Effects on rumen pH and feed intake of a dietary concentrate challenge in cows fed rations containing pH modulators with different neutralizing capacity
Based on Bach et al., 2023; Journal of Dairy Science, 2023
Introduction
High-concentrate diets induce rumen pH depression and disrupt the rumen microbiota, particularly fibrolytic bacteria such as Fibrobacter, which are highly sensitive to acidic conditions.
Stabilizing rumen pH is therefore essential to maintain microbial balance and fiber degradation capacity.
The present study evaluated the effects of pH modulators with different neutralizing capacities under an induced acidosis challenge.
The study focused on rumen pH dynamics, time under subacute acidosis (pH < 5.8), and rumen microbiota, with a specific focus on fibrolytic populations.
Material and methods
Forty-five lactating dairy cows were assigned to three treatments:
- CON: Control diet without supplementation.
- SB: Diet supplemented with sodium bicarbonate at 0.82% of DM, approximately 200 g/cow/day.
- MG: Diet supplemented with a magnesium-based blend, pHix-up, at 0.25% of DM, approximately 62 g/cow/day.
Diets were formulated to provide similar theoretical neutralizing capacity. A progressive dietary challenge was applied by decreasing the forage-to-concentrate ratio from 48:52 to 36:64 to induce rumen pH depression.
Rumen pH was continuously monitored, and microbiota composition was assessed using long-read sequencing.
Results and discussion
Rumen pH decreased as the proportion of concentrate increased across all treatments. However, with the acidosis challenge, cows supplemented with pHix-up maintained a higher rumen pH compared to both control and sodium bicarbonate treatments.
Cows receiving pHix-up also exhibited a reduced duration of time below pH 5.8. These results indicate a more sustained buffering effect throughout the day compared to the rapid but transient action of sodium bicarbonate.
Despite similar theoretical neutralizing capacity, pHix-up provided a more progressive and sustained stabilization of rumen pH than sodium bicarbonate.
Microbiota analysis revealed that supplementation with pHix-up was associated with higher microbial diversity and lower inter-animal variability, indicating a more stable rumen ecosystem.
In addition, the relative abundance of Fibrobacter, a key fibrolytic genus highly sensitive to low pH conditions, was greater in cows receiving pHix-up compared to those supplemented with sodium bicarbonate.
The improved rumen pH stability observed with pHix-up likely contributed to the preservation of fibrolytic bacteria, supporting fiber degradation capacity and rumen microbiome resilience.
Why fibrolytic bacteria matter
Fibrolytic bacteria are essential for the degradation of structural carbohydrates in the rumen. When rumen pH remains low for prolonged periods, these bacterial populations are inhibited, reducing fiber digestion and compromising rumen function.
By helping maintain a more stable rumen environment, pHix-up supported conditions that favored the preservation of Fibrobacter and other beneficial microbial populations under acidotic stress.
Maintaining fibrolytic bacteria is critical for preserving fiber degradation, feed efficiency, and rumen health in high-concentrate feeding systems.
Conclusions
Supplementation with pHix-up improved rumen pH stability under an acidosis challenge and promoted the preservation of fibrolytic microbiota, particularly Fibrobacter.
These results suggest that pHix-up supports rumen function not only through buffering capacity but also by stabilizing the rumen microbiome and protecting fiber-degrading bacteria under high-concentrate feeding conditions.
pHix-up offers a targeted approach to rumen pH stabilization, helping preserve microbial balance, fiber degradation capacity, and rumen resilience during acidotic challenges.