SU MMARYPrevious investigations have shown that the long-chain fatty alcohols and long-chain fatty acids of plant waxes have potential as diet composition markers. This study was conducted to measure faecal recoveries of long-chain fatty alcohols (C 20 -C 30 ) and long-chain fatty acids (C 20 -C 32 ) in sheep fed mixed diets. Methodology for quantitative analysis of these compounds in feed and faeces is also presented. The method was an extension of the original n-alkane method of Mayes et al. (1986) in which separate hydrocarbon (n-alkanes, n-alkenes and branched-chain alkanes), alcohol (free+ esterified) and acid (free+esterified) fractions could be obtained from a single sample. A fraction containing alcohols and sterols was eluted from the silica gel column after removal of the hydrocarbons. Sterols were removed from alcohols using aminopropyl solid-phase extraction columns. Alcohols were converted to their trimethylsilyl (TMS) ethers and run on a gas chromatograph (GC). Acids were extracted from the aqueous phase of saponification products after removal of hydrocarbons, alcohols and sterols, purified through silica gel columns and were converted into their methyl esters (FAMES) prior to analysis on a GC. Tests were carried out to evaluate the reproducibility of the results obtained from the analytical method developed for quantifying alcohols and acids. Twelve sheep, in metabolism crates, were offered (0 . 8 kg DM/animal/day) four different mixtures of hill grass (Agrostis capillaris), birch (Betula pendula) leaves and current season's growth of heather (Calluna vulgaris) and bilberry (Vaccinium myrtillus) for 17 days. Total daily faeces and feed refusals collections were carried out over the last 7 days. Faeces collections were bulked for each animal. Representative samples of feed, refusals and faeces were analysed for alcohols and acids using the described method. Faecal recoveries of alcohols and acids were calculated from the ratio of output and input of each marker. The results showed high, though incomplete, faecal recoveries for both alcohols and acids. Alcohols had consistently higher faecal recoveries compared with acids. Mean (¡S.E.) faecal recovery values for alcohols C 20 , C 22 , C 24 , C 26 , C 28 and C 30 were 0 . 58¡0 . 04, 0 . 67¡0 . 01, 0 . 72¡0 . 008, 0 . 80¡ 0 . 007, 0 . 94¡0 . 005 and 1 . 01¡0 . 02, respectively, whereas those of acids C 20 , C 22 , C 24 , C 26 , C 28 , C 30 and C 32 were 0 . 47¡0 . 02, 0 . 57¡0 . 02, 0 . 61¡0 . 02, 0 . 77¡0 . 017, 0 . 84¡0 . 01, 0 . 79¡0 . 015 and 0 . 84¡0 . 013, respectively. Increasing chain-length had a significant effect (P<0 . 05) on the recoveries of both alcohols and acids (R 2 =0 . 808, 0 . 741, respectively). Different dietary plant mixtures had no effect (P>0 . 05) on the recoveries of alcohols and acids in faeces.

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.

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