RESUMEN
We executed two studies to investigate time to reach steady state (EXP1) and diurnal variations (EXP 2) of markers, in order to recommend spot fecal sampling in sheep. Eight lambs were used in EXP 1. Each animal has received titanium dioxide (TDOX) and chromium oxide (COX) together during two periods of 15 days. Thirty sheep of the Santa Ines breed were used in EXP 2. Fecal samples were taken with 2-h intervals in the last 5 days of each period, simultaneously to total feces collection. A sine-cosine model was used to evaluate EXP 2, and broken-line model for EXP 1. TDOX could complete its recovery after 2.3 days, and it could accurately promote fecal estimates after 3 days of marker infusion. COX could stabilize after 4.1 days, and it could promote fecal estimates after 5 days. However, estimated fecal excretion became similar to total feces output after 3 days for TDOX and after 6 days for COX. For both markers, a total 6 days of adaptation period could be summed to a 3-day collection period. Spot sampling was similar to total fecal output at 6:00 to 8:00 on morning and between 5:00 and 7:00 on afternoon for TDOX. Also, COX could be sampled at 6:00 to 8:00 on morning and between 5:00 and 7:00 on afternoon. External markers could be evaluated from 3-day fecal spot collection. Fecal collections could be made before the morning feeding, and around 6 p.m. for both markers.