The rumen is a fermentation chamber designed to convert structural and nonstructural carbohydrates into volatile fatty acids (VFA), which supply most of the cow’s energy. Acetate, propionate, and butyrate are continuously produced by microbial fermentation. These acids are absorbed across the rumen wall, while saliva provides bicarbonate buffering during rumination.
Under stable conditions, acid production and acid removal remain in equilibrium. Acidosis develops when acid production exceeds buffering and absorptive capacity. Rapid fermentation of starches and sugars increases acid load. Insufficient physically effective fiber reduces chewing and saliva secretion. Inadequate microbial adaptation may allow lactic acid to accumulate. Compromised epithelial function may slow absorption. This imbalance, rather than a single pH value, defines ruminal acidosis (Nagaraja and Titgemeyer 2007; Golder and Lean 2024).
Clinical ruminal acidosis
Clinical ruminal acidosis typically follows sudden ingestion of large quantities of highly fermentable carbohydrates. Mixing errors, abrupt ration changes, accidental grain access, or poorly managed step-up programs are common triggers.
In these situations, lactic acid production can rise rapidly, and rumen pH may fall below 5.0. However, the absolute nadir of pH alone does not determine severity. The duration for which ruminal pH remains below critical thresholds is equally, and often more, important. Prolonged exposure to low pH compromises epithelial integrity, impairs absorptive capacity, and promotes proliferation of acid-tolerant, lactate-producing bacteria, amplifying instability.
As pH declines and remains depressed, osmotic pressure increases, drawing fluid into the rumen and contributing to systemic dehydration and metabolic acidosis.
Clinically affected cattle may exhibit depression, decreased rumen motility, watery diarrhea containing undigested grain, weakness, ataxia, and recumbency. Without immediate intervention, mortality may occur. Survivors often face secondary complications such as rumenitis, liver abscesses, laminitis, or pulmonary disorders (Nagaraja and Titgemeyer 2007).
Continue reading this article published in Feed & Additive Magazine.
