Four ruminal cannulated Texel wethers were used to study the long-term effects of an acidotic diet on ruminal parameters and blood acid-base status. The short-term events around feeding and the recovery of the animals were followed after this nutritional disturbance. Sheep were limit-fed consecutively a control diet H (100% hay) ( one week), an acidotic diet W (60% wheat + 40% hay) ( 2 weeks), and again the control diet ( 2 weeks). Mean, minimum and maximum ruminal pH were lower, and the time and area under pH 6.0 were higher ( P < 0.001) with the W diet than with the H diet. These pH parameters indicate a latent acidosis defined here as a subacute and maintained acidosis. Before feeding, the drop in ruminal pH with the W diet was correlated with an increase in the VFA buffering capacity (BC) (R-2 = 0.70) and with a decrease in the BC of both carbonic acid functions (R-2 = 0.52 for H2CO3 and 0.55 for HCO3-). After feeding, the acidotic diet effect on ruminal pH was not explained by variations in the BC of either of these chemical species. Ruminal lactate concentration was higher with the W diet compared to the H diet (P < 0.001) but remained low(< 2 mmol . L-1). Total VFA concentration ( P < 0.001), acetate ( P < 0.001) and propionate ( P < 0.01) proportions in the rumen decreased with the W diet, while the butyrate proportion increased (P < 0.001). The number of Entodiniomorphs increased with the W diet ( P < 0.001). Most parameters showed no significant variation between the 2 weeks with the W diet ( P > 0.05). All ruminal parameters, except for ammonia, recovered to initial levels during the H diet redistribution ( P < 0.05) while blood parameters decreased (pH, P < 0.05; bicarbonates (HCO3-), total CO2 content (TCO2), base excess in whole blood (Beb) and in extra cellular fluid (Beecf), P < 0.01). This decrease, initiated during the distribution of the acidotic diet, suggests a mobilization of body alkaline reserves and a longer recovery time in blood than in the rumen. We observed a non-lactic but butyric latent acidosis, linked to Entodiniomorph proliferation, suggesting an intermediate stage before the onset of acute lactic acidosis.
