Measurement of dietary nutrient intake in free-ranging mammalian herbivores

Abstract

The nutrient intakes of mammalian herbivores depend on the amount and the nutrient content of the plant species and plant parts which they eat. We review the merits of oesophageal-®stulated (OF) animals, microhistological procedures, stable C-isotope discrimination and plant cuticular-wax markers as methods for estimating diet composition and intake in both ruminant and non-ruminant herbivores. We also brie¯y discuss methods based on grazing behaviour measurements or on H 2 O or Na turnover, and methods for estimating supplement or soil intake. Estimates of intake in ruminants are often based on separate measurements of faecal output and herbage digestibility. We review this approach and emphasize that, under some circumstances, the applicability of in vitro digestibility estimates based on OF extrusa is questionable. We discuss how plant-wax marker patterns can be used to check whether OF and test animals are consuming similar diets, but also emphasize that a major advantage of the use of plant-wax markers is that this approach may obviate altogether the need for OF animals. Estimates of total herbage intake can be partitioned into the intakes coming from different plant species and=or parts, provided diet composition can be measured. Diet composition estimates based on C-isotope discrimination have the major disadvantage that they cannot be taken to species level. By contrast, microhistological methods can identify many plant species in extrusa, digesta or faeces, but often a large proportion of plant fragments remains unidenti®able. Plant-wax hydrocarbons show great promise as markers for estimating diet composition and intake. However, we suggest that to be applicable in complex plant communities there is a need with this method either to recruit a wider range of wax markers (e.g. alcohols, sterols, fatty acids) or to use it in combination with other methods. We suggest that, in turn, this generates an urgent need for research on statistical aspects of the combined use of markers or methods, in relation to the error structures of the data or methods being combined and the standard errors of the resultant estimates of diet composition and intake. We conclude by discussing the extension of intake and=or diet Abbreviation: OM, organic matter.

The importance of grasslands for animal production and other functions: a review on management and methodological progress in the tropics

“…There has been substantial development of plant wax components as markers to measure forage intake, diet composition and digestibility (Mayes and Dove, 2000;Dove, 2010). These plant wax constituents vary greatly among plant species or plant morphological components, and are largely excreted in faeces.…”

Evaluation of n-alkanes and their carbon isotope enrichments (δ13C) as diet composition markers

“…One of the requirements for estimating intake accurately using this approach is that the faecal recovery rates of the dosed and herbage n-alkanes should be similar Bezabih, Pellikaan, Tolera and Hendriks n-Alkanes and their carbon isotopic enrichments (Dove and Mayes, 1991). Generally, pairs of n-alkanes with consecutive carbon chain lengths are reported to have similar recovery rates (Mayes and Dove, 2000). As a result, a combination of either C 31 /C 32 or C 33 /C 32 has been used for this purpose.…”

“…Understanding the type of plant species selected by the animal and the contribution of each species to the total intake could give an insight into the nutritional status of the animal and offer a feasible range management strategy to optimise resource utilisation (Dumont et al, 2002). However, measurement of feed intake, diet composition and nutrient digestibility in free-ranging animals remains a challenge in nutritional studies -E-mail: derseh7@yahoo.com because of the inherent errors associated with the methods that are used at present (Dove and Mayes, 1991;Mayes and Dove, 2000).…”

Using n-alkanes to estimate diet composition of herbivores: a novel mathematical approach

“…For instance, the group of legumes is not adequate to estimate nitrogen intake since species within this group may have quite different nitrogen content (Mayes and Dove, 2000). Although Mayes and Dove (2000) suggest that n-alkanes can be used to differentiate plant parts in the diet of herbivores in our work 'dietary component' always refers to plant species (whole sample of plant leaf and stem). Indeed plant species accounts for more than 85% of the variation in n-alkane concentrations over plant parts .…”

“…N-alkanes have been used to estimate diet composition of domestic animals (Salt et al, 1992;Duncan et al, 1999;Hutchings et al, 2000) and, less frequently, of wild herbivores (Bugalho et al, 2001;Hulbert et al, 2001;Rao et al, 2003). N-alkanes are long-chain saturated hydrocarbons widespread in plant cuticles which can be recovered, after correcting for differential digestibility, in herbivore faeces as they are chemically inert Mayes and Dove, 2000). Additionally, since plant species are characterised by different concentrations of n-alkanes, the chemical markers recovered in faeces can be used to identify and quantify the plants ingested by herbivores.…”