CO2 holdup monitoring, ruminal acidosis might be caused by CO2 poisoning

Abstract

Ruminal CO2 holdup or high dissolved CO2 concentrations (dCO2) for long postprandial periods might increase CO2 absorption and the risk of CO2 poisoning. Ruminal pH and dCO2 are intertwined, explaining why ruminal acidosis is ascribed to low ruminal pH, which is a spurious relationship. Here, the use of an ATR-IR spectrometer to monitor ruminal dCO2 is described. Three fistulated lactating dairy cattle were exposed to diets tailored to increase both dCO2 and the risk of subacute ruminal acidosis (SARA). Indwelling pH sensors and ruminal fluid samples were used as references, and a categorical analysis based on the Gaussian distribution of the ruminal dCO2 was applied to detect CO2 holdup. The milk yield, milk components and feed intake supported a positive role for high dCO2 on rumen function. However, SARA was associated with CO2 holdup, viz. sustaining critical ruminal dCO2 for extended postprandial periods. Therefore, SARA was most likely a sign of CO2 poisoning rather than a pH decline. Monitoring ruminal dCO2 with the proposed categorical analysis might help us to optimise rumen function and reduce the risk of ruminal acidosis.