Dos Santos Neto J M, Garver J, de Souza J, VandeHaar M J, Lock A L
Department of Animal Science, Michigan State University, East Lansing, MI 48824.
Department of Animal Science, Michigan State University, East Lansing, MI 48824.
J Dairy Sci. 2025 Apr;108(4):3573-3585. doi: 10.3168/jds.2024-25731. Epub 2025 Jan 7.
The aim of our study was to assess the effects of low- or high-starch diets with or without palmitic acid (C16:0) supplementation on the yield of milk, milk components, and energy partitioning of primiparous and multiparous dairy cows between mid and late lactation. Thirty-two Holstein cows, 12 primiparous (163 ± 33 DIM; mean ± SD) and 20 multiparous (179 ± 37 DIM; mean ± SD), were used in a split-plot Latin square design. Parity was considered the main plot, and within each plot, treatments were then randomly assigned in a replicated 4 × 4 Latin square with 21-d periods and balanced for carryover effects. Treatments were in a 2 × 2 factorial arrangement of dietary starch level and fatty acid (FA) supplementation as main factors. The starch factor comprised either low (LS; 16% of diet DM) or high (HS; 32% of diet DM) dietary starch. Dietary starch was altered by varying the proportion of ground corn, whole cottonseed, and soyhulls, with LS and HS diets containing ∼15% and 18% forage NDF (fNDF) and ∼37% and 25% NDF, respectively. The FA supplementation factor consisted of either control with no FA supplementation (CON) or a C16:0-enriched supplement at 1.5% of diet DM replacing soyhulls (PALM). Compared with LS, HS increased plasma insulin (0.20 μg/L) and energy partitioning to body reserves (2.04 percentage units), tended to increase BCS and BW change, and decreased DMI (1.10 kg/d), milk fat yield (0.04 kg/d), and MUN (2.10 mg/dL). Compared with CON, PALM increased energy output to milk (1.10 Mcal/d) and the yields of milk fat (0.10 kg/d), 3.5% FCM (1.90 kg/d), and ECM (1.60 kg/d), and had no effect on BW-related variables. We observed a 3-way interaction between parity, starch, and FA supplementation affecting multiparous but not primiparous cows, where PALM increased plasma insulin concentration (0.14 μg/L) in LS but had the opposite effect in HS by tending to decrease insulin. Our results demonstrate important interactions between parity, starch levels, and FA supplementation. Overall, feeding a low-starch diet to mid- and late-lactation dairy cows helped prevent excessive body condition and weight gain while increasing milk fat yield compared with a high-starch diet. Multiparous cows may benefit the most from a low-starch diet because multiparous cows seemed more prone to accumulating body reserves. Feeding a C16:0-enriched supplement increased milk fat yield and ECM without increasing weight gain, regardless of starch level or parity.
我们研究的目的是评估在泌乳中期和后期，补充或不补充棕榈酸（C16:0）的低淀粉或高淀粉日粮对初产和经产奶牛的产奶量、乳成分及能量分配的影响。采用裂区拉丁方设计，选用32头荷斯坦奶牛，其中12头初产牛（163±33天泌乳天数；均值±标准差）和20头经产牛（179±37天泌乳天数；均值±标准差）。胎次被视为主区组，在每个主区组内，将处理随机分配到一个重复的4×4拉丁方中，每期21天，并对残留效应进行平衡。处理采用2×2析因设计，以日粮淀粉水平和脂肪酸（FA）补充作为主要因素。淀粉因素包括低（LS；占日粮干物质的16%）或高（HS；占日粮干物质的32%）日粮淀粉。通过改变玉米粉、全棉籽和大豆皮的比例来改变日粮淀粉，LS和HS日粮分别含有约15%和18%的饲草中性洗涤纤维（fNDF）和约37%和25%的中性洗涤纤维。FA补充因素包括不补充FA的对照组（CON）或用占日粮干物质1.5%的富含C16:0的补充剂替代大豆皮（PALM）。与LS相比，HS使血浆胰岛素增加（0.20μg/L），能量分配到体储备增加（2.04个百分点），BCS和体重变化有增加趋势，干物质采食量（DMI）降低（1.10kg/d），乳脂产量降低（0.04kg/d），乳尿素氮（MUN）降低（2.10mg/dL）。与CON相比，PALM使产奶能量输出增加（1.10Mcal/d），乳脂产量（0.10kg/d）、3.5%乳脂校正乳（FCM）产量（1.90kg/d）和能量校正乳（ECM）产量（1.60kg/d）增加，对体重相关变量无影响。我们观察到胎次、淀粉和FA补充之间存在三因素交互作用，影响经产牛而非初产牛，其中PALM使LS组血浆胰岛素浓度增加（0.14μg/L），但在HS组有相反作用，即有降低胰岛素的趋势。我们的结果表明胎次、淀粉水平和FA补充之间存在重要的交互作用。总体而言，与高淀粉日粮相比，给泌乳中期和后期的奶牛饲喂低淀粉日粮有助于防止体况和体重过度增加，同时提高乳脂产量。经产牛可能从低淀粉日粮中获益最多，因为经产牛似乎更容易积累体储备。无论淀粉水平或胎次如何，饲喂富含C16:0的补充剂可提高乳脂产量和ECM，且不增加体重。
