Effect of length of ensiling on silo degradation and digestibility of structural carbohydrates of lucerne and orchardgrass
Introduction
Information on degradation of cellulose, hemicelluose, and pectin in silage during fermentation is scarce relative to that available for protein and non-structural carbohydrates (Michael, 1984). Similarly, little is known of the utilization of these components as microbial substrates during ensiling. While previous reports indicate that the bulk of the acids produced during ensiling originate from fermentation of water-soluble carbohydrates (WSC) (McDonald and Whittenbury, 1977), more recent reports suggest that substances such as protein and structural carbohydrates can also be substrates (McDonald et al., 1991). Cellulose, hemicellulose and pectin may also be substrates for microorganisms during fermentation, and their degradation during ensiling depends on interrelated factors, such as differences in forage species, forage growth stage at harvest, moisture content at ensiling and period and length of ensiling of forage, which are not fully understood.
When forage is ensiled, 2–3 weeks are generally required for it to attain stability (McDonald et al., 1991). The length of time that silage is stable due to a low pH depends on the nature of the fermentation in the ensiled crop.
This study examined the extent of degradation of structural carbohydrates of lucerne and orchardgrass after 5, 21 and 56 days of ensiling, as well as effects of silage structural carbohydrate degradation on in vivo digestibility in sheep.
Section snippets
Silage preparation
Lucerne (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) were harvested during the early flowering and heading stage, respectively, at the Obihiro University Farm, Japan. The two species were wilted for 8 h and chopped into lengths of 3–5 cm using a mechanical forage cutter. The two species were mixed individually and representative samples obtained. About 70 kg fresh matter of lucerne and 60 kg fresh matter of orchardgrass from the remaining content of each species were ensiled in
Composition of the fresh material and silages
The WSC contents of all silages declined (P<0.05) as the length of ensiling increased (Table 1). The hemicellulose and pectin contents decreased during ensiling in both species (P<0.05), while cellulose contents in both forages increased (P<0.05).
The pH values in both forages were lower (P<0.05) at 21 and 56 days of fermentation compared to 5 days, while the lactic acid concentration was higher (Table 2). The acetic acid content decreased (P<0.05) in lucerne, but increased in ochardgrass, as
Conclusion
The DM digestibility of lucerne and orchardgrass were not influenced by ensiling, however, losses of hemicellulose and pectin increased as ensiling advanced. Hemicellulose digestibility decreased in the lucerne and orchardgrass as ensiling advanced probably due to losses of these components during fermentation. Cellulose digestibility was higher in days 21 and 56 silages as a result of extra-cellular cellulase activity from silage microflora.
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