Contribution of storage and structural polysaccharides to the fermentationprocess and nutritive value of lucerne ensiled alone or mixed with cereal grains
G. Jaurena et G. Pichard, Contribution of storage and structural polysaccharides to the fermentationprocess and nutritive value of lucerne ensiled alone or mixed with cereal grains, ANIM FEED S, 92(3-4), 2001, pp. 159-173
The low content of water soluble carbohydrates (WSC) and the high buffering
capacity usually constrains lucerne (Medicago sativa) ensilability. Howeve
r, there are other sources of readily fermentable substrate and positive ef
fects of adding cereal grains to wet silages have been reported. An experim
ent was carried out to study the contribution of hemicellulose, cellulose a
nd natural or added starch to the silage fermentation process, and in vitro
digestibility and gas production. A crop of lucerne (10% blooming) was cho
pped, inoculated with lactic acid bacteria, and ensiled in microsilos with
four treatments: alone (T0), or with 50 kg/t of sucrose (SU), barley (BRL),
or maize (MZ). Microsilos were incubated for 47 days. Polysaccharide recov
ery was determined by the mass balance technique, and starch by dacron bag.
Except for SU, all treatments were apparently limited by the amount of WSC
needed to sustain good silage fermentation. As expected, SU produced an ex
cellent fermentation but despite initial WSC differences, there were no sig
nificant differences with BRL for total fatty acids, lactic and acetic acid
, total acidity, pH and NH3-N. Fermentation characteristics of MZ were gene
rally worse than BRL's and similar to T0's ones. Hemicellulose was extensiv
ely hydrolysed (T0: 59.5%; MZ: 38.1%; BRL: 48.8%; and SU: 46.8%). Cellulose
was almost quantitatively recovered and starch recovery averaged 70% for T
0 and BRL, and approximately 100% for MZ and SU. The type of cereal added a
ffected starch recovery using the dacron ba technique (MZ: 77%; BRL: 47%; P
< 0.05). True dry matter digestibility was the same for all treatments (fr
esh lucerne: 81.3%; T0: 80.7%; MZ: 81.8%; BRL: 80.5%; and SU: 82.1%), and n
eutral detergent fibre digestibility (NDF-D) of silages was reduced in rela
tion to the fresh material (fresh lucerne: 55.1%; T0: 48.8%; MZ: 51.9%; BRL
: 45.3%; and SU: 46.7%). Although all silages showed a rapid in vitro ferme
ntation pattern, gas production (48 h) of SU and BRL (265.4 and 260.5 ml/g
DM) was greater than T0 and MZ (246.0 and 244.6 ml/g DM) (P < 0.05). It can
be concluded that starch hydrolysis depends on the type of grain, and that
starch from barley and legume cell wall components could supply additional
fermentable substrate to the ensiling process. These data also showed that
ensiling reduced NDF-D and suggest that labile NDF fractions removed durin
g the ensiling process were later accessible during the in vitro fermentati
on. (C) 2001 Elsevier Science B.V. All rights reserved.