The effect of in-silo addition of cellulases and hemicellulases on the chemical composition and nutritional value of silage

Brolly, Reginald Gareth (1986) The effect of in-silo addition of cellulases and hemicellulases on the chemical composition and nutritional value of silage. MSc(R) thesis, University of Glasgow.

Abstract

1. Aspects of digestion, control of food intake, plant cell wall structure and silage conservation are reviewed in relation to the breakdown of fibre constituents by the addition of polysaccharide-degrading enzymes. 2. A series of experiments with laboratory-scale silos was set up to examine the ability of the two cellulase/hemicellulase mixtures (ES 1 and ES 2; supplied by an industrial company) to degrade intact forage cell walls under conditions pertaining in the silo. Comparisons were made with activity-related additions of cellulase and hemicellulase preparations available commercially (Sigma Chemical Company). Three experiments examined the dose responses of the enzymes and the time course of their action. All silages were well preserved and there was no evidence of any adverse effects of enzyme addition on silage fermentation. Preparation ES 1 showed the greatest capacity to degrade cell walls as judged by reductions in neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations; at 500 mlt -1 NDF and ADF concentrations in grass silage were reduced by 122 and 79 g kgDM -1 respectively compared with the formic acid alone treatment. As the levels of enzyme addition were increased (up to a maximum of 2000 mlt -1) it became increasingly difficult to account for the products of NDF and ADF breakdown in terms of water soluble carbohydrate (WSC) or fermentation products. The shortest period over which enzyme action was studied was 14 days and by this time there were measurable reductions in the concentrations of NDF and ADF. 3. Eight 1-tonne silos were made, four from perennial ryegrass (Lolium perenne) and four from lucerne (Medicago sativa). The grass silages were treated with formic acid (3 t-1 ) and increasing additions of ES 1 and ES 2 (100, 300 and 500 mlt-1) used in a 50:50 combination. With the lucerne silages only the control had been treated with formic acid and the others with 125 mlt-1 ES 1, 250 mlt-1 ES 1/ES 2 and 10 mlt-1 ES 3 respectively, ES 3 being a third enzyme preparation supplied by the industrial company. All the silages were well preserved. The silages were used for studies on the disappearance of constituents from Dacron bags incubated in the rumen and in intake/digestibility trials with sheep. 4. Samples of the grass and lucerne silages were incubated in Dacron bags in the rumen in two cows fitted with rumen cannulas. The rate of loss of dry matter and fibre consituents were determined after 2, 7, 16, 24 and 48 h incubations. For the grass silages the rates of disappearance of DM and NDF were significantly greater (P<0.01) for the formic acid control treatment than for the enzyme treatments. For the lucerne silages the control treatment of formic acid alone had the lowest rates of disappearance of DM, NDF and ADF. Treatment with 125 mlt-1 ES 1 gave the greatest losses in DM, NDF and ADF at all incubation times (P<0.01). 5. The intake and digestibility of the silages was determined in vivo in sheep in two 4x4 Latin Square experiments; each period lasted 21 days with a faecal collection over the final 7 days of each period. The silages were offered ad-libitum and intakes were measured throughout the experiments. The digestibilities of the enzyme-treated grass silages were similar to those of the formic acid control and the DM and OM intakes of the enzyme-treated silages were significantly lower (P<0.01) than those of the silage treated with formic acid only; the intake was lowest for the highest addition of enzyme (500 mlt-1 ES 1/ES 2). A much greater effect of enzyme treatment was observed with the lucerne silages. There were reductions in the concentrations of NDF and ADF with all three enzyme treatments and there were increases in the digestibility of DM, OM and ADF for the silages treated with ES 1/ES 2 (150 mlt -1) and ES 3 (10 mlt -1) but not for the ES 1 treatment (125 mlt-1). The intakes of DM and OM were highest for the lucerne treated with ES 1/ES 2 and lowest for ES 1 treatment; the intakes of digestible OM were 19% higher for the ES 1/ES 2 treatment than for the formic acid control. 6. A final experiment investigated the feeding value of silage made in farm-scale bunker silos (50 t) filled with late cut ryegrass ensiled without additive , with formic acid (2.6 It -1) or with the addition of ES 1/ES 2 (400 mlt -1). Prior to the start of the experiment the digestibility of the silages was determined in sheep. The D0MD value of the silage was not increased by the enzyme additive. The feeding value of the silages was estimated using 12 lactating cows in an experiment of a cyclical design with 2 blocks of 6 animals and four 4-week periods per block. There were six dietary treatments consisting of each of the silages offered ad-libitum with concentrate supplements given at flat rates of either 6 kgd -1 or 9 kgd . Milk yield and food intake were recorded daily. The silages were well preserved and there was a reduction in the concentration of NDF and ADF with the enzyme-treated silage. At the 6 kgd -1 level of concentrates the intakes of all three silages were similar. However, at the 9 kgd -1 level the intake of the enzyme-treated silage was higher than that of the other two silages; the values (kgDM d -1) were; 8.49, 8.74 and 9.29 for the untreated, formic acid treated and enzyme-treated silage respectively. There were no differences (P>0.05) between silages in milk yield and composition. 7. It is concluded that the addition of the cellulase/hemicellulase mixtures at ensilage has clear potential for the improvement of the nutritional value of the resulting silage. Whilst there was no clear-cut evidence of an increase in DOMD in response to enzyme addition in these studies, improvements in the voluntary intake of silage were measured in two experiments. Further work is required to examine factors such as dose-rate of enzyme in relation to crop characteristics in terms of species, stage of maturity and pre-ensiling treatments such as wilting. The need for further investigation of the mode of action of the enzymes and a more detailed examination of the end-products of fibre breakdown is also evident.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Animal sciences
• Date of Award: 1986
• Depositing User: Enlighten Team
• Unique ID: glathesis:1986-76632
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 14:00
• Last Modified: 19 Nov 2019 14:00
• URI: https://theses.gla.ac.uk/id/eprint/76632