Fecal excretion patterns and short term bias of internal and external markers in a digestion assay with cattle

The objective of this work was to evaluate the fecal excretion profile and the short term bias of the external markers chromic oxide and titanium dioxide and the internal markers indigestible dry matter (iDM), indigestible neutral detergent fiber (iNDF) and indigestible acid detergent fiber (iADF) in a digestion trial with cattle fed different diets. Fourteen F1 Red Angus × Nellore bulls averaging 12 months old and 287 kg were kept in individual stalls. The animals were fed elephant grass silage, corn silage or signal grass hay, supplemented or not with 20% of concentrate mixture. The experiment consisted of two 13-day experimental periods according to a 2 × 2 Latin square design with seven squares grouping. The animals received 10 g of chromic oxide and 10 g of titanium dioxide through esophageal sounder daily. Fecal grab samples were obtained directly from the rectum of the animals at 1:30 a.m., 3:00 a.m., 4:30 a.m., 6:00 a.m., 7:30 a.m., 9:00 a.m., 10:30 a.m., 12:00 p.m., 1:30 p.m., 3:00 p.m., 4:30 p.m., 6:00 p.m., 7:30 p.m., 9:00 p.m., 10:30 p.m. and 12:00 a.m. There was no effect of forages or concentrate levels on the dimension of excretory cycle. The fundamental period of excretory cycle was 15.06 and 18.66 hours for chromic oxide and titanium dioxide, respectively and 9.93, 9.29 and 10.55 hours for iDM, iNDF and iADF, respectively. The oscillation range was higher for external markers. Considering the characteristics of all evaluated markers together, it is recommended fecal sampling designs with at least four collections, distributed during the day or only in the diurnal period for obtaining fecal excretion estimates free of short term bias