Herbage intakes by individual animals can be estimated accurately using dosed alkanes and those of plant
cuticular wax (Mayes et al. 1986; Dove and Mayes 1996). Individual supplement intakes have been
estimated accurately using markers such as chromic oxide (eg Dove and Coombe 1990), tritiated water (eg
Dove et al. 1995) or tritiated gypsum (Dove and Coombe 1990). However, all of these methods require
chemical analyses in addition to those needed to estimate herbage intake by the alkane method and, in the case
of the tritiated markers, have the disadvantage of being radioactive.
Supplement intake could be measured by estimating total intake using the alkane method, and then estimating
the proportion of supplement in that total, based on the pattern of alkane concentrations in supplement,
herbage and faeces (Dove and Moore 1995; Dove and Mayes 1996). Unfortunately, many supplements (eg
legume grains and solvent-extracted oilseed meals) contain little or no alkanes. We therefore evaluated a
synthetic alkane (octatriacontane; C38 alkane) and a non-plant alkane mixture (beeswax), as markers for
estimating supplement intake in housed sheep. In the first case, supplement intakes were calculated using the
C38 alkane as an external marker added to the supplement. In the second, the proportions of perennial
ryegrass chaff and supplement in the diet were estimated using the pattern of alkane concentrations in chaff,
supplement and faeces (Dove and Moore 1995). Synthetic C28 alkane was also mixed with the beeswax
prior to use, to ensure that the alkane pattern in the beeswax-based mix did differ markedly from that of the
chaff.