[目的]为评估益生菌发酵饲料（PBF）对热应激奶牛的影响。[方法]选取滕州市某奶牛场36 头泌乳中期健康荷斯坦牛,随机分为3 组（每组n=12）：对照组（CON,基础日粮）、低剂量组（L-PBF,2%发酵饲料）和高剂量组（H-PBF,4%发酵饲料）。试验期56 天（含14 天适应期+42 天处理期）。检测采食量（DMI）、产奶量并采集乳样检测乳成分;第0、21、42天采集血浆检测血清CORT、HSP70、TNF-α、IL-6和IL-10;第0、42天采集粪便样品进行qPCR检测乳酸杆菌、双歧杆菌与大肠埃希氏菌丰度。[结果]4%PBF能显著提高直肠粪便中乳酸杆菌和双歧杆菌数量并降低大肠杆菌数量（P<0.05）;显著降低血清CORT、HSP70、TNF-α和IL-6浓度,同时提升IL-10水平（P<0.05）;显著提高DMI、产奶量、乳脂率和乳蛋白率（P<0.05）。[结论]适量添加PBF有助于改善热应激奶牛的肠道微生态与内环境稳定性,从而提升生产表现。

[Objective] To evaluate the effects of probiotic-fermented feed (PBF) on heat-stressed dairy cows.[Method] 36 healthy mid-lactation Holstein cows were selected from a dairy farm in Tengzhou and randomly divided into three groups (n = 12 each): control (CON,basal diet),low-dose (L-PBF,2% fermented feed),and high-dose (H-PBF,4% fermented feed). The trial lasted 56 days,including a 14-day adaptation period and a 42-day treatment period. Dry matter intake (DMI) and milk yield were recorded, and milk samples were collected for composition analysis. Blood samples were collected on days 0,21,and 42 to measure serum cortisol (CORT),heat shock protein 70 (HSP70),tumor necrosis factor-α (TNF-α),interleukin-6 (IL-6),and interleukin-10 (IL-10). Fecal samples were collected on days 0 and 42 for qPCR quantification of Lactobacillus,Bifidobacterium,and Escherichia coli. [Result] Results showed that 4% PBF significantly increased the abundance of Lactobacillus and Bifidobacterium while reducing E. coli in rectal feces (P< 0.05). It also significantly decreased serum levels of CORT,HSP70,TNF-α,and IL-6,while increasing IL-10 (P< 0.05). Additionally,4% PBF significantly improved DMI,milk yield,milk fat percentage,and milk protein percentage (P< 0.05). [Conclusion] Appropriate supplementation of PBF can improve intestinal microecology and internal homeostasis in heat-stressed dairy cows,thereby enhancing productive performance.