Ytterbium oxide has the same accuracy as chromic oxide for estimating variations of faecal dry matter output in dairy cows fed a total mixed ration at two feeding levels
Résumé
Daily herbage intake by ruminants at grazing can be estimated from faecal output and herbage digestibility. Chromic oxide has long been used as an external marker to estimate faecal dry matter (DM) output. The aim of this experiment was to determine the performance of ytterbium oxide compared to chromic oxide as an external marker for estimating variations of faecal DM output in dairy cows. Both markers were compared on eight Prim’Holstein lactating dairy cows, of which four were fistulated. Cows were offered a total mixed diet based on maize silage either at 100% or 70% of ad libitum DM intake, according to a single 2×2 reversal design with 2 experimental periods of 3 weeks. Faecal recovery of markers was determined over the last five days of each period by total faecal collection or by faecal sampling only during milking times. The between-day and the within-day variability of faecal marker concentrations were also investigated, as well as the between-day variability of faecal marker concentrations during the transition between periods 1 and 2. Both markers over-estimated the actual faecalDMoutput due to an incomplete faecal recovery. The average faecal recovery was slightly greater for Yb than for Cr (0.93 vs. 0.89). Faecal recovery of Yb and Cr was unaffected by feeding level irrespective of the faecal collection method. Ytterbium showed similar between-day and within-day variability of faecal concentration as Cr during the experiment (steady-state period), and similar between-day variability of faecal concentration as Cr during the transition period (non steady-state period). We conclude that ytterbium oxide used as a digestive marker seems to have the same accuracy as chromic oxide for estimating daily faecal DM output variations in dairy cows fed a total mixed ration, at low and high feeding level.