Abstract：
Vegetable fat blends are commonly used as fat sources in milk replacers (MR) for calves, but their composition differs considerably from that of bovine milk fat. The aim of this study was to investigate the serum lipid profile of pre-weaned calves fed twice-daily MR containing 30% fat (% DM). Upon arrival, 30 male Holstein-Friesian calves (BW = 45.6 ± 4.0 kg, age = 2.29 ± 0.8 d) were randomly assigned to 2 experimental diets (n = 15 per treatment): one MR was derived from either vegetable fats (VG; 80% rapeseed and 20% coconut fats) or animal fats (AN; 65% Packer\'s lard and 35% dairy cream). The 2 MR formulas contained 30% fat, 24% CP, and 36% lactose. Calves were housed indoors in individual pens with ad libitum access to chopped straw and water. Daily milk allowances were 6.0 L from d 1 to 5, 7.0 L from d 6 to 9, and 8.0 L from d 10 to 35, divided into 2 equal meals and prepared at 13.5% solids. An untargeted liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) method was employed to analyze the lipid profiles in the serum of calves sampled from the jugular vein at 35 d of age. In total, 594 lipids were characterized, comprising 25 different lipid classes. Principal component analysis (PCA) showed significant separation between VG and AN, indicating different lipid profiles in the serum. An orthogonal partial least squares discriminant analysis (OPLS-DA) classification model was used to further validate the distinction between the 2 treatment groups. The model exhibited a robust class separation and high predictive accuracy. Using a Volcano plot (fold change threshold ≥1.5 and false discovery rate ≤0.05), it was observed that calves fed AN had higher levels of 39 lipid species in serum than calves fed VG, whereas 171 lipid species were lower in the AN group. Lipid classes, such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SM), triglycerides (TG), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE), were different. In particular, PC and PE were observed at lower levels in calves fed AN, possibly indicating shifts in cell membrane characteristics, intracellular signaling, and liver functions. In addition, a decrease in certain triglyceride (TG) species was observed in calves fed AN, including a decrease in TG species such as TG 36:0 and TG 38:0, possibly related to variations in the content of certain fatty acids (FA) within the AN MR, such as C10:0, C12:0, C14:0, and C18:0 compared with the VG MR. Calves fed AN had lower levels of LPC and LPE, and lyso-phosphatidylinositol (LPI), SM, and phosphatidylinositol (PI) species than calves fed VG, suggesting shifts in lipoprotein and lipid metabolic pathways. In conclusion, these results deepen the understanding of how lipid sources in MR can modulate the serum lipidome profiles of dairy calves.
摘要：
植物性脂肪混合物通常用作小牛的牛奶替代品（MR）中的脂肪来源，但是它们的组成与牛乳脂肪有很大不同。这项研究的目的是研究断奶前小牛的血脂状况，每天两次喂养含有30％脂肪（％DM）的MR。抵达后,30只雄性荷斯坦-弗里斯小牛(体重=45.6±4.0公斤，年龄=2.29±0.8d）被随机分配到2种实验饮食中（每种治疗n=15）：一种MR来自植物脂肪（VG；80％油菜籽和20％椰子脂肪）或动物脂肪（AN；65％Packer猪油和35％乳制品奶油）。2个MR配方含有30%的脂肪，24%CP,和36%的乳糖。小牛被关在室内的各个围栏中，可以随意使用切碎的稻草和水。从第1天到第5天，每日牛奶配额为6.0L，从第6天到第9天为7.0L，从第10天到第35天为8.0L，分为2等份，以13.5％的固体含量制备。采用非靶向液相色谱-四极杆飞行时间质谱（LC-QTOF-MS）方法分析了35日龄时从颈静脉采样的小牛血清中的脂质分布。总的来说,594脂质进行了表征，包含25种不同的脂质类别。主成分分析(PCA)显示VG和AN之间有显著的分离，表明血清中不同的脂质分布。采用正交偏最小二乘判别分析(OPLS-DA)分类模型进一步验证2个治疗组之间的区别。该模型表现出稳健的类别分离和高预测精度。使用火山图(倍数变化阈值≥1.5，错误发现率≤0.05)，据观察，饲喂AN的小牛血清中39种脂质的水平高于饲喂VG的小牛，而AN组的171种脂质较低。脂类，如磷脂酰胆碱（PC），磷脂酰乙醇胺(PE),鞘磷脂（SM），甘油三酯（TG），溶血磷脂酰胆碱（LPC），和溶血磷脂酰乙醇胺（LPE），是不同的。特别是,在饲喂AN的小牛中观察到PC和PE水平较低，可能表明细胞膜特征的变化，细胞内信号，和肝功能。此外,在饲喂AN的小牛中观察到某些甘油三酯（TG）物种的减少，包括TG种类的减少，例如TG36：0和TG38：0，可能与ANMR中某些脂肪酸（FA）含量的变化有关，例如C10:0、C12:0、C14:0和C18:0与VGMR相比。饲喂AN的小牛LPC和LPE水平较低，和溶血磷脂酰肌醇（LPI），SM,和磷脂酰肌醇（PI）物种比饲喂VG的小牛，提示脂蛋白和脂质代谢途径的变化。总之,这些结果加深了对MR中的脂质来源如何调节乳牛血清脂质含量的理解。
