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The normal range for rumen pH is 6.5 to 7.0. When pH drops below this optimal range the animal’s health and productivity suffer. Acidosis occurs at pH 5.5 and below. The rumen stops contracting and appetite drops off. The increase in acidity inhibits lactic acid-utilizing bacteria and encourages lactic acid-producing bacteria, driving the pH even lower.
Signs of sub-acute acidosis include: reduced milk yield or milk fat, reduced appetite, reduced cud-chewing, diarrhea, sore hooves, and laminitis. If the problem persists, acute acidosis can develop. Acid can eventually damage the papillae in the rumen, decreasing feed efficiency and productivity. If pH drops low enough, acid can be absorbed through the rumen wall, leading to metabolic acidosis, which can cause shock or death.
Acidosis can be caused by high energy diets that include too many fermentable carbohydrates. Lactic acid-producing bacteria thrive on these compounds and stimulating their growth drives the microbial community out of balance.
The rumen can be stabilized by reducing fermentable carbohydrates (concentrates) and adding long fiber to the diet. Long fiber encourages cudding, which increases saliva output. Saliva acts as a buffer, making shifts in rumen pH less likely. Cow comfort is also important because a comfortable cow is more likely to lie down and ruminate.