PSXIV-18 - Fecal Dry-matter Output Determination from Irregular Marker Doses

Abstract: Automated head chamber systems (AHCS) configured to offer known quantities of feed to individual animals may potentially be used to dose animals with an indigestible marker. Fecal marker analysis commonly assumes steady-state fecal concentration represented by average measured concentration. Due to irregular voluntary use of an AHCS, it’s not likely steady-state fecal concentrations would be achieved. Our objective was to determine whether steady-state assumptions could be relaxed and fit measured concentrations to multi-dose digesta kinetics models to produce reliable fecal output estimates when dose times and amounts are known but irregular. We used individually penned, rumen fistulated Dexter steers (n = 4, initial BW = 322 ±15 kg) limit fed a diet of hay and protein supplement in two experiments. First, after a 7-d acclimation period, steers were given a dose of TiO₂ through the rumen fistula. On d 14, the steers received another dose. Over a period of 120 h after each dose, 14 fecal samples were collected. In Exp. 2, 7-d after the steers had received their 2^nd dose, steers received the first of 6 daily doses, then on d 7 no dose, and on days 8 to 12 daily doses resumed. Beginning on d 7, when dose was skipped, fecal sampling began and over a 120-hr period, 14 fecal samples were collected. During both experiments total fecal collections were also made. For Exp. 1, marker concentration data were fit to a G2 digesta kinetics models and for Exp. 2, concentration data were fit to a multi-dose G2 digesta kinetics model. The multi-dose approach models over time, the sum of each known pulse, assuming identical digesta kinetics for each dose. Measured fecal output in Exp. 2 averaged 2,525 g/d, but the estimates obtained from fitting measured concentrations to multi-dose digesta kinetics models was significantly less (P = 0.005, 2,265 g/d).