Department of Animal Science, Penn State University, University Park 16802.
Novus International Inc., St. Charles, MO 63304.
J Dairy Sci. 2019 Jul;102(7):6157-6166. doi: 10.3168/jds.2018-15031. Epub 2019 May 2.
2-Hydroxy-4-(methylthio)butanoate (HMTBa) is a methionine analog that has been observed to attenuate biohydrogenation (BH)-induced milk fat depression (MFD), possibly through reducing the shift to altered BH pathways. It has also been suggested that HMTBa increases microbial protein synthesis in the rumen. Our objectives were to stimulate BH-induced MFD and (1) verify HMTBa inhibition of BH-induced MFD and changes in milk fatty acids (FA) associated with altered rumen BH (i.e., trans-10 C18:1); and (2) determine the effect of HMTBa on milk fat (i.e., odd- and branched-chain FA) and urine biomarkers related to microbial N flow. Twenty-four multiparous cows (45.6 ± 8.5 kg of milk/d; mean ± standard deviation) and 12 primiparous cows (32.8 ± 3.1 kg of milk/d) were arranged in a crossover design. Treatments were unsupplemented control and HMTBa fed at 0.1% of diet dry matter intake. The experiment was 80 d and included a 10-d pretrial covariate period. Each experimental period included 2 phases that differed in risk for BH-induced MFD, including a 28-d low-risk phase (31.6% neutral detergent fiber, 21.8% starch, and no oil) and a 7-d moderate-risk phase (28.7% neutral detergent fiber, 28.1% starch, and 1.0% soybean oil). We found no interaction of treatment and parity. Milk fat yield (1.43 ± 0.51 kg/d) and milk fat trans-10 C18:1 (0.42 ± 0.08 g/100 g of FA) did not differ between treatments during the low-risk phase. However, during the moderate-risk phase, HMTBa maintained higher milk fat concentration (3.91 vs. 3.79%), tended to maintain higher milk fat yield (1.44 vs. 1.38 kg/d), and decreased milk fat trans-10 C18:1 (0.61 vs. 0.93% FA) compared with control. Additionally, HMTBa increased milk fat concentration and secretion of odd- and branched-chain FA by 5.3 and 10.2%, respectively, but urinary biomarkers of microbial N flow (i.e., purine derivatives) did not differ between treatments. However, rumen bacterial samples were not available to provide cow- or treatment-specific microbial protein-to-marker ratios, which is a critical source of variation. Additionally, transfer of odd- and branched-chain FA to milk is dependent on several factors that may affect interpretation of these biomarkers. In conclusion, HMTBa decreased absorption of alternate BH intermediates and maintained higher milk fat when feeding a diet with moderate-risk for MFD.
2-羟基-4-(甲硫基)丁酸 (HMTBa) 是一种蛋氨酸类似物，已被观察到可减轻生物氢化 (BH) 引起的乳脂降低 (MFD)，可能是通过减少向改变的 BH 途径的转变来实现的。也有人提出 HMTBa 增加了瘤胃中微生物蛋白质的合成。我们的目的是刺激 BH 诱导的 MFD，并 (1) 验证 HMTBa 抑制 BH 诱导的 MFD 以及与改变的瘤胃 BH (即反式-10 C18:1) 相关的乳脂肪酸 (FA) 的变化；和 (2) 确定 HMTBa 对乳脂 (即奇数和支链 FA) 和与微生物 N 流相关的尿液生物标志物的影响。24 头经产奶牛（45.6 ± 8.5 kg/d；平均值 ± 标准偏差）和 12 头初产奶牛（32.8 ± 3.1 kg/d）以交叉设计排列。处理组为未补充对照和 HMTBa 以日粮干物质摄入量的 0.1% 喂养。实验持续 80 天，包括 10 天的预试验协变量期。每个实验期包括 2 个不同 BH 诱导 MFD 风险的阶段，包括 28 天的低风险阶段（中性洗涤剂纤维 31.6%、淀粉 21.8%、无油）和 7 天的中风险阶段（中性洗涤剂纤维 28.7%、淀粉 28.1%、1.0%大豆油）。我们没有发现处理和胎次之间的相互作用。在低风险阶段，处理组之间的乳脂产量（1.43 ± 0.51 kg/d）和乳脂反式-10 C18:1（0.42 ± 0.08 g/100 g FA）没有差异。然而，在中风险阶段，HMTBa 维持较高的乳脂浓度（3.91 比 3.79%），倾向于维持较高的乳脂产量（1.44 比 1.38 kg/d），并降低乳脂反式-10 C18:1（0.61 比 0.93% FA）与对照组相比。此外，HMTBa 分别增加了 5.3%和 10.2%的乳脂浓度和奇数和支链 FA 的分泌，但微生物 N 流的尿液生物标志物（即嘌呤衍生物）在处理组之间没有差异。然而，没有获得瘤胃细菌样本，无法提供牛或处理特异性的微生物蛋白与标记物比率，这是变异的关键来源。此外，奇数和支链 FA 向乳中的转移取决于几个可能影响这些生物标志物解释的因素。总之，当饲喂具有中度 MFD 风险的日粮时，HMTBa 减少了替代 BH 中间体的吸收，并维持了较高的乳脂。
