Copelin J E, Firkins J L, Socha M T, Lee C
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691.
Department of Animal Sciences, The Ohio State University, Columbus 43210.
J Dairy Sci. 2021 Feb;104(2):1591-1603. doi: 10.3168/jds.2020-18949. Epub 2020 Dec 11.
The objectives of this experiment were to determine the effects of increased diet fermentability and polyunsaturated fatty acids (FA) with or without supplemental 2-hydroxy-4-(methylthio)-butanoic acid (HMTBa), isoacids (IA; isobutyrate, 2-methylbutyrate, isovalerate, and valerate) or the combination of these on milk fat depression (MFD). Ten Holstein cows (194 ± 58 DIM, 691 ± 69 kg BW, 28 ± 5 kg milk yield) were used in a replicated 5 × 5 Latin square design. Treatments included a high-forage control diet (HF-C), a low-forage control diet (LF-C) causing MFD by increasing starch and decreasing neutral detergent fiber (NDF), the LF-C diet supplemented with HMTBa at 0.11% (28 g/d), the LF-C diet supplemented with IA at 0.24% of dietary dry matter (60 g/d), and the LF-C diet supplemented with HMTBa and IA. Preplanned contrasts were used to compare HF-C versus LF-C and to examine the main effects of HMTBa or IA and their interactions within the LF diets. Dry matter intake was greater for LF-C versus HF-C, but milk yield remained unchanged. The LF-C diet decreased milk fat yield (0.87 vs. 0.98 kg/d) but increased protein yield compared with HF-C. As a result, energy-corrected milk was lower (28.5 vs. 29.6 kg/d) for LF-C versus HF-C. Although the concentration of total de novo synthesized FA in milk fat was not affected, some short- and medium-chain FA were lower for LF-C versus HF-C, but the concentrations of C18 trans-10 isomers were not different. Total-tract NDF apparent digestibility was numerically lower (42.4 vs. 45.6%) for LF-C versus HF-C. As the main effects, the decrease in milk fat yield observed in LF-C was alleviated by supplementation of HMTBa through increasing milk yield without altering milk fat content and by IA through increasing milk fat content without altering milk yield so that HMTBa or IA, as the main effects, increased milk fat yield within the LF diets. However, interactions for milk fat yield and ECM were observed between HMTBa and IA, suggesting no additive effect when used in combination. Minimal changes were found on milk FA profile when HMTBa was provided. However, de novo synthesized FA increased for IA supplementation. We detected no main effect of HMTBa, IA, and interaction between those on total-tract NDF digestibility. In conclusion, the addition of HMTBa and IA to a low-forage and high-starch diet alleviated moderate MFD. Although the mechanism by which MFD was alleviated was different between HMTBa and IA, no additive effects of the combination were observed on milk fat yield and ECM.
本试验旨在确定提高日粮可发酵性和多不饱和脂肪酸（FA），以及添加或不添加2-羟基-4-（甲硫基）-丁酸（HMTBa）、异酸（IA；异丁酸、2-甲基丁酸、异戊酸和戊酸）或二者组合对乳脂率下降（MFD）的影响。选用10头荷斯坦奶牛（泌乳天数194±58天，体重691±69千克，日产奶量28±5千克），采用重复5×5拉丁方设计。处理包括高粗饲料对照日粮（HF-C）、通过增加淀粉和降低中性洗涤纤维（NDF）导致乳脂率下降的低粗饲料对照日粮（LF-C）、添加0.11%（28克/天）HMTBa的LF-C日粮、添加占日粮干物质0.24%（60克/天）IA的LF-C日粮，以及添加HMTBa和IA的LF-C日粮。采用预先计划的对比来比较HF-C和LF-C，并研究HMTBa或IA在LF日粮中的主要作用及其相互作用。与HF-C相比，LF-C的干物质采食量更高，但产奶量保持不变。与HF-C相比，LF-C日粮降低了乳脂产量（0.87对0.98千克/天），但提高了蛋白质产量。因此，LF-C的能量校正乳低于HF-C（28.5对29.6千克/天）。尽管乳脂中从头合成的总FA浓度不受影响，但与HF-C相比，LF-C的一些短链和中链FA含量较低，但C18反式-10异构体的浓度没有差异。与HF-C相比，LF-C的全消化道NDF表观消化率在数值上较低（42.4对45.6%）。作为主要作用，在LF-C中观察到的乳脂产量下降通过添加HMTBa得以缓解，HMTBa通过提高产奶量而不改变乳脂含量，添加IA则通过提高乳脂含量而不改变产奶量，因此作为主要作用，HMTBa或IA提高了LF日粮中的乳脂产量。然而，在HMTBa和IA之间观察到了乳脂产量和能量校正乳的相互作用，表明二者联合使用时没有相加效应。添加HMTBa时，乳脂肪酸谱变化极小。然而，添加IA后从头合成的FA增加。我们未检测到HMTBa、IA及其相互作用对全消化道NDF消化率的主要影响。总之，在低粗饲料和高淀粉日粮中添加HMTBa和IA可缓解中度乳脂率下降。尽管HMTBa和IA缓解乳脂率下降的机制不同，但二者组合对乳脂产量和能量校正乳没有相加效应。
