We aimed to determine the effects of dietary supplementation with galacto-oligosaccharides (GOS) on the growth performance, serum parameters, and the rumen microbial colonization and fermentation of pre-weaning dairy calves. The study comprised 2 phases of 28 and 42 d, respectively. During phase 1, 24 newborn female Holstein dairy calves were randomly allocated to consume a diet supplemented with 10 g/d GOS (GOS, n = 12) or not (CON, n = 12). Thereafter, during phase 2, the GOS group was further divided into 2 groups: one that continued to consume GOS (GOSC, n = 6) and one that no longer consumed GOS (GOSS, n = 6), alongside the CON group. Galacto-oligosaccharides increased the average daily gain (ADG), body weight, feed efficiency, and serum high-density lipoprotein-cholesterol concentration of dairy calves during phase 1 (P < 0.05). Supplementation with GOS for the entire study reduced the incidence of diarrhea and increased the serum total protein and Ca concentrations (P < 0.05) compared with the CON group. The effect of GOS supplementation persisted after it was stopped because the ADG and final body weight of the GOSS group were higher than those of the CON group (P < 0.05). Furthermore, the GOSS group showed a persistently lower incidence of diarrhea and greater colonization of the rumen with probiotics, at the expense of less beneficial bacteria, which would promote ruminal fermentation and microbial protein synthesis. These findings provide a theoretical basis for the rational application of prebiotics and have important practical implications for the design of early life dietary interventions in dairy calf rearing.

我们旨在确定日粮中添加低聚半乳糖 (GOS) 对断奶前小牛的生长性能、血清参数以及瘤胃微生物定植和发酵的影响。该研究包括两个阶段，分别为 28 天和 42 天。在第 1 阶段，24 头新生雌性荷斯坦奶牛犊被随机分配到食用添加 10 g/d GOS（GOS，n  = 12）或不添加（CON，n  = 12）的饮食。此后，在第 2 阶段，GOS 组进一步分为 2 组：一组继续消耗 GOS（GOSC，n  = 6），另一组不再消耗 GOS（GOSS，n = 6)，与 CON 组一起。低聚半乳糖增加了第一阶段奶牛的平均日增重（ADG）、体重、饲料转化率和血清高密度脂蛋白胆固醇浓度（P  < 0.05）。 与 CON 组相比，在整个研究中补充 GOS 降低了腹泻的发生率，增加了血清总蛋白和 Ca 浓度（P < 0.05）。由于 GOSS 组的 ADG 和最终体重高于 CON 组（P < 0.05)。此外，GOSS 组显示出腹泻发生率持续较低，并且益生菌在瘤胃中的定植率更高，但以较少有益细菌为代价，这将促进瘤胃发酵和微生物蛋白质合成。这些发现为益生元的合理应用提供了理论基础，对奶牛饲养中早期饮食干预的设计具有重要的实践意义。