Subacute ruminal acidosis (SARA) has been considered as a major metabolic disease in high producing dairy herds for years. However, different feeding practices However, different feeding practices and herd’s production levels are found in Wallonia. SARA prevalence in local herds was thus required 174 cows (164 Holstein and 10 Brown Swiss) out of 24 walloon herds were sampled from 2011 to 2012 for evaluation of their ruminal function. Selection of minimum 5 cows per herd was made on basis of days in milk (<150 DIM), or low milk fat % (F <3.2%), or fat/protein % (F/P≤1), or at farmer’s request (animal debilitated or chronically ill). Ruminal fluid was sampled 4-8 h after feeding using a Geishauser oro-pharyngeal probe, preventing saliva contamination. pH was measured by a portable pHmeter and values were reduced by 0.35 as proposed by Duffield (2004) because of the higher pH values in reticulum sampling site compared with rumenocentesis. Redox potential was determined by Methylene Blue Reduction Time (MBRT) and protozoa assessed by microscopy. Production values were obtained by the National Dairy Herds Improvement. Health scores were determined as described by Zaaier et al. (2001). RESULTS Mean production values ± SD of these animals (DIM: 106 ± 84) were 33.2 ± 8.9 kg milk, F = 3.47 ± 0.72%, P = 3.25 ± 0.25%, F/P = 1.07 ± 0.23. Mean BCS was 2.6 ± 0.6. Mean pH value ± SD was 6.50 ± 0.42. 10 animals (5.7%) from 6 herds were below 5.8, of which 4 cows from H8 (23 sampled cows). No result was < 5.5. MBRT was 4.16 ± 3.13 min. In 5 cows, value < 1min indicated a more amylolytic bacterial flora. In 24 samples, no reduction of MB occurred, demonstrating bacterial inactivity. Disappearance of large protozoa was observed in 6 samples, of which 5 abnormal specimens came from H8. No correlation between low pH values and F/P or %F could be found. CONCLUSION In no herd, prevalence was >25%, required for SARA diagnosis. Regarding these results, prevalence of SARA appears very low in Wallonia while on the opposite, ...