To evaluate the effects of probiotic-fermented feed (PBF) on heat-stressed dairy cows.

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.

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).

Appropriate supplementation of PBF can improve intestinal microecology and internal homeostasis in heat-stressed dairy cows, thereby enhancing productive performance.