The objective of this study was to determine the biases in estimating fecal excretion from the internal markers indigestible dry matter (DMi), indigestible neutral detergent fiber (NDFi) and indigestible acid detergent fiber (ADFi) and the external marker chromic oxide (Cr2O3) in a digestion trial with ruminants. Five crossbred Holstein-Zebu castrated males with 240 kg average weight were used. The research consisted of three twelve-day experimental periods, from which the first six days were assigned to animal adaptation. The animals were fed sorghum silage ad libitum in individual pens. Six sampling schedules were adopted: 16 daily collections, at 1.5 hourly intervals; eight collections made during daylight starting at 7 a.m. at 1.5 hourly intervals; eight collections made at night starting at 7 p.m. at 1.5 hourley intervals; four collections made in the day every three hours; four collections at night every three hours and two collections, at 7 a.m. and 4 p.m. The chromic oxide was the indicator with the smallest bias in the long term, but underestimated fecal production. The internal markers overestimated this variable and the NDFi presented the smallest bias. For the short term biases, all the indicators over estimated fecal production: the smallest short term bias was registered for MSi. The NDFi was the indicator that presented the smallest total bias, even though it underestimated fecal production.
indigestible acid detergent fiber; chromic oxide; indigestible dry matter; estimation biases; indigestible neutral detergent fiber
