To examine the effects of diet manipulation on the litter
equilibrium NH3 gas concentration, a 19-L container was
pressed into the litter between the two feeders and the
drinker. The litter was prepared by first removing the top
5 to 10 mm, which typically consisted of a hard, dry,
crusted layer, and exposing wet litter. The removal of the
top layer was to ensure a more uniform estimate of
equilibrium NH3 gas concentration. The gas sampling
container contained a small fan to mix the sample air at a
constant velocity (1 m/s) to ensure that the surface-air
boundary layer was sufficiently disturbed. Every 2 min
for a period of approximately 20 min, the sampling line
was purged and a 2-mL sample of air was diverted from
within the container to a Bruel and Kjaerâ 1302 photoacoustic
infrared gas monitor6 to measure NH3 concentration.
The sampled air was then returned to the isolation
container. Equilibrium NH3 gas concentration was determined
as the steady-state concentration. Gas sampling
was repeated every week in each pen and required 1 full d.
Further details can be found in Ferguson et al. (1998)