Department of Animal Biosciences, University of Guelph, Guelph, ON, Canada N1G 2W1.
Trouw Nutrition R&D, PO Box 299, 3800 AG, Amersfoort, the Netherlands.
J Dairy Sci. 2021 May;104(5):5432-5444. doi: 10.3168/jds.2020-19485. Epub 2021 Mar 6.
Compared with Holstein whole milk, commercial milk replacers (MR) for calves deliver relatively high levels of lactose and low levels of fat, and protein levels are rather comparable, resulting in a lower energy density and energy-to-protein ratio of the diet. Thus, the objective of this study was to determine the effects of partially exchanging lactose with fat in MR on voluntary feed intake, growth performance, and feeding behavior. Thirty-two male Holstein calves (2.1 ± 0.16 d of age, 46.4 ± 0.77 kg of body weight; BW) were assigned to 16 blocks of 2 calves per block based on arrival date and serum IgG. Within each block, calves were randomly assigned to 2 treatments: a high-lactose MR (HL; 17% fat; 44% lactose), or a high-fat MR (HF; 23% fat; 37% lactose). Lactose was exchanged by fat on a weight per weight basis, resulting in a 6% difference in metabolizable energy density per kilogram of MR. The experiment was divided into 3 phases: preweaning (P1; 0-35 d), weaning (P2; 36-56 d), and postweaning (P3; 57-84 d). For the first 2 wk of P1, calves were individually housed, fed their respective MR ad libitum through teat buckets, and provided access to water. At 14.2 ± 0.5 d of age, calves were group-housed (4 blocks/pen, 8 calves) and housed in group pens for the remainder of the study. In the group pens, calves were fed ad libitum MR, starter feed, chopped wheat straw, and water via automated feeders. During P2, calves were gradually weaned until complete milk withdrawal by 57 d and then monitored until 84 d (P3). Measurements included daily intakes and feeding behavior (rewarded and unrewarded visits), weekly BW and body measurements, and biweekly blood samples. Increasing fat content at the expense of lactose decreased MR intake during P1 by 15% (HL = 1.32 ± 0.04; HF = 1.17 ± 0.04 kg of dry matter per day), whereas total starter intake was not affected by MR composition. Once MR was restricted during P2, HL calves were reported to have more unrewarded visits to the automatic milk feeder than HF calves (11.9 ± 0.95 vs. 8.4 ± 1.03 visits/d, respectively). Crude protein intake was higher for HL calves during P1 (352.1 ± 11.2 vs. 319.6 ± 11.6 g/d), which was attributed to the higher intake of MR during that period, and metabolizable energy intake and protein-to-energy ratio remained comparable between treatments. Plasma cholesterol and nonesterified fatty acids levels were higher in HF calves as a consequence of the diet. Nevertheless, final BW (84 d) did not differ between treatments. Overall, calves fed ad libitum seemed to regulate their intake of MR based on its energy density, without significant effects on solid feed intake and overall growth.
与荷斯坦全脂牛奶相比，商业代乳粉（MR）为犊牛提供相对较高的乳糖和较低的脂肪水平，而蛋白质水平相当，导致饮食的能量密度和能量-蛋白质比降低。因此，本研究的目的是确定部分用脂肪替代 MR 中的乳糖对自愿采食量、生长性能和采食行为的影响。32 头雄性荷斯坦犊牛（2.1±0.16 日龄，46.4±0.77kg 体重；BW）根据到达日期和血清 IgG 分为 16 个 2 头/块的块，每个块内的犊牛随机分配到 2 种处理中：高乳糖 MR（HL；17%脂肪；44%乳糖）或高脂肪 MR（HF；23%脂肪；37%乳糖）。以重量为基础交换乳糖中的脂肪，导致每千克 MR 的代谢能密度差异为 6%。实验分为 3 个阶段：哺乳期前（P1；0-35 天）、断奶期（P2；36-56 天）和断奶后（P3；57-84 天）。在 P1 的前 2 周，犊牛单独饲养，通过奶嘴桶自由采食各自的 MR，并提供水。在 14.2±0.5 日龄时，犊牛被分组饲养（4 个块/栏，8 头），并在研究剩余期间被饲养在组栏中。在组栏中，犊牛通过自动饲养器自由采食 MR、起始饲料、切碎的小麦秸秆和水。在 P2 期间，犊牛逐渐断奶，直到 57 天完全断奶，然后监测至 84 天（P3）。测量包括每日摄入量和采食行为（有报酬和无报酬访问）、每周 BW 和体尺以及每两周一次的血液样本。以脂肪代替乳糖会降低 MR 的摄入量，哺乳期前 15%（HL=1.32±0.04；HF=1.17±0.04kg 干物质/天），而 MR 组成不会影响总起始饲料的摄入量。一旦 P2 期间限制了 MR 的摄入量，HL 犊牛的无报酬访问自动牛奶饲喂器的次数比 HF 犊牛多（11.9±0.95 比 8.4±1.03 次/天）。HL 犊牛在 P1 期间的粗蛋白摄入量较高（352.1±11.2 比 319.6±11.6g/d），这归因于该期间对 MR 的摄入量较高，而代谢能摄入量和蛋白质-能量比在处理之间保持可比。HF 犊牛的血浆胆固醇和非酯化脂肪酸水平较高，这是由于饮食所致。然而，最终 BW（84 天）在处理之间没有差异。总体而言，自由采食的犊牛似乎根据 MR 的能量密度调节其摄入量，而对固体饲料摄入量和整体生长没有显著影响。
