The possible use of n-alkanes, long-chain fatty alcohols and long-chain fatty acids as markers in studies of the botanical composition of the diet of free-ranging herbivores

Abstract

SU MMARYFew methods exist for estimating quantitatively the diet composition of free-ranging herbivores. The current study examined whether long-chain fatty alcohols (alcohols) or long-chain fatty acids (acids) could be used along with n-alkanes to allow reliable diet composition estimates to be made in herbivores consuming complex diets. Twelve Scottish Blackface wether sheep housed in metabolism crates were fed four different mixtures of three plant species (three animals per mixture) for a sevenperiod experiment. Concentrations of cuticular wax n-alkanes, alcohols and acids were estimated in samples of individual plant species, and the faeces from animals that consumed mixtures of these species. These concentrations were then used to calculate the dietary proportions of each species by a least-squares optimization procedure. To explore the differences between the estimation methods (individual markers and their combinations), the mean squares of errors (EMS) between the actual and predicted proportions of plant species were calculated.In three out of the four mixtures, alcohols had the lowest discrepancies (lowest EMS values), followed by n-alkanes and then acids. Acids yielded the lowest discrepancy in one mixture and the highest in the others.It is concluded that, for this particular set of mixtures, alcohols had great potential to estimate composition of complex diets. However, the estimation using acids was less good and n-alkanes were of intermediate potential. Estimation from the combination of the three marker classes was always better than using the poorest individual marker. * Source: Clapham et al. (1987); Keir (2000). # Harvested material also contained some (<5 %) white clover (Trifolium repens), which is a perennial legume. The relatively high C 30 alcohol in ryegrass may reflect white clover contamination.

Application of long-chain alcohols as faecal markers to estimate diet composition of horses and cattle fed with herbaceous and woody species

“…In comparison with LCFA, LCOH showed lower total concentrations as observed by Ferreira et al (2015) with similar plant species. A similar trend was observed by Ali et al (2005) when comparing the concentration of these epicuticular wax compounds on 25 rangeland species of Sudan. By contrast, Lin et al (2009 and found a predominance of LCOH over LCFA in several Chinese grass species and other forages such as Chenopodium album, Medicago sativa and Bromus inermis.…”

“…In these situations, Ferreira et al (2009a) suggested that the combination of several faecal markers (alkanes, LCFA and LCOH) can provide a more specific fingerprint to each plant species, increasing the discriminatory power between them. To the authors' knowledge, there are no published studies using LCOH as markers for horses, previous studies with small ruminants (Ali et al, 2005;Lin et al, 2009 andFerreira et al, 2012 and2015) also observed greater accuracy when LCOH were used, compared with alkanes and LCFA. By contrast, Dove and Charmley (2008) obtained better estimates of diet composition of sheep when using alkanes compared with LCOH, due to high correlation between the LCOH profiles of two of the forage components (Phalaris aquatica and ryegrass).…”

“…Thus, their application may result in less accurate estimations of both diet selection and feed intake (Ferreira et al, 2007). To overcome these limitations, other epicuticular wax components such as long-chain fatty acids (LCFA) (Ali et al, 2005;Ferreira et al, 2009b;Lin et al, 2009), and long-chain fatty alcohols (LCOH) (Ali et al, 2004;Ferreira et al, 2012 and2015) have been suggested as additional markers to estimate diet composition of small ruminants. In fact, their utilization may increase the accuracy of estimates by providing additional discriminatory information to that supplied by alkanes.…”

The importance of grasslands for animal production and other functions: a review on management and methodological progress in the tropics

“…However, in some tropical grasses the concentrations of important alkanes may decrease markedly with increasing age of leaves (Laredo et al, 1991); this is of concern as the method depends on estimation of alkane concentration in the leaf ingested. A further difficulty is that some tropical forages and edible browses contain very low concentrations of alkanes (Laredo et al, 1991;Ali et al, 2005) so that the presence of these plant species in the diet could not be measured from faecal alkane concentrations. Even if these constraints associated with the markers can be overcome, a further consideration is that tropical native pasture grassland systems often contain a very large and diverse range of edible plant species.…”

Using the alkanes and long-chain alcohols of plant cuticular wax to estimate diet composition and the intakes of mixed forages in sheep consuming a known amount of alkane-labelled supplement

“…This resulted in reduced accuracy of intake estimation in diets containing large proportions of phalaris. In that study, we suggested (Charmley and Dove, 2007) that the accuracy of estimation of diet composition, and thus forage intake, could be increased by also using other cuticular wax markers such as the long-chain alcohols (LCOH), in the estimation of diet composition (Bugalho et al, 2004;Ali et al, 2005;Dove and Mayes, 2005).…”