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Title: Effect of ensilage and digestion on the components of the cell wall of perennial ryegrass, white clover and lucerne
Author: Barwick, Jacqueline Mary
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1989
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Abstract:
The structure of the components of plant cell walls have been reviewed with respect to their utilisation as energy sources for ruminants. Various in vitro methods for assessing forage utilisation were compared, but emphasis was placed on the artificial rumen system Rusitec. The principles of silage production were reviewed and the known effects of ensilage on the plant cell wall components discussed. The first series of experiments investigated the detailed composition of the cell wall of a variety of perennial ryegrass harvested at four stages of growth. Each stage of growth was ensiled in nylon bags in a farm scale silo and changes in the composition of the cell walls were determined. The results showed an overall loss of total dry matter from all four stages of growth during ensilage. There were indications that the maturity of the grass could affect the losses of cellulose during fermentation, with greater loss being seen from the more mature cuts of grass. The only loss apparent from all the cuts of grass was of glucose derived from the hemicellulose. Losses of arabinose from the hemicellulose were seen in the third and fourth cuts of grass during ensilage and xylose was lost from the fourth cut during ensilage. Apparent loss of lignin on ensilage was seen in the third and fourth cut of ryegrass. As it was in these cuts that loss of cellulose and hemicellulose was seen, it seems likely that there was solubilization of a lignin-carbohydrate complex, which would be lost in the silage effluent. Since one aim of the programme was to compare members of the Gramineae family with members of the Leguminosae family, a second series of experiments was carried out with white clover. The clover experiments were carried out using both laboratory scale and farm scale silos. Laboratory scale silos using perennial ryegrass had been investigated prior to the start of this programme. Using laboratory scale silos it was found that additive-treated silages behaved differently to a water-treated (control) silage. Both a formic-acid additive and a formaldehyde additive seemed to increase the loss of cell wall carbohydrates during ensilage. Losses from the side chains of the hemicellulose were seen but no losses of lignin were found. The clover harvested for the farm scale silos was cut at three stages of growth, and it was possible to investigate changes in cell wall composition as the clover matured as well as when it was ensiled. A steady increase in the concentration of cellulose in the dry matter of the clover as it matured was seen, with a loss of cellulose during ensilage being seen from the second and third cuts of clover. Hemicellulose levels in the dry matter varied as the plant matured, probably due to changes in the leaf:stem ratio in the maturing plant. A loss of hemicellulose was seen from all cuts on ensilage, with greater loss being seen from the more mature cuts of clover. No loss of lignin was seen from any cut of clover on ensilage. A final ensilage experiment was carried out on lucerne. This experiment comprised of only one sample and the ensiled material was taken directly from a farm scale silo. During ensilage losses of cellulose and lignin were seen from the lucerne, but there was no loss of hemicellulose. Although Tilley and Terry type in vitro digestions were used, most emphasis was placed on the Artificial Rumen System (Rusitec) to investigate the rate of utilisation and digestion of ensiled forages. These experiments examined the total loss of dry matter as well as the loss of individual components from the ensiled cell wall. The pattern of fermentation of the ensiled forages was determined from the volatile fatty acid profiles and from the gas production, particularly methane. The water solubility of the silages showed that the clover silage had the highest ratio of cell contents to cell wall, and it was thought that this contributed to the difficulty of maintaining a stable Rusitec system when using clover silage. The grass silage cell walls were more digestible than those of the lucerne silage and clover silage. This was reflected in the higher digestibility of the cellulose and hemicellulose from the grass silage. Loss of lignin was seen from all three silages after seventy two hours digestion in the Rusitec system. It was suggested that this was not true digestion, that is no breakdown products would be available to the rumen micro-organisms for metabolism, but represented the formation of a lignin-carbohydrate complex. It was suggested that this could prevent the rapid lowering of pH necessary for the proper preservation of silage, and the maintenance of a low pH necessary for the formation of a stable silage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.796284  DOI: Not available
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