The use of the alkane technique to estimate diet selection of sheep grazing grass–clover/heather–gorse vegetation communities

Abstract

AbstractThe n‐alkane technique was evaluated for estimating the diet composition of sheep grazing in heathlands. Six dietary treatments, composed by different proportions of herbaceous (Lolium perenne and Trifolium repens) and woody species (Erica umbellata, Erica cinerea, Calluna vulgaris and Ulex gallii) were offered to 24 sheep housed in metabolism crates. Diet composition was estimated from alkane concentrations in diet and faeces, by least‐squares procedures, using all available alkanes (C1) from C25 to C33, or only those with higher concentration (C2): C27, C29, C30, C31 and C33. Additionally, the effect of applying mean treatment faecal recoveries (R1), mean faecal recoveries of all experimental diets (R2) or no faecal recovery correction (R3) was studied in both selections of alkanes (C1 and C2). No significant differences were observed between the use of all alkane information (C1) or limited number of alkanes (C2) in the diet composition calculations. There were no significant differences between measured proportions of dietary components and those estimated with procedures R1 and R2. In contrast, the proportions calculated with R3 procedure differed significantly (P < 0.05) from the measured proportions, overestimating feeds with higher content of long chain n‐alkanes. The results indicate that correction of faecal alkane concentrations to allow for incomplete faecal recovery is necessary in order to obtain accurate estimates of diet composition, using mean treatment faecal recoveries (R1) or mean faecal recoveries of all experimental diets (R2). Copyright © 2006 Society of Chemical Industry