Using n-alkanes and other plant wax components to estimate intake, digestibility and diet composition of grazing/browsing sheep and goats

The use of plant-wax markers for estimating forage intake, diet composition and supplement intake in grazing/browsing sheep and goats is reviewed in relation to some of the shortcomings of pre-existing techniques. The saturated hydrocarbons (alkanes) of plant wax are well validated as markers for estimating intake. Alkane-based estimates of intake have the advantage of accommodating individual differences in digestibility and those arising from supplement/forage interactions. Alkanes can also provide an estimate of diet composition and hence the inputs required to estimate herbage intake. Total intake can thus be partitioned into intake of individual species. It is probable that the alkane approach to estimating diet composition can discriminate fewer species in the diet of sheep and especially goats, than these animals encounter in complex plant communities. We discuss approaches to coping with this issue, such as grouping species in diet composition estimates, and the use of other plant-wax markers as diet composition markers. The long-chain alcohols and fatty acids are shown to have particular promise for discriminating a greater number of species in the diet. We then discuss the estimation of supplement intake using plant hydrocarbons, as a special case of the estimation of diet composition. Finally, we demonstrate that when supplement intakes are known, alkane-based estimates of the supplement proportion in the diet can be used to estimate the intake of all dietary components, without the need to dose animals with synthetic alkanes.