Ruminal fermentative parameters and blood acido-basic balance changes during the onset and recovery of induced latent acidosis in sheep

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 H 2 CO 3 and 0.55 for HCO 3 -).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 (HCO 3 -), total CO 2 content (TCO 2 ), 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.acidosis / rumen fermentation / protozoa / blood / acid-base status 513