Subacute ruminal acidosis (SARA)

SARA describes repeated bouts of low rumen pH that are not severe enough to make a cow visibly ill. A common working definition is rumen pH below about 5.6 for more than three hours a day. It develops when rapidly fermentable carbohydrate is eaten faster than the rumen can absorb and buffer the acids produced.

The signs are seen in the herd rather than in one animal: intake that rises and falls from day to day, depressed milk fat, loose manure with undigested grain, and a rise in lameness some weeks later. Prevention rests on enough physically effective fibre, a gradual step-up to the lactation ration, consistent mixing and feed that is always within reach.

Written for the 2026 edition of the library.