Effects of animal species and diet composition on long-chain alcohol faecal recoveries and accuracy of subsequent diet composition estimates

Long-chain alcohols (LCOH) were evaluated as markers to estimate diet composition of ruminant species fed with two distinct diets composed of herbage and “heather” (Ericaceae species). Diet composition was estimated using LCOH, combined or not with n-alkanes and/or long-chain fatty acids (LCFA), by least-squares procedures, using faecal concentrations corrected or not for their incomplete recovery. The effect of grouping plant species with similar marker profiles and the impact of feeding selectivity (FS) within the dietary group on the accuracy of diet composition estimates were also evaluated. Results showed the usefulness of LCOH as diet composition markers. The LCOH were incompletely recovered in the faeces of all animal species and tended to increase with carbon-chain length in a curvilinear manner in cattle and sheep, whereas in goats this association was better described by a linear function. Accuracy of estimates was higher when LCOH and n-alkane markers were combined. For all marker types, results indicated that a correction of marker faecal concentrations to incomplete faecal recovery is needed to obtain accurate diet composition estimates. Grouping plant species with similar marker profiles improved the accuracy of estimates, whereas combination of marker types minimized the FS effect within the dietary group.