Evaluation of external markers to estimate fecal excretion, intake, and digestibility in dairy cows.

The objective of this study was to compare the use of an external marker titanium dioxide (TiO₂) as an alternative to chromic oxide (Cr₂O₃) in dairy cows. Four dairy cows were allocated in individual pens and fed concentrate supplement and Pennisetum purpureum cv. Cameroon cut daily. Fecal excretion, forage and total dry matter (DM) intakes, and digestibility were measured and estimated with TiO₂ and Cr₂O₃. Chromic oxide overestimated and TiO₂ tended to overestimate fecal excretion compared with total fecal collection. Forage and total DM intakes were overestimated by Cr₂O₃. The apparent DM digestibility was underestimated by Cr₂O₃ and TiO₂. The organic matter (OM) digestibility was underestimated by both markers. There were greater mean bias, mean squared prediction error, and root of the mean squared prediction errors for all parameters estimated with Cr₂O₃. In conclusion, estimates using TiO₂ were more precise and accurate indicating that it can replace Cr₂O₃ as an external marker for grazing dairy cows.