Acid compositions for ruminants containing a plurality of acid-neutralizing salts with pK.sub.a's effective at different ruminant gastrointestinal pH ranges and an active probiotic culture capable of stimulating the growth and concentration of beneficial acid-consuming rumen microorganisms. Methods for preventing clinical and sub-clinical acidosis in ruminants with the acid-neutralizing salts and feed compositions to which the acid-neutralizing salts have been added are also disclosed.