The use of even-chain alkanes sprayed onto herbage as rate of passage markers in goats

An experiment was conducted with Saanen goats fed fresh grass ad libitum to compare ⁵¹Cr-mordanted fibre and even-chain alkanes sprayed onto either grass leaves or stems to estimate faecal output, total mean retention time (TMRT) and parameters obtained from faecal marker concentration curves, such as k₁ (slow rate of passage), k₂ (fast rate of passage) and transit time (TT). ⁵¹Cr-mordanted grass showed the lowest fractional rates of passage (k₁ and k₂) and hence the largest value of TMRT. There were not significant (P > 0.05) differences between even-chain alkanes sprayed onto leaves or stems for k₂, TT and TMRT, but k₁ estimates were higher (P < 0.05) for stems than for sprayed leaves. Despite the marker used, TMRT values were negatively correlated with the level of dry matter intake (r = ? 0.81, ? 0.80 and ? 0.80 for ⁵¹Cr-mordanted fibre and even-chain alkanes adsorbed onto leaves or stems, respectively). Average faecal outputs estimated from faecal concentrations of ⁵¹Cr-mordanted fibre and even-chain alkanes were not different from the actual outputs but there were differences between markers in the accuracy of estimation. The highest mean square prediction error (MSPE) and the poorest correlation between observed and estimated faecal output values corresponded to even-chain alkanes adsorbed onto stems. Values estimated using ⁵¹Cr-mordanted fibre and even-chain alkanes adsorbed onto leaves were significantly correlated with faecal outputs (r = 0.94 and r = 0.92, respectively), with MSPE being greater for the latter marker.