Evaluation of <i>n</i>-alkanes, long-chain alcohols, and carbon stable isotope enrichments of <i>n</i>-alkanes as diet composition markers in free-grazing animals

Context Plant species exhibit different patterns of plant cuticular wax profiles, which can potentially be used as diet composition markers in free-grazing herbivores. Aims Evaluate the suitability of the plant cuticular n -alkanes, long-chain alcohol (LCOH) profiles and carbon stable isotope enrichment (&#x3b4;13 C) of n -alkanes as markers in the estimation of diet composition of grazing animals. Methods Forage samples were collected from 100 representative quadrats of 0.5m&#xd7;0.5m at 10m transects and sorted by species and pooled from different quadrats to obtain enough quantities of representative individual species. In total, 10 dominant forage species were identified and analysed for n -alkanes and LCOH by gas chromatography, and the isotopic ratio by using gas chromatography&#x2013;combustion&#x2013;isotope ratio mass spectrometry. Principal component analysis (PCA) was used to identify inter-species differences in the concentration patterns of plant wax components. Key results Odd-chain n -alkanes comprised the highest proportion of the total n -alkane concentration, ranging from 79% in Ischaemum afrum to 95% in Haplocarpha hastata . n -Alkanes C31 , C29 and C33 were the most abundant with an average of 167, 80 and 61mg/kg DM, in that order, in all species. Even-chain LCOH comprised the highest proportion of the total LCOH concentration, accounting for 92% in Brachiaria scalaris to 97% in Ischaemum afrum . The dominant even-chain LCOH were C30 OH, C32 OH, C28 OH and C26 OH, with an average concentration of 362, 348, 266 and 237mg/kg DM respectively, across species. The &#x3b4;13 C of n -alkanes showed large variations among forage species, ranging from &#x2212;19.7&#x2030; in Andropogon amethystinus to &#x2212;40.6&#x2030; in Trifolium mattirolianum . The result of the PCA showed that 81% of the variance in the pattern of concentrations of n -alkanes was explained by the first two principal components compared with 69.3% and 82.9% in the case of LCOH and &#x3b4;13 C of n -alkanes, respectively. Conclusions Noticeable variations were observed for forage species studied in the patterns of plant wax components. Implications The differences in the patterns of concentrations of n -alkanes, LCOH and &#x3b4;13 C of n -alkanes could be suitable as markers for diet composition estimation of grazing animals.