Effects of different doses of potassium bicarbonate on lactation performance, milk fatty acid composition, rumen fermentation, and feed digestibility in peak-lactation dairy cows.

High-starch diets are commonly used to support high milk yields in Holstein dairy cows. Although these diets enhance volatile fatty acid (VFA) production and energy supply, the imbalance between rapidly fermentable carbohydrates and fibre can compromise rumen stability. To mitigate ruminal disturbances under high-starch feeding conditions, dietary supplementation with buffers, regulating rumen-degradable starch, and modulating rumen microbiota through probiotics have been explored to stabilize rumen fermentation. Amongst others, supplementation with sodium- or potassium-based dietary buffers has consistently emerged as one of the most effective interventions for maintaining ruminal pH homeostasis. In the study cited the effects of potassium bicarbonate (KHCO₃) supplementation by increasing dietary K from 1.3% to 1.6% and 1.9% on lactation performance, milk fatty acids (FA), rumen fermentation, nutrient digestibility, and serum metabolites were evaluated. Given that KHCO₃ elevates dietary cation-anion difference (DCAD) and buffering supply, the authors hypothesized that graded KHCO₃ supplementation would enhance fibre digestion and acetate production, thereby altering milk fat yield and fatty acid composition. The results should provide practical guidance for optimizing KHCO₃ use to support rumen function and milk fat synthesis.

Sixty multi-lactation Holstein cows at 69.8 ± 21.2 days in milk and producing 41.2 ± 5.4 kg milk/day were randomly assigned to diets containing 0% (CON), 0.75%, or 1.50% KHCO₃(DM basis) for an 8-week treatment period. The data were analysed using a mixed model with dietary treatment, time, and their interaction as fixed effects and cow as a random effect. Linear and quadratic responses were assessed using pre-planned contrasts.

The diets supplemented with KHCO₃had no effect on dry matter intake (DMI) and milk yield. However, 3.5% fat-corrected milk (FCM) tended to increase linearly, milk fat concentration increased linearly, and FCM/DMI exhibited linear and quadratic increases with increasing KHCO₃supplementation. Apparent digestibility of the fibre fractions NDF and ADF increased linearly, accompanied by a linear increase in the molar proportion of acetate with increasing KHCO₃. In contrast, total volatile fatty acid (VFA) concentration exhibited a quadratic response. Ruminal pH exhibited a quadratic increase with increasing

KHCO₃addition, whereas ruminal ammonia-N and the molar proportions of butyrate, valerate, and iso-valerate showed linear and quadratic decreases. Blood urea nitrogen concentration decreased linearly, with no effects on serum indicators of energy metabolism, liver function, or antioxidant capacity. Milk concentrations of C10:0, C12:0, and cis-9, trans-11 CLA increased linearly, whereas the trans-10 to trans-11 C18:1 ratio decreased linearly with increasing KHCO₃supplementation. Overall, supplementation with KHCO₃during peak lactation improved fibre digestibility and favoured trans-11 bio-hydrogenation, thereby improving milk fat content and feed efficiency.

Conclusions: Supplementing with KHCO₃ did not affect DMI or milk yield but linearly increased milk fat concentration compared with the control. KHCO₃ supplementation also linearly improved fibre digestibility and the molar proportion of ruminal acetate, and resulted in a higher ruminal pH relative to control. Ruminal NH3-N and BUN concentrations decreased linearly in cows fed KHCO₃ compared with the control, indicating improved nitrogen-use efficiency. In addition, KHCO₃ supplementation increased the milk concentration of cis-9, trans-11 CLA and decreased the trans-10 to trans-11 C18:1 ratio, suggesting a shift in ruminal bio-hydrogenation toward the trans-11 path-way, a pattern linked to reduced milk fat depression risk. The similar responses observed between the 0.75% and 1.50% inclusion levels suggest that moderate supplementation (0.75% of DM) should be sufficient to achieve most of the beneficial effects shown in the study.