪的表观转移率分别为33.4%、36.2%和20.6%。乙酸盐灌注使采食前瘤胃乙酸盐的相对浓度呈线性增加（P<0.001），但采食后未增加。与对照处理相比，采食后乙酸盐使血浆β-羟基丁酸分别线性增加29%、50%和78%（P<0.01）。增加泌乳奶牛的乙酸盐供应会增加乳脂肪合成，这表明增加瘤胃乙酸盐吸收的营养策略有望通过增加从头脂肪酸合成来提高乳脂肪含量。
