European Journal of Scientific Research - EuroJournals

Nutritive Evaluation of Some Trees and Browse Species from Scotland 312
Introduction
Nutrition is perhaps the most important consideration in livestock management. The nutritive value of
a feed is essentially a function of the availability of its energy and nutrient contents. According to Van
Soest (1983), nutritive value is multifaceted, but useful attributes of a feed are feed consumption and
digestibility. Browse (shrubs and tree foliage) plays a significant role in providing fodder for ruminants
in many parts of the world (Adugna et.al. 1997). Tree fodder is generally richer in protein and minerals
and is used as a dry season supplement to poor quality natural pasture and or fibrous crop residues
(Devendra, 1990; Kibbon and Orskov, 1993).
In vitro methods for laboratory estimations and feed degradation are important tools for
ruminant nutritionists. The Hohenheim in vitro gas test is extensively used for the estimation of in vivo
digestibility and metabolizable energy for ruminants (Menke et al., 1979). Internationally, the gas test
is of increasing interest because of the possibility of estimating the extent and rate of degradation in
one sample by time series measurement of the accumulating gas volume (Blummel et al., 1990;
Khazaal et al., 1993, Orskov, 2000). However, the presence of tannins and other phenolic compounds
in a large number of nutritionally important shrubs and tree leave decrease their utilization as animal
feed. In general, most browse species contain phenolic compounds that reduce digestibility and
availability of protein, and contribute to unpalatability and reduced intake (Woodward and Reed, 1989;
Kumar and Vaaithiyanaathan, 1990; Kibon and Ørskov, 1993). There have been several studies aimed
at inactivating phenolic compounds using polyvinyl pyrolidone (PVP) or polyethylene glycol (PEG).
Thus PEG has been used to adsorb plant phenolics during the extraction of enzymes because of its
hydrophobic properties (Badran and Jones, 1965). A potential increase in in vitro (Kumar and
Vaithiyanathan, 1990) and in vivo (Jones and Mangan, 1977) digestibility of tannin rich feeds by the
addition of PEG-4000 has also been reported.
While the nutritional potential and limitations of many tropical and Mediterranean browse
species have been documented, comparatively little has been done on temperate trees species. Thus, the
objective of this study was to assess the nutritive value of some tree species from Scotland based on
their in vitro gas production, DM degradability in sacco and in vivo digestibility.
Materials and Methods
The forages used in the study were 1. Pinus sylvestris L. (Scots pine), 2. Lolium perenne L. (grass)
/Trifolium repens L. (Clover) mixture, 3. Calluna vulgaris L. (Heather), 4. Picea sitchensis (Bong.)
Carr. (Sitka spruce), 5. Chamaenerion angustifolium (L.) Scop. (Roseby willowherb), 6. Luzula
sylvatica (Great Woodrush), 7. Pseudotsuga menziesii F. Mirb. (Douglas fir), 8. Fagus sylvatica L.
(Beech), 9. Vaccinum myrtillus L. (Vaccinum), 10. Brassica oleracea (Cabbage), 11. Acer
pseudoplatanus L. (Sycamore), 12. Juncus effusus L. (Soft Rush)
Most of the tree leaves and browse species were hand harvested at Macaulay Research
Institute's experimental station at Glensaugh, Aberdeenshire, Scotland. The L. perenne was machine
harvested while the B. oleracea was purchased from a local farmer. The samples were oven dried at
70ºC for 48 hours and milled using a 1-mm screen.
In vitro gas production
In vitro gas production was measured using the method described by Blummel and Orskov (1993) by
incubating the forage samples with buffer and rumen fluid and recording the volume of gas produced
over time. Measurements were made after 3, 6, 12, 24, 48, 72 and 96 hours of incubation. Analysis was
carried out in triplicate in the presence and absence of 200mg PEG, molecular weight 4000 (Sigma-
Aldrich Company Ltd, Poole, Dorset, UK). The gas syringes were incubated by suspension from a rack
fitted above a water bath. The rumen fluid was taken from two sheep, fitted with permanent rumen
cannulae, receiving a diet of dried L. perenne pellets and hay.