Can a single rumen sample really diagnose SARA in commercial farms

The accuracy of diagnosis of subacute rumen acidosis (SARA) with a single measurement of the ruminal pH remains contradictory. To clarify this aspect, a large assessment of rumen, faecal and blood parameters was performed in several herds characterised by diets rich in non-structural carbohydrates. Rumen fluid was collected by rumenocentesis 6 h after feeding from 114 dairy cows (half 30–90 and half 150–250 days in milk) from 10 herds. In the same day, blood and faecal samples were collected and milk yield was recorded. The herds were ex-post classified as healthy (CTR n = 6) or as at risk for SARA (n = 4), based on ruminal pH. SARA versus CTR herds had lower rumen pH (5.67 vs 5.97 P < 0.01) and higher concentration of VFA, with lower acetate (P < 0.01) and higher propionate and valerate (P < 0.05) proportions. Moreover, the faecal DM was lower (P < 0.05), whereas the milk yield was higher with a lower concentration of fat (P < 0.05). At blood level, no significant differences were observed between the groups on positive acute-phase proteins, whereas SARA herds showed higher concentrations of paraoxonase and Ca and lower of cholesterol, total proteins, nitrates, Na and Zn (P < 0.01). Therefore, SARA herds did not show any evident symptom of ruminal disorder or systemic inflammation. On the contrary, these herds had a higher milk yield and a better inflammometabolic profile. These data confirm the difficulties to diagnose the SARA by a single measurement of ruminal pH in commercial herds and suggest the need of more specific indices to identify herds at risk.