What is ruminal CO2 Holdup?

The simplest example is to observe CO2 holdup in beer, like the rumen fluid, beer is a non-ideal solution. Observed dissolved CO2 coming out of the solution in the small columns of gas CO2 bubbles rising up from the bottom to the top of the glass. You can compare this effect with an ideal solution like in a glass of carbonated water, in here the CO2 bubbles are bigger and they are released faster.

On ideal fluids dCO2 concentrations mirror the CO2 partial pressure on the top, so quickly the two medium equate (Henry´s law). On non-ideal solutions dCO2 cannot escape easily and dCO2 concentrations are greater within the fluid than on the top, slower equilibrium.

You can change the physicochemical properties of carbonated water by adding soap, which changes the fluid’s surface tension (stir gently). The CO2 gas bubbles rising up in the column of the carbonated water-soap glass will become smaller. This is the same effect that feeding has on the rumen fluid, the physicochemical characteristics of the diets will help either to release CO2 or trap it (CO2 holdup).

Once CO2 holdup is established a large amount of ruminal dCO2 can be found in the ruminal fluid which might lead to CO2 poisoning (SARA): dizziness, rapid breathing, heart rate increase, confusion, apathy and recumbency. However, any physicochemical factor that alters CO2 holdup might produce fast release of the trapped dCO2, i.e. the fluid will go from a non-ideal solution to an ideal solution, with the concomitant formation of frothy foam on the top. This is the mechanism of bloat and abomasal dysplasia.

We can simulate these effects in our benchtop experiment. Add table salt or baking soda to now the 3 glasses (stir gently). The effect of the salts on the fluids is to help in the formation and release of CO2 bubbles (nucleation). The fast release of gas from the beer and carbonated water plus soap will produce stable foam (non-ideal solution). In the carbonated water the solution will fizzle (ideal solution). You can produce the same effect by shaking the glasses (physical effect).

There is a lot more to ruminal dCO2… if we can measure it, we can prevent many nutritional diseases in ruminants.

As the effervescence of CO2 is disrupted, dCO2 will increase leading to the nutritional and physiological changes that we observed during ruminal acidosis.