What is the primary pH change and consequence after a sudden high-concentrate diet leading to ruminal acidosis?

• A. pH drops below 5.5 with lactic acid buildup causing decreased motility and dehydration.
• B. pH rises above 7.0 due to buffering capacity.
• C. pH remains stable around 6.8 with normal motility.
• D. pH falls to 4.0 with no systemic signs.

Answer: (C)

Sudden high-concentrate feeding drives rapid fermentation of easily fermentable carbohydrates in the rumen, producing large amounts of acids, especially lactic acid. This acid load overwhelms the rumen’s buffering capacity, causing a notable drop in pH. Normal rumen pH is around 6.2–6.8; when acidosis develops, pH falls below 5.5 and can go even lower in severe cases. The falling pH slows or inhibits rumen motility and fiber digestion, and the buildup of lactic acid promotes dehydration and electrolyte disturbances. If the acidosis is marked, it can lead to systemic effects and complications such as laminitis. So the hallmark is a decrease in pH with acid buildup and reduced motility, not a stable pH around 6.8.