Potassium carbonate improves milk quality by enhancing rumen metabolism in Holstein cows

Mid-lactation is a key stage in dairy production characterized by high milk yields and metabolic stress in cows. Dietary potassium carbonate may enhance milk quality, but its response mechanisms, particularly the link between rumen microbiome changes and production performance, remain poorly understood. To address this knowledge gap, a total of 60 multiparous Holstein cows (parity = 2.47 ± 1.06, body weight = 601 ± 25 kg, and days in milk = 127.83 ± 31.91) were divided into four groups (n = 15 cows per group) using a randomized complete block design and fed the corresponding diets for 84 days. The feed treatments were as follows: a control group (CON, basal diet), a low dose group (LD, basal diet + 250 g/d K₂CO₃·1.5H₂O per head), a medium dose group (MD, basal diet + 500 g/d K₂CO₃·1.5H₂O per head), and a high dose group (HD, basal diet + 750 g/d K₂CO₃·1.5H₂O per head). The results showed that potassium carbonate supplementation significantly influenced rumen fermentation patterns, particularly by increasing acetate (P = 0.008) and isovalerate concentrations (P < 0.001). Milk fat (P = 0.004) and protein percentage (P = 0.006) exhibited the most pronounced effects in the MD group. The rumen microbiota and metabolome revealed significant alterations in microbial community structure and function. Notably, the results indicated that in the MD group, there was an increase in the abundance of Kyoto Encyclopedia of Genes and Genomes (KEGG) genes associated with crucial metabolic pathways: amino acid biosynthesis, long-chain fatty acid biosynthesis and fatty acid elongation pathways. These findings suggest that dietary supplementation with 500 g/d of potassium carbonate optimizes milk composition by modulating the rumen microbiota and associated metabolic pathways, supporting the potential for targeted nutritional strategies in dairy management.