The goal of the present study was to evaluate the dynamics of fecal excretion of the following digestion markers: indigestible dry matter (DMi), indigestible neutral detergent fiber (NDFi), and indigestible acid detergent fiber (ADFi) as internal markers and the external marker chromic oxide (Cr2O3). Five Holstein-zebu steers with 240 kg average weight were used in three 12-day experimental periods, being the first seven days for animal adaptation. Previously to the beginning of the experimental period, the animals were submitted to a 10-day period of adaptation to facilities and experimental management. They were fed ad libitum with sorghum silage and maintained in individual pens. The Cr2O3 was offered twice daily at 08:00 and 17:00 h, 5 g each, during the whole experimental period. Then, the daily marker fecal excretion pattern was characterized by means of the Gauss-Newton algorithm to fit a Fourier series model. A descriptive graphic evaluation of the fitted function showed that the total amplitude of cycles was lower for ADFi than the other markers, with values of 4.71%, 1.83%, 2.42% and 1.74% for Cr2O3, DMi, NDFi and ADFi, respectively, in relation to the estimated mean concentration of each. In turn, the fundamental period of the markers excretion patterns were significant showing cycle lengths of 3.25, 3.47, 3.46 and 3.74 hours for Cr2O3, DMi, NDFi and ADFi, respectively. As a conclusion, the mean fecal concentration of all markers might be obtained through two daily samplings at intervals from each other of 3, 9, 15 or 21 hours.
fecal excretion; indigestible acid detergent fiber; indigestible dry matter; indigestible neutral detergent fiber
