Use of chromium mordanted neutral detergent residue as a predictor of fecal output to estimate intake in grazing high producing Holstein cows

Two experiments were conducted to evaluate use of chromium mordanted neutra l detergent residue (Cr-NDr) and cobalt EDTA (Co-EDTA) as predictors of dry matter intake (DMI) in high producing grazing dairy cows. The first experi ment was conducted with 10 lactating Holstein cows individually fed a total mixed ration (TMR) in confinement, and dosed with Cr-NDr and Co-EDTA twice daily at milking times for 12-days to validate the markers used for the se cond experiment. The Cr-NDr accounted for 96% of the variation (r(2)) in DM I, while Co-EDTA underpredicted DMI by 43% (r(2) = 0.65). The second experi ment was conducted on a pasture-based dairy farm, to evaluate the use of Cr -NDr to predict DMI of grazing dairy cows. 15 and 14 high producing dairy c ows in trial 1 and 2, respectively, were dosed twice a day at milking times with Cr-NDr for 12-days. Mean total DMI estimated from marker recoveries w ere unrealistically high (5.95 and 5.52% of body weight for trials 1 and 2, respectively). It was concluded that either diurnal variation in fecal exc retion of the marker or a failure in the technique of collecting pasture sa mples that reflected the cows' true grazing selection in order to determine pasture composition occurred. (C) 2001 Elsevier Science B.V. All rights re served.