| By Dr eng. Barbara Wróbel, Dr eng. Halina Jankowska-Huflejt |
In 2007, Dow commissioned a study to the Institute for Land Reclamation and Grassland Farming (IMUZ) in Falenty, Poland, to compare the effects of the number of wrap layers (2, 4, 6, and 8 layers) on silage quality, dry matter losses, mould coverage and nutritive value of silage.
Methodology
The trial was conducted under farm conditions in the Experimental Farm of IMUZ in Falenty. Silages were made from a first cut of permanent meadow sward mown in May 2007. The herbage was wilted for 24 hours, raked and baled. The dry matter (DM) level in meadow sward at ensilage was 460.5 g/kg.
Forty experimental big bales (about 400 kg/bale) were produced. The bales were wrapped after transport to their place of storage using 2, 4, 6 and 8 layers of plastic film. Bales were wrapped with 500 mm wide stretch film.
After 3 weeks storage period each bale was tested to evaluate the effectiveness of film seal by creating a vacuum within the bale and measuring the time taken for the pressure to drop.
During November (after 190 days of ensilage) bales were opened. Immediately after unwrapping each bale was assessed for mould coverage. The representative sample of silage was taken for chemical analyses from each bale. DM losses of silage were estimated by the differences between dry matter weight of ensilaged forage and dry matter weight of obtained silage.
Results
Applying a different number of wrap layers affected the film seal. In bales wrapped with two layers the film seal was less effective, while increasing the number of layers significantly improved the film seal: the time taken for air to re-enter the four and six layers bales was five to seven times longer compared to the two layers bales.
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The effectiveness of film seal had an effect on visible moulds coverage. Bales wrapped with two layers of film recorded 45% of moulds coverage on the bale surface. Increasing the number of wrap layers reduced the risk of air penetrating the bale and significantly decreased mould coverage. As a result, the mean mould cover was only 9.5% and 1.5% on bales wrapped respectively with six and eight layers.
An additional result of interest is the significant reduction of DM losses as the numbers of layers increased from two to eight. Applying four layers of films resulted in 3-times lower DM losses then when wrapped with only two-layers and 10-times lower DM losses when wrapped with six layers. Bales wrapped with eight layers, DM losses were very small and in many bales were nil.
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Generally the number of layers had no significant influence on the silage chemical composition. Only the butyric acid, total protein and WSC (Water Soluble Carbohydrates) concentration significantly increased as the numbers of layers increased from two to eight.
No significant differences were observed as to lactic acid fermentation levels in bales with higher number of wrap layers. The ammonium, lactic acid and acetic acid concentration decreased with the increase in the number of layers. Also a trend indicating an increase in NEL (Netto Energy Lactation) energy concentration in silage was noticed with the increase of the number of wrap layers.
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Conclusions
The study proves that wrapping silage bales in four to six layers of film provides a more robust oxygen barrier resulting in reduced loss of dry matter in silage from yeasts and moulds, as well as significant improvements in the quality and nutritive value and a more stable and consistent silage at feed out. The data confirms that applying two layers of silage wrap film does not guarantee an effective film seal on bales, while 6 layers of film has been shown to give the greatest return.
Table 1 - Effects of film wrap layers on silage DM losses, quality and nutritive value
| Examined Parameters |
Number of Wrap Layers |
| 2 |
4 |
6 |
8 |
| Film Seal: |
|
|
|
|
| Drop from 250 to 150 kPa (s) |
21.2 |
104.2 |
148.0 |
207.1 |
| Drop from 350 to 250 kPa (s) |
8.2 |
56.2 |
90.8 |
134.9 |
| Visible moulds coverage and DM losses: |
|
|
|
|
| Mould cover (% bale surface) |
50.0 |
21.2 |
9.5 |
1.5 |
| DM losses (%) |
2.52 |
0.88 |
0.25 |
0.07 |
| Dry matter content and chemical composition: |
|
|
|
|
| Dry matter (g kg-1) |
389 |
410 |
411 |
424 |
| pH |
4.87 |
4.95 |
4.81 |
5.09 |
| NH3-N (g kg-1 total N) |
62.3 |
51.3 |
53.6 |
40.3 |
| Lactic acid (g kg-1 DM) |
41.7 |
38.1 |
42.3 |
29.9 |
| Acetic acid (g kg-1 DM) |
19.6 |
11.0 |
16.4 |
15.0 |
| Butyric acid (g kg-1 DM) |
0.11 |
0.23 |
0.22 |
0.86 |
| Stability (days) |
6.0 |
7.4 |
8.6 |
8.0 |
| Nutritive value: |
|
|
|
|
| Total protein (g kg-1 DM) |
123.8 |
130.7 |
130.6 |
118.0 |
| WSC (g kg-1 DM) |
136.1 |
139.1 |
129.1 |
159.5 |
| Ash (g kg-1 DM) |
73.3 |
68.5 |
78.1 |
67.7 |
| NEL (MJ kg-1 DM) |
5.55 |
5.60 |
5.63 |
5.82 |
Source: IMUZ Research
| Dr. Barbara Wróbel and Dr. Halina Jankowska-Huflejt are researchers at the Institute for Land Reclamation and Grassland Farming at Falenty, Poland |
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