Validation of the alkane technique to estimate diet selection of goats grazing heather–gorse vegetation communities

Abstract

The effect of n-alkane faecal recovery on the accuracy of diet composition estimates, when increasing the number of diet components, was studied. Seven dietary treatments, composed of different proportions of herbaceous (Lolium perenne and Trifolium repens) and woody species (Erica umbellata, Erica cinerea, Calluna vulgaris, Erica arborea and Ulex gallii) were offered to 28 goats housed in metabolism crates. Diet composition was estimated from alkane concentrations in diet and faeces, with and without correction for incomplete faecal recoveries, using least-squares procedures and was compared with the known diet proportions. There were no significant differences between measured proportions of dietary components and those estimated with alkanes when applying the faecal recovery corrections. In contrast, the proportions calculated without faecal recovery correction differed significantly (p < 0.05) from the actual proportions, overestimating feeds with higher content of long-chain n-alkanes. The diet composition affected significantly the faecal recovery of alkanes if there were significant differences on in vivo digestibility. The n-alkane faecal recoveries decreased as the diet digestibility increased. The results obtained show that the application of the alkane methodology for grazing animals should be preceded by calculation of the actual alkane faecal recoveries for each type of vegetation community and experimental conditions.

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

“…For cattle, a positive association between CCL and LCOH FR was found. A similar trend was observed for horses and cattle when using LCFA (Ferreira et al, 2010) and alkanes (Ferreira et al, 2007 and2009a), and also in other ruminant species when studying LCOH (Ali et al, 2004;Dove and Charmley, 2008), LCFA (Ali et al, 2004;Ferreira et al, 2009b and and alkanes (Dove and Mayes, 2005;Ferreira et al, 2005 and2009a;Charmley and Dove, 2007). These data indicated that markers behave differently in the gastro-intestinal tract of ruminant and nonruminant species, and suggest that the disappearance of those with the shorter carbon-chain in the gut of ruminants occurs to a greater extent than in non-ruminants.…”

“…As recognized in previous studies (Dove and Mayes, 2005;Ferreira et al, 2005 and2009a;Oliván et al, 2007b), the major limitation of the application of faecal markers in grazing studies is their dependence on the use of accurate FR values to obtain accurate estimates of diet composition. In this study, the most accurate estimates of diet composition for both species were obtained when using the mean faecal concentration for the total of animals within 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

“…As Elwert et al (2008) discussed, the assumption of equal recoveries for a given marker compound is a necessary condition of using alkanes (or LCOH) to estimate diet composition and thus intake by the labelled-supplement method. Ferreira et al (2005) reported a significant negative relationship between diet digestibility and faecal alkane recovery. By contrast, in the present study there was no relationship between diet digestibility and faecal LCOH recovery.…”

Diet selection and live-weight changes of two breeds of goats grazing on heathlands

“…Biomass of tall heather was assessed twice (June 2003 and2005) from 10 to 20 Erica shrubs randomly selected in each grazed plot and in an adjacent ungrazed control plot. One shoot per shrub was cut at ground level and green shoots and leaves were manually sorted from the woody stems.…”