An evaluation of parameters for the detection of subclinical rumen acidosis in dairy herds.

An observational study was conducted in six Danish dairy herds. A specially designed stomach tube was compared to the rumenocentesis technique as part of the monitoring of rumen pH. In contrast to a previous study, the use of the stomach tube appeared to reduce saliva contamination. However, correlation with the rumenocentesis technique was poor ( r = 0.33; p = 0.019) and a linear model could only partly explain variations between either results. The presence of subclinical rumen acidosis (SRA) was evidenced in one herd only, as judged by results obtained by the rumenocentesis technique. The present study revealed some limitations of the rumenocentesis technique in small or medium-sized herds due to difficulties in selecting sufficient numbers of cows in the respective groups at risk. The finding of two apparently clinical normal cows with rumen pH values below 5.0 leads to the consideration that such fluctuations may be temporary and at least does not give rise to clinical symptoms. However, the long-term effect of such fluctuations is not known. In general, primiparous cows seemed more prone to low ruminal pH values (< 6.0), higher ruminal concentrations of short-chain fatty acids, and possibly to metabolic acidosis, than were multiparous cows. Ruminal propionate was the most precise predictor of rumen pH, whereas milk fat percentage varied greatly between lactational groups. Blood lactate dehydrogenase (LDH), beta-hydroxybutyrate (BHB) and fructosamine as well as urine phosphorus excretion and renal net acid-base excretion (NABE) were related to ruminal acid load, but were not predictive of rumen pH. Monitoring of dairy herds for SRA should be performed routinely and employ several diagnostic tools (rumenocentesis, renal NABE determination) as well as specific knowledge of herd management and feeding routines.