Farm Animal Metabolism and Nutrition

342 W.C. Ellis et al.

Fig. 16.3.

Distributions of residence times of indigestible fibre (IF), in rumen digesta as modelled by one or two sequential pool models.

Assuming instantaneous

mixing and equal probability for escape of IF yields an exponential distribution of residence times for IF; the age-independent

mixing pool. An exponential dilution

of the IF remaining in the age-independent mixing pool, FIFR, reflects an age-constant dilution rate,

k^2

. The non-exponential distribution of IF residence time in the

age-dependent mixing pool reflects an age-dependent rate of escape of IF from the single age-dependent mixing pool,

λe

, or the initial entry pool,

λ^1

of two

sequential pools models. Because of relatively slow mixing of rumen digesta, the age-dependent profile of FIFR portrayed here f

or rumen digesta cannot be resolved

from sampling rumen digesta but must be resolved by sampling IF in the rumen efflux. The mean ruminal residence time is the sam

e whether estimated by one age-

dependent pool model or by the two sequential pool model.