Oxygen-barrier film cover reduces silage losses

Oxygen-barrier film cover reduces silage losses

Incomplete or inadequate silo covering results in increased silage losses during the storage period.

By J.M. WILKINSON*

*J.M. Wilkinson is with the University of Nottingham's Sutton Bonington Campus in Loughborough, U.K.

THE successful preservation of crops as silage relies on the establishment and maintenance of anaerobic conditions within the silo or bale.

Material in the peripheral areas of the silo or bale is prone to deterioration during the storage period due to permeation of oxygen through standard polyethylene (PE) films (Borreani and Tabacco, 2012a and 2012b) and also due to damage to the film caused by wind, birds or animals.

A layer of blackened and slimy spoiled silage may be seen at the outermost layer of the silo, with areas containing visible mold development.

This review is about losses due to spoilage of the outer layers of silos and bales, the aerobic stability of silage and the role of the oxygen-barrier (OB) silo and bale covering system in reducing losses, improving silage aerobic stability and enhancing the nutritional value of silage.

 

Losses from outer layer

A 1,000-metric ton bunker silo that's 12 m wide x 30 m long x 3.5 m tall contains about 25% of the original ensiled crop in the top 1 m, and 50% of the volume of a 1.2 m-diameter round bale is within 12.5 cm of the outer surface.

Covering silos and wrapping bales with standard PE film reduces losses by protecting the crop from rain but does not prevent oxygen permeation into the silo. Spoilage is usually seen under the top covering film sheet or bale wrap film and at the sides and shoulders, where effective compaction can be difficult to achieve and silage density is lowest.

Loss of organic matter (OM) from bunker silos is highest in the uppermost 50 cm layer. Studies with farm-scale silos in the U.S. over a four-year period revealed that the loss of OM from the top 50 cm during the storage period averaged 47% of the original crop ensiled in uncovered silos, compared to 20% in covered silos (Table 1).

Visually, the top surface "shrinks" during the storage period, and a black, foul-smelling, slimy layer with a mud-like texture comprises the uppermost layer. The extent of the shrinkage depends on the effectiveness of the covering system and can add up to as much as a 36 cm decrease in height in uncovered silos (Whitlock et al., 2000).

 

Effects on animals

Spoiled silage judged subjectively by visual inspection to be unfit for use as animal feed (i.e., inedible) is normally discarded as waste material. However, surface-spoiled silage can occasionally be given to livestock.

The accidental inclusion of spoiled silage in the ration constitutes a risk to animal health and can reduce livestock productivity. The probability of including spoiled silage in the diet is greatest when silage is unloaded mechanically in the dark.

There is little research evidence on the effects spoiled silage has on the animal. In an experiment with cattle fitted with ruminal cannulae, silage intake and digestibility were reduced significantly when spoiled corn silage from the top meter of an unsealed silo was mixed — at 25% of total silage dry matter (DM) in the ration (5% of which was the slime layer in the uppermost 50 cm) — with unspoiled silage from the same original crop but stored in a sealed "AgBag" silo (Table 2).

Inclusion of spoiled silage in the ration appeared to destroy the integrity of the forage "mat" in the rumen (Whitlock et al., 2000). The pH of the spoiled silage was higher (4.8 versus 3.9) and DM was lower (264 g versus 380 g DM/kg) than for the normal silage.

 

Silage aerobic stability

Some silage is very unstable when exposed to air at feedout and can deteriorate in less than 24 hours of exposure to the atmosphere (Danner et al., 2003). In a survey of corn silages, Kristensen et al. (2010) found that aerobic stability was very poor, averaging only 37 hours in un-inoculated material.

The low stability reflected relatively high counts of yeasts and molds in the crop at the time of harvest — 6.36 and 5.64 log10 colony-forming units (CFU) per gram of fresh weight, respectively. Inoculation of crops with homofermentative lactic acid bacteria can result in reduced aerobic stability that's associated with low concentrations of acetic acid (Weinberg et al., 1993; Danner et al., 2003; Hocknell and Yeates, 2005).

Wilkinson and Davies (2013) and Wilkinson and Chamberlain (2016) highlighted the significance of the aerobic deterioration of silage in terms of hazards to animal health through, for example, the production of mycotoxins and bacterial endotoxins in spoiled silage.

The penetration of air into the exposed silo feedout face of normally consolidated silage in bunker silos is a depth of 1-2 m (Honig, 1991; Weinberg and Ashbell, 1994; Honig et al., 1999). If samples of silage taken 20-50 cm behind the exposed bunker silo feedout face or beneath the outer layer of a bale show temperatures higher than ambient, then the material has most likely been exposed to air for more than two days, and DM loss will be about 5% compared to unexposed silage (Wilkinson and Davies, 2013). Loss of DM in silage exposed to air for more than seven days is likely to be at least 10% of unexposed silage (Wilkinson et al., 1998).

Many silos are too wide to achieve the proposed target feedout progression rate of 1 m of exposed face per week (15-30 cm per day) in winter and 2 m per day in summer (Wilkinson, 2005).

Feedout progression rates in bunker silos on 54 commercial farms in Italy were in a range of 7-25 cm per day in winter and 8-33 cm per dayin summer (Borreani and Tabacco, 2010). In this survey, temperatures of up to 54 degrees C were recorded in the peripheral areas of silos, and almost all samples taken horizontally to 20 cm behind the exposed silo face in peripheral areas had temperatures that were more than 5 degrees C higher than samples taken to the same depth from the core mass of the silo.

Exposure of silage to air during the feedout period has detrimental effects not only on silage composition but also on animal intake. There was a 27% reduction in DM intake of corn silage exposed to air for four days prior to being offered to goats (P < 0.05) and a 66% reduction after eight days of exposure to air compared to no exposure (P < 0.05; Table 3). In this trial, the silage was stable in air for two days. DM, pH and counts of yeasts, molds and aerobic mesophilic bacteria increased during exposure to air, while concentrations of fermentation products decreased. The accumulated increase in silage temperature above ambient was the best predictor of intake.

 

Oxygen-barrier system

OB film (e.g., Silostop from B. Rimini Ltd.) reduces silage surface spoilage by restricting oxygen permeation and the growth of molds and butyric acid bacterial spores in the peripheral areas of the silo or bale (Borreani and Tabacco, 2008).

The results of a meta-analysis of 51 comparisons (41 with bunker and clamp silos, and 10 with baled silage) between standard PE film and OB film are shown in Table 4. The mean loss of DM or OM in the upper layer of bunker and clamp silos was reduced from 19.5% of the original crop ensiled for standard film to 11.4% for OB film. Inedible silage was reduced in five comparisons from 10.7% of the total crop ensiled for standard film to 2.96% of the total crop ensiled for OB film.

In 10 comparisons with baled silage, losses were reduced from 7.68% of total DM ensiled for standard film wrap to 4.56% for OB film wrap. Borreani and Tabacco (2012a) found that counts of yeasts and mold were 10-fold less in bales wrapped with OB film than in bales wrapped with the same number of layers of standard film. With baled red clover silage, the percentage of bale surface covered by mold was 18.1% for four layers of standard film wrap and 5.1% for four layers of OB film wrap. At six layers of film wrap, molds covered 6.0% of the bale surface for standard film and 0.7% of the bale surface for OB film wrap.

In 11 trials with corn silage, the average aerobic stability — defined as the time it takes for the temperature of exposed silage to rise 2 degrees C above ambient — of silage from the upper layer of the silo was 75 hours for material stored under standard PE film and 135 hours for silage stored under OB film (Table 4).

The increase in mean aerobic stability of 60 hours is of practical value, especially when the speed of removal of silage from the exposed silo face is relatively slow, as well as in warmer seasons and in tropical climates when ambient temperature and relative humidity are elevated. Improved aerobic stability is probably a reflection of slower development of yeasts and molds (Orosz et al., 2012) and Acetobacter pasteurianus (Dolci et al., 2011) due to restricted oxygen ingress into the outer layer of the silo prior to full exposure of silage to air at feedout.

The hygienic quality of the silage may also be enhanced in silage stored under the OB film system, with potential benefits to animal and human health, since aflatoxins have been found to develop in corn silage exposed to air during feedout (Cavallarin et al., 2011).

Effects on the animal of using OB film to cover silos and wrap bales have yet to be fully elucidated. Two trials have been reported in which dairy cows were given balanced total mixed rations containing 53% of the total diet DM as corn silage stored under either standard or OB film (Table 5). Silage judged subjectively to be "inedible" was removed and was not given to the animals, so only "good" silage within the outer layers of the silo was used for the experiments.

There were no differences in silage composition between covering treatments, and differences in animal performance were relatively small, most likely reflecting the removal of inedible silage from the silos prior to feeding. Silage digestibility in trial 1 was numerically higher for the silage covered by the OB film plus standard film than for silage covered by the standard film alone.

Feed conversion efficiency was numerically higher for OB film than for standard film in both trials, and milk net energy conversion efficiency was significantly higher (P = 0.02) for OB film than for standard film in trial 2, probably reflecting the higher digestibility of silage covered by the OB film than by standard film.

 

Conclusions

Incomplete or inadequate silo covering results in increased silage losses during the storage period. Spoiled silage reduces feed intake and digestibility. Slow progression rates during the feedout period can result in losses through aerobic deterioration, with serious detrimental effects on the nutritional value of the silage.

OB silo covering film reduces losses, increases silage aerobic stability and can improve the efficiency of silage use.

 

References

Amaral, R.C., J.L.P. Daniel, A. Sa Neto, A.W. Bispo, J.R. Lima, E.H. Garcia, M. Zopolatto, M.C. Santos, T.F. Bernades and L.G. Nussio. 2012. Performance of Holstein cows fed diets containing maize silage from silos with different covering methods. In: K. Kuoppala, M. Rinne and A. Vanhatalo (eds.). Proceedings of the XVI International Silage Conference, Finland. p. 470-471.

Bispo, A.W., D. Junges, C. Kleinshmitt, L. Custodio, J.R. Lima, J. Fernandes, J.L.P. Daniel and L.G. Nussio. 2013. Performance of dairy cows fed diets containing corn silage from silos with different sealing strategies. III International Symposium on Forage Conservation & Quality, Campinas, Brazil. July.

Bolsen, K.K. 1997. Issues of top spoilage losses in horizontal silos. In: Silage: Field to Feedbunk. Northeast Regional Agricultural Engineering Service Publication NRAES-99. p. 137-150.

Borreani, G., and E. Tabacco. 2008. Low permeability to oxygen of a new barrier film prevents butyric acid bacteria spore formation in farm corn silage. J. Dairy Sci. 91:4272-4281.

Borreani, G., and E. Tabacco. 2010. The relationship of silage temperature with the microbial status of the face of corn silage bunkers. J. Dairy Sci. 93:2620-2629.

Boreani, G., and E. Tabacco. 2012a. Using a special EVOH grade in stretch film manufacturing reduced dry matter losses and spoilage and increases hygienic quality of baled silages. In: K. Kuoppala, M. Rinne and A. Vanhatalo (eds.). Proceedings of the XVI International Silage Conference, Finland. p. 300-301.

Borreani, G., and E. Tabacco. 2012b. Special EVOH films with lowered oxygen permeability reduce dry matter losses and increase aerobic stability of farm maize silages. In: K. Kuoppala, M. Rinne and A. Vanhatalo (eds.). Proceedings of the XVI International Silage Conference, Finland. p. 302-303.

Cavallarin, L., E. Tabacco, S. Antoniazzi and G. Borreani. 2011. Aflatoxin accumulation in whole crop maize silage as a result of aerobic exposure. J. Sci. Food & Ag. 91:2419-2425.

Danner, H., M. Holzer, E. Mayrhuber and R. Braun. 2003. Acetic acid increases stability of silage under aerobic conditions. Appl. Env. Microbiol. 69:562-567.

Dolci, P., E. Tabacco, L. Cocolin and G. Borreani. 2011. Microbial dynamics during aerobic exposure of corn silage stored under oxygen barrier or polyethylene films. Appl. Env. Microbiol. 77:7499-7507.

Gerlach, K., F. Ross, K. Weiss, W. Buscher and K.-H. Sudekum. 2013. Changes in maize silage fermentation products during aerobic deterioration and effects on dry matter intake by goats. Ag. Food Sci. 22:168-181.

Hocknell, P., and M. Yeates. 2005. Latest tests on silage additives. Kingshay Farming Trust. March. p. 10-12.

Honig, H. 1991. Reducing losses during storage and unloading of silage. In: G. Pahlow and H. Honig. (eds.). Forage Conservation Towards 2000. Landbauforschung Volkenrode, Sonderheft 123, Braunchweig, Germany. p. 116-136.

Kristensen, N.B., K.H. Sloth, N.H. Spliid, C. Jensen and R. Thagersen. 2010. Effects of microbial inoculants on corn silage fermentation, microbial contents, aerobic stability and milk production under field conditions. J. Dairy Sci. 93:3764-3774.

Orosz, S., J.M. Wilkinson, S. Wigley, Z. Biro and J. Gallo. 2013. Oxygen barrier film improves fermentation, microbial status and aerobic stability of maize silage in the upper 30 cm of the silo. Ag. Food Sci. 22:182-188.

Weinberg, Z.G., and G. Ashbell. 1994. Changes in gas composition in corn silages in bunker silos during storage and feeding. Canadian Agricultural Engineering 36:155-158.

Weinberg, Z.G., G. Ashbell, Y. Hen and A. Azreli. 1993. The effect of applying lactic acid bacteria at ensiling on the aerobic stability of silages. J. Appl. Bacteriology 75:512-518.

Whitlock, L.A., M.K. Siefers, R.S. Pope, B.E. Brent and K.K. Bolsen. 2000. Effect of surface spoiled silage on the nutritive value of corn silage-based rations. Kansas State University Agricultural Experimental Station Report of Progress 861. p. 36-38.

Wilkinson, J.M. 2005. Silage. Chalcombe Publications, Lincoln, U.K.

Wilkinson, J.M., and A.T. Chamberlain. 2016. Silage and livestock health. Livestock. (In press).

Wilkinson, J.M., and D.R. Davies. 2013. The aerobic stability of silage: Key findings and recent developments. Grass & Forage Science 68:1-19.

Wilkinson, J.M., and J.S. Fenlon. 2014. A meta-analysis comparing standard polyethylene and oxygen barrier film in terms of losses during storage and aerobic stability of silage. Grass & Forage Science 69:385-392.

Wilkinson, J.M., G. Newman and D.M. Allen. 1998 Maize. Producing & Feeding Maize Silage. Chalcombe Publications, Lincoln, U.K. p. 40.

 

1. Effect of covering ensiled corn and forage sorghum with standard polyethylene film and car tires on loss of organic matter in upper layers of 127 commercial farm silos in Kansas (Bolsen, 1997)

 

-Loss of OM (%)-

Depth of sampling

Uncovered

Covered

0-50 cm

47.0

20.3

50-100 cm

11.3

4.5

 

2. Effect of including spoiled silage in the diet of beef cattle (Whitlock et al., 2000)

 

-Diet-

 

 

100% normal

75% normal/

 

 

silage

25% spoiled silage

P <

Dry matter intake (kg/day)

7.94

7.35

0.05

OM digestibility (%)

75.6

70.6

0.05

Digestible OM intake (kg/day)

6.00

5.18

0.05

 

3. Composition, accumulated temperature and goats' intake of corn silage after 0, 4 or 8 days of exposure to air (Gerlach et al., 2013)

 

--Days of exposure to air--

 

0

4

8

DM (% of fresh weight)

36.0

37.1

39.5

pH

3.9

4.2

5.8

Lactic acid (% of DM)

5.8

4.9

0.8

Acetic acid (% of DM)

1.3

0.9

0.3

Ethanol (% of DM)

0.6

0.4

0.01

Yeasts (log10 CFU/g)

4.6

7.2

7.3

Molds (log10 CFU/g)

2.4

2.8

4.2

Aerobic mesophilic bacteria (log10 CFU/g)

4.7

5.7

6.7

Accumulated temp. (degrees C above ambient)

-0.6

8.4

28.7

Intake (3-hour period, g)

646

626

280

 

4. Losses, inedible silage and aerobic stability of silage in top surface layer stored under standard PE film or OB film (Wilkinson and Fenlon, 2014)

 

 

-Std. film-

-OB film-

 

Parameter

n

Mean

Range

Mean

Range

P

Bunker and clamp silos*

 

 

 

 

 

 

Loss of DM or OM (% of crop ensiled)

41

19.5

-12.0 to +70.0

11.4

-8.9 to +38.0

<0.001

Inedible DM (% of total DM ensiled)

5

10.7

5.9 to 20.1

2.96

0.1 to 3.9

0.022

Aerobic stability (hours)

11

75.3

0** to 184

134.5

48 to 355

0.001

Baled silage

 

 

 

 

 

 

Loss of DM (% of total DM ensiled)

10

7.68

4.3 to 12.3

4.56

2.3 to 7.5

<0.001

*Includes drive-over piles and laboratory silos.

**Material already deteriorated at start of assessment.

 

5. Intake and milk production by dairy cows given diets based on corn silage stored under standard or OB films

 

-Trial 1*-

-Trial 2**-

 

Std. film

OB film (45 microns) +

Std. film

OB film

 

(200 microns)

std. film (200 microns)

(200 microns)

(125 microns)

Total DM intake (kg/day)

22.7

21.7

24.3

23.4

Milk yield (kg/day)

32.9

32.3

27.6

28.1

OM digestibility (%)

67.8

72.9

ND

ND

Milk protein %

3.34

3.29

3.48

3.53

Milk protein yield (kg/day)

1.10

1.06

0.94

0.96

Milk/kg DM intake

1.44

1.49

1.14

1.20

Milk net energy (Mcal)/kg DM intake

ND

ND

0.77

0.82***

*Amaral et al. (2012).

**Bispo et al. (2013).

***P = 0.02.

ND = not determined.

 

Volume:88 Issue:12

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