The effect of wilting time and number of film wrap layers applied to baled grass on silage quality
By R. Fychan, D.R. Davies and R. Jones
R. Fychan and D.R. Davies are r esearch scientists, Nutrition and Microbiology Team, Plants, Animals and Microbial Sciences Department, at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, Wales
Raymond Jones, was Leader of Livestock Systems and Integrated Land Use, at IGER |
Four layers of silage film are commonly used to wrap silage bales in the UK. The study described below shows the results from a comprehensive study of both physical and chemical changes in baled silage when grass is film wrapped with different numbers of layers and at a range of dry matter contents.
Materials and Methods
A hybrid ryegrass sward was mown and wilted for 24, 48 or 72 hrs
Sub plots of these were wrapped with either four, six or eight layers of film with each treatment having three bales. All treatments were inoculated and all bales were weighed and sampled prior to wrapping with 750mm width film. Prior to opening, film seal was evaluated by evacuating each bale and measuring the time taken for the vacuum to drop from 250Kpa to 200 Kpa. Bales were opened, weighed and visual surface mould cover was assessed. Four 50mm cores of silage were sampled from each bale for chemical analysis and dry matter recovered was calculated from the difference between the dry matter at ensiling and the dry matter at opening.
Results
The dry matter content of the forage increased significantly with increased wilting time. No differences were observed in water soluble carbohydrates (WSC), nitrogen or ash contents of the forage with increased wilting, but a trend indicating a decrease in the digestibility (DOMD) of the forage with increase wilting time was observed (P = 0.083).
Film seal was less effective in bales wilted for only 24 hrs and may be due to the physical changes in shape and structure of the wetter bales. Increasing the number of film layers improved the film seal. Mould coverage on the bales was reduced by wilting for 72 hrs compared with 24 and 48 hrs. Applying 6 layers of film significantly reduced mould coverage on the bales compared to applying 4 layers, but applying 8 layers resulted in only a small reduction when compared with applying 6 layers. Dry matter recovery increased with increasing dry matter and with increasing film layering, suggesting improved fermentation.
Silage DM and pH increased in response to increased wilting time (P<0.001), whilst ammonia, lactate and acetate decreased in response to wilting time (P<0.001). Silage DM increased linearly in response to increased film layering (P<0.001). Lactate and acetate content reduced linearly in response to increase layering (P<0.05) possibly due to a more efficient and rapid fermentation.
Table 1 - Effect of film layering on film seal, mould cover and DM recovery
|
4 Layers |
6 Layers |
8 Layers |
| Film Wt (g) |
766 |
1111 |
1461 |
| Layers |
4.1 |
6.3 |
8.6 |
| Press drop (sec) |
47 |
76 |
111 |
| Mould cover (%) |
0.48 |
0.10 |
0.06 |
| DM recovery (%) |
89.6 |
91.8 |
92.5 |
Table 2 - Effect of film layering on silage quality and fermentation
| |
4 Layers |
6 Layers |
8 Layers |
| DM (g/Kg) |
368 |
382 |
384 |
| pH |
4.2 |
4.2 |
4.2 |
| Nitrogen (g/Kg DM) |
22 |
22 |
22 |
| Amm-N (g/Kg N) |
40 |
40 |
40 |
| Lactate (g/Kg DM) |
23.6 |
22.5 |
21.2 |
| Acetate (g/Kg DM) |
7.3 |
6.8 |
6.3 |
| WSC (g/Kg DM) |
132 |
140 |
150 |
Table 3 - Effect of wilting on film seal, mould cover and DM recovery
| |
24hr Wilt |
48hr Wilt |
72hr Wilt |
| Press drop (sec) |
53 |
94 |
87 |
| Mould Cover (%) |
0.23 |
0.27 |
0.14 |
| DM Recovery (%) |
87.0 |
92.9 |
94 |
Table 4 - Effect of wilting on silage quality and fermentation
| |
24hr Wilt |
48hr Wilt |
72hr Wilt |
| DM (g/Kg) |
282 |
380 |
472 |
| pH |
3.9 |
4.2 |
4.5 |
| Nitrogen (g/Kg DM) |
23 |
22 |
21 |
| Amm-N (g/Kg N) |
46 |
39 |
35 |
| Lactate (g/Kg DM) |
33.5 |
22.2 |
11.4 |
| Acetate (g/Kg DM) |
8.9 |
6.4 |
5.1 |
| WSC (g/Kg DM) |
101 |
153 |
169 |
Conclusions
Increasing the number of film layers applied to grass bales reduced air ingress, reduced silage DM loss and mould growth and resulted in a more efficient fermentation. So increasing bale film layers results in more silage of a better quality to feed to livestock.
Acknowledgments
This work was funded by bpi.agri Films and Dow Europe.
< back
