Comparison of models estimating digesta kinetics and fecal output in cattle from fecal concentrations of single-dosed markers of particles and solutes

Fecal concentrations of chromium and number of sequential compartments with constant cobalt, following a single labeling dose of Cr-mor- increase of t he outflow rate from each compartment to danted fiber and Co-EDTA to the ru men, were the next one, without allowance for any bypass fluxes. obtained f rom two experiments: one with beef cows fed All the models could fit all th e data sets. Goodness of two diets before and after parturition, and one wi th fit was the best with M2 and the worst with M3. growing bull calves fed two diets of high and low fill Goodness of fit of the particle curve with M 2 was volume. These data were used to compare three comparable to that of M 4. Model M1 estimated the optional models that estimated the whole digestiv e tract kinetics of particles and solutes and fecal output, shortest and M3 estimated the longest total retention with a fourth model that estimated p article kinetics time (TRT) for particles (72.8, 85.0, and 91.2 h for only. The first model (M1) assumes separate routes MI, M2, and P113, respectivel y), and the partition of for particles and solutes: with two bypass fluxes (i.e., retention time between the different pools differed simultaneous flu xes from one pool to more than one among models. There were no significant differences other pool) in the particle route and one in the solute among m odels in their estimates of solute TRT (30.2, route. The second model(M2) i s similar to M1, but 31.5, and 30.8 h for MI, M2, and M3, respectively). al lowance is made for some of the particles to pass to Fecal output estimatio ns were similar among models, the solute route. The third model (M3) assume s that all of them overestimating the predetermined measurements of the kin etic variables in the solute route are by 9.5 to 113%. The r(2) of the line ar regression identical to the correspondent variables in the particle of t he estimated on the determined fecal output was route. The fourth model (M4 ) assumes an unspecified .74,.75: and .70 for M1, M2, and M3, respectively.