In order to understand better some of the reasons for differences
between forage plant species in
digestibility, different parts of nine plant species in either milled
or chopped (1 cm lengths) form were
examined for in vitro digestibility and in milled form for
neutral detergent fibre and lignin. The nine
species were: Trifolium repens L., Medicago sativa L.,
Desmodium intortum (Mill.) Urb., Brassica
napus L., Lolium perenne L., Festuca arundinacea
Chloris gayana Kunth, Cenchrus ciliaris L.
and Zea mays L. In each case early harvesting was compared with
later harvesting in each of two
years. The plants were grown in spring–summer in a heated glasshouse.
The forage at the early harvest was, on average, 1–4% units
more digestible in vitro than that at
the later harvest and generally slightly lower in lignin and neutral detergent
fibre content. However, the stems of Z. mays were higher in neutral
detergent fibre at the early than at the later harvest.
The leaf sheaths of L. perenne and F. arundinacea
were more digestible than the leaf blades. L.
perenne was more digestible than F. arundinacea in both
sheaths and blades. The sheaths and blades
of C. gayana and C. ciliaris were less digestible
and had a higher neutral detergent fibre content than
those of L. perenne and F. arundinacea. The leaf
blades, excluding the midribs, and the stems and leaf
sheaths of Z. mays were all rather high in digestibility
when milled and moderately low in neutral
detergent fibre and lignin; the leaf blade midribs of Z. mays
were less digestible and higher in neutral
detergent fibre than the stems and similar to the stems in lignin
content. The leaflets of T. repens had
an appreciably lower neutral detergent fibre content than the
stolons and petioles and a rather lower
lignin content in dry matter and yet were, if anything, less
digestible than the stolons and petioles.
The stolons of T. repens were much more digestible than the stems
of M. sativa and D. intortum. The
digestibility of D. intortum was low in all the plant parts
examined, leaflets, petioles and stems. In both
D. intortum and B. napus, the leaflets or leaf blades
much lower than the stems in neutral
detergent fibre and lignin and yet they were no more digestible than the
stems when milled.
The digestibility of chopped leaflets and leaf blades was similar
to that of milled leaflets and leaf
blades, but chopping rather than milling reduced the digestibility of
stems (particularly of those of
Z. mays), petioles, the leaf blade midribs of
Z. mays, and, to some extent, leaf sheaths.