Subacute ruminal acidosis or SARA is damaging to fiber digestion and a cow's milk production potential.

In one study, Karen Beauchemin, research scientist with Agriculture and Agri-Food Canada, measured fiber digestion in cows with high ruminal pH and cows with low ruminal pH. Cows with a higher mean pH had a 17 percent difference in neutral detergent fiber digestion compared to cows with lower pH.

"If you put that into your models, this would translate into 3 kilograms (about 6.6 pounds) per day less milk," she said in April at the Tri-State Dairy Nutrition Conference in Fort Wayne, Ind. "The cow is not really sick, but it's not eating to its potential and it's not digesting to its potential."

There also is increasing concern about the impact that SARA has on rumen health. SARA is characterized as a pH value consistently below 5.5.

"That continual low pH has harmful effects on the rumen epithelium," Beauchemin said. It can cause lesions or open sores, which are undesirable because they can allow harmful bacteria, endotoxins, etc., to penetrate the rumen wall.

"Increasingly, there is work to show that this kind of thing is associated with an inflammatory response," she said.

There also is work (particularly in horses) that shows that when these toxins are absorbed into the bloodstream, they cause destruction of the connective tissue in the hoof, which can potentially lead to lameness.