Alex,

I wouldn't be concerned with C exchange between methane and CO2. But I will
be weary of the different sources of CO2 in breath (i.e., rumen
fermentation and the host). If you are interested in the animal I would
measure blood CO2, if you interest is in the rumen, I would take samples
directly from the dorsal sac.

Regards

Juan


At 03:09 PM 4/8/2005, you wrote:

>Hi everyone,
>
>As anyone ever heard of a possible contamination of 13CO2 values in cows
>and steers breath samples due to isotopic exchange between CO2 and methane
>? If this is occuring, how fast could it affect carbon values ?
>
>Thank you !
>
>Alex
>
>Alexandre Myre, Research Officer, University Laval.