MEKELLE UNIVERSITY

FACULTY OF DRYLAND AGRICULTURE AND NATURAL

RESOURCES

DEPARTMENT OF ANIMAL, RANGE AND WILED SCIENCE

Assignment on:

Biochemistry of Silage Production

For the course: Advanced Animal Nutrition (LPGS 514)

By: Tekleab Srekebrhan

(M. Sc. Student in Livestock production and pastoral development)

Submitted to: O.A Abu (Ph. D)

August 2006

Table of content

1. Introduction......................................................................................................................1

1.1 Advantages of silage-making...............................................................................................1

1.2 Disadvantages of silage making?.........................................................................................1

2. Discussion.......................................................................................................................2

3. The Fermentation Process..............................................................................................3

3.1 based on the type of microbe involved......................................................................3

3.2 Based on availability of oxygen the Silo....................................................................7

3.3 Other factors /Considerations.......................................................................................73.3.1 Plant Maturity and moisture Content.......................................................................................73.3.2 Nature of the plant......................................................................................................................83.3.3 Silage additives..........................................................................................................................8

4. Conclusion....................................................................................................................10

5. References.....................................................................................................................11

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1. Introduction

Silage is moist feed made by the transformation of plant materials to a preserved

fodder which will be achieved by maintaining the anaerobic condition in a silo

(Marshal, 1997, wikipedia). It is a biochemical process of both the plant and microbial

activities and their effect on the plant material.

Ensiling has been used in Sweden since the eighteenth century but it is during the last

50 years it has been fully developed (McDonald et al., 1991).

1.1 Advantages of silage-making

Silage making has some distinct advantages compared to grazing or hay-making. For

example, silage making allows:

Less risk with weather conditions. dry matter losses due to rainfall is minimized;

reduced loss of leaves and other high quality small plant parts in the field (compared

to hay-making);

it can stored or preserved for long period of time with minimum lose of nutrient

1.2 Disadvantages of silage making?

Silage making also has some limitations or drawbacks including:

requires high capital investment

once a silo is opened; silage should be removed on a daily basis

no off farm market opportunity

The main Objective of this term paper the biochemical change or reactions resulting

from the activities of plant enzyme and microbes during silage production process will

be reviewed.

The methods of organization is by - referring books Literatures, internet, personal

experience and unpublished materials

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2. Discussion

The biochemistry of Silage production involves any activities or reactions which takes

place and results alteration in the chemical and physical status of the ensiled material

The two main components in the biochemical process of silage production which

affect its nutritional value includes are:

1. The plant species and stages of harvest

2. The chemical change or reactions resulting from the activities of plant enzyme

and microbes during the harvesting and Storage period (which is the intended

matter to be discussed in this term paper).

Plant enzymes

These acts on plant tissue just after cutting and during the earlier stage in silo

undergoes respiration in which hexose sugars undergo glycolysis and subsequently

oxidation via TCA cycle to carbon dioxide, water and heat. This heat retain in the

herbage mass causing increase in temperature, which result in depletion of substrate

that subsequent fermentation may be adversely affect until the oxygen is removed

from the silo. (Mc Donald et al, 1995)

In addition to this the plant enzymes undergo proteolysis. Tremblay et al, 1981

indicates during silage fermentation, proteolysis reduces the nutritional value of

Nitrogen and decline as the pH falls.

Microorganisms

On the fresh herbage Aerobic fungi and bacteria are the dominant microorganisms.

But as anaerobic condition develop in the silo they are replaced by anaerobic bacteria

(Mc Donald et al, 1995)

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3. The Fermentation Process

Silage fermentation is a biological process whereby bacteria are responsible to

convert water-soluble carbohydrates to organic acids including lactic acid, acetic acid,

ethanol, and carbon dioxide. (http://www.asab.org.uk/asa /adjudications/).

Factors necessary for good fermentation are: anaerobic conditions (no air), proper

moisture, sufficient plant water-soluble carbohydrates/sugars, proper bacteria

(www.vigortone.com/silageinoculants.htm)

The fermentation processes of silage are classified based on the microbes involved in

the process or based on the absence or presence of oxygen in the chemical process.

3.1 based on the type of microbe involved

The desirable processes that take place in a silo with the microbe involvement may be

described by a sequence of four phases as follow:

Phase 1: Respiration (Fig 1)

Once a plant is cut and cells lose their structures, they continue to consume oxygen.

This

equation indicates respiration converts sugar into carbon dioxide, water, and heat.

Thus respiration results in loss of plant nutrients in the presence of oxygen with in 1 to

2 days (Michel Wattiaux). Oxygen also reduced and NADH2 is oxidized.

Fig 1 respiration process (plant enzymeSource http://www.forages.psu.edu/topics/hay_silage/preservation/silage_preserv/index.html

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Phase 2: Early fermentation

As oxygen is removed and fermentation begins, the bacteria become predominantly

facultative aerobic bacteria mainly enterobacteria, which converts water-soluble carbo-

hydrate into acetate, ethanol, hydrogen and CO2. As fermentation proceeds, entero-

bacteria become less competitive with decreasing pH, (Michel ) (Table 1, Fig 1&2)

Phase 3: Lactic acid fermentation

The strictly anaerobic lactic acid bacteria, especially the homofermentative one

convert the free sugars into lactic acid. (H. Danneret et al 2003). In the process

pyruvic acid (produced during glycolysis) is reduced to lactic acid while NADH2 is

oxidized.htt:/medinfo.ufl.edu/year2/mmid/bms5300/cases/a43a.html. This causes a

decrease in pH. (Fig 2, 4)

Fig 2 fermentation process (anaerobic microbe-LAB)

Phase 4: Stabilization phase

The presence of lactic acid inhibits further degradation for the remaining time of

preservation period. This is archived due to the low pH created in phase 3 stops plant

enzymatic activity and further microbial metabolism which preserves the forage as

silage assuming that oxygen is not allowed to penetrate the mass. (Limin Kung1995,

Marshal 1997)

Two other undesirable phases can also take place and cause important loss of dry

matter and forage quality in a silo:

1) Butyric acid fermentation by clostridia or butyric acid bacteria, which occurs if lactic

acid fermentation (Phase 3) fails to produce enough lactic acid to stabilize the silage.

Source http://www.forages.psu.edu/topics/hay_silage/preservation/silage_preserv/index.html

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2) Aerobic deterioration by molds and yeast that develop rapidly when well preserved

silage is exposed to oxygen after opening a silo.

Fig 3 deterioration process (clostridia)

Table 1.Some fermentation pathway in ensilage process (sources MacDonald 1995)

Lactic acid Bacteria Homofermentative

Glucose2 Lactic acidFructose 2 Lactic acidPentoseLactic acid + acetic acid (***)

Hetro fermentative Glucose Lactic acid+ Ethanol + CO2

3 Fructose Lactic acid + 2Mannitol + acetic acid + CO2

3 Fructose + glucose Lactic acid + 2Mannitol + acetic acid + CO2

Pentose Lactic acid + acetic acidClostridia

Saccharolitic2 Lactic acid Butyric acid + 2 CO2 + 2H2

Proteolitic Deamination

Leucine Isivaleric acid +NH3 + CO2

Lysine acetic acid + Butyric acid + 2NH3

Serine Pyruvic acid + NH3

Tryptophan Indolepropionic acid + NH3

DecarbocilationArginine Putrescine + CO2

Glutamic acid -aminobutyric acid + CO2 Histadin Histamine + CO2

Lysine Cadaverine+ CO2

Tryptophan tryptamine + CO2

Oxidation/reduction (stickland)Alanine + 2glycin 3 acetic acid + 3NH3 + CO2

Enterobacteria bacteriaGlucose actic acid + Ethanol + CO2

*** some researcher like Tomas James: homofementative bacteria are unable to ferment pentoses.

Source http://www.forages.psu.edu/topics/hay_silage/preservation/silage_preserv/index.html

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Graphic illustration of lactic acid bacteria pathway

Figure 4. The homofermentative pathway of lactic acid bacteria. Adapted from McDonald et al. (1991). In tomas 1997

Figus 5.The heterofermentative pathway of lactic acid bacteria. Adapted from McDonald et al. (1991) in Tomas 1997

Lactate Dehydrogenase

enzyme

Lactat Dehaydrogenase

enzyme

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3.2 Based on availability of oxygen the Silo

We can also classify the fermentation based on availability of oxygen the Silo in to two

main phases. (Ensiling process www.agric.gov.ab.ca/ $department/deptdocs.nsf/all /for4911 )

The fist or Aerobic phase

This occurs in the presence of oxygen. Under this conditions plant enzymes and

microorganisms consume oxygen and bum up the plant water-soluble carbohydrates

producing CO2 and heat.

The second or anaerobic phase

Begins when the available oxygen is used up through plant respiration, aerobic

bacteria cease to function. Then anaerobic bacteria begin to multiply rapidly and the

fermentation process begins. Predominately lacto~ bacilli species produce lactic acid

from the fermented plant material. Consequently lowers the pH of the silage and

fermentation completely ceases after 3 to 4 weeks and microbial growth is inhibited.

3.3 Other factors /Considerations

3.3.1 Plant Maturity and moisture Content

Proper maturity assures adequate fermentable sugars for silage bacteria and

maximum nutritional value for livestock.

High forage moisture levels at ensiling may cause silage effluent and favor

undesirable (clostridial) fermentations. Silages dominated by this type of fermentation

have a strong, rancid odor and are poorly consumed by cattle.

In contrast, ensiling forages when the moisture content is low (less than 50%) can

result in restricted fermentations, thereby producing less stable silages that have

lower lactic acid concentrations and less acidic (higher pH).

3.3.2 Nature of the plant

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The best silage is made from carbohydrate rich crops that contain more than two part

of carbohydrate to one part of protein like maize and sorghum (Martin J, 1995).

Marshal, 1997 also agreed that almost all crops can be ensiled provided that it

contains adequate level of moisture and sufficient amount of readily fermentable

carbohydrates.

Legumes are widely used ensiling material as they are rich in protein. However it

arises several problems due to their low content of sugars, high buffering capacity

(resistant to pH changes) and high moisture content. This leads to silage protein

degradability and also evidence of mold and spontaneous heating in these silages.

3.3.3 Silage additives

The main function of silage additives are either to increase nutritional value of silage

or improve fermentation so that storage losses are reduced. Response to additives

depend on what forage is being treated. http://ohioline.osu.edu/agf-fact/0018.html..

Effective silage fermentation must therefore promote high levels of lactic acid

production and create a low pH (3.8-4.2). (Maurice E.heath, 1985)

Based on Conail Keown description www.ruralni.gov.uk/index/publications press

articles_dairy / silage additives / additives can be grouped into four categories: (1)

inoculants; (2) enzymes; (3) substrate sources; and 4) inhibitors.

(1) Inoculants this is to ensure adequate quantities of lactic acid-producing bacteria

(www.vigortone.com/silageinoculants.htm). This aids in more efficient production of

lactic acid as the primary end-product which helps to lower the pH level quickly.

Weinberg & Muck, 1996 indicates the inoculant’s criteria to be Homofermentative

lactic acid bacterium, Acid tolerant, Ability to grow at temperatures up to 50°C.

Common LAB used in silage inoculants are: Lactobacillus plantarum, L. acidophilus,

Pediococcus cerevisiae, P. acidilactici, and Streptococcus faecium.

2. Enzyme additives: Various fiber degrading enzymes (xylanases, pectinases,

cellulases, hemicellulases) and starch degrading enzymes (amylase) have been

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used (Chen, et al 1994, Sheperd, 1994.) They degrade plant cell walls to reduce

the concentrations of neutral and acid detergent fiber in the silage and, at the

same time, release additional sugar, which is primary substrate for lactic acid-

producing bacteria. (Wayne Coblentz)

3. Substrate sources are primarily sugars, such as molasses, glucose, sucrose and

dextrose that provide additional substrate for lactic acid-producing bacteria. Acetic

acid has been proven to be the sole substance responsible for the increased

aerobic stability. Applied Environmental Microbiology.

4. Silage inhibitors have frequently been used in extremely wet silages where drying

conditions are often poor. Formic, propionic, hydrochloric and sulfuric acids, are

primarily organic acids that effectively sterilize the silage

(http://www.asab.org.uk/asa /adjudications/non_broadcast/) by inhibiting the fermentation

process and growth of all microbes in the silo (Mcdonald, 1995)

4. Conclusion

Good fermentation is desirable for proper storage and feeding. The necessary factors

are: anaerobic conditions, proper moisture, sufficient plant water-soluble

carbohydrates or sugars, proper bacteria (www. vigortone.com/silageinoculants .htm)

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Chemical changes are the result of plant enzymes activity (respiration and proteolysis)

and action of microbes depending on the absence or presence of oxygen.

Achieving an anaerobic environment as quickly as possible helps to limit respiration,

spontaneous heating, dry matter loss and mold development and improve bunk life

5. References

1. Applied Environtal Microbiology. 2003 January; 69(1): 562–567. Copyright © 2003, American Society for Microbiology)

2. Chen, J., M.R. Stokes, and C.R. Wallace. 1994. Effects of enzyme-inoculant systems on preservation and nutritive value of haycrop and corn silages. J. Dairy Sci. 77:501.

3. Conail Keown, www.ruralni.gov.uk/index/ publications /press_articles_dairy/ silage _ additives .

4. Danner H., M. Holzer, E. Mayrhuber, and R. Braun Acetic Acid Increases Stability of Silage under Aerobic Conditions, J. of Applied Environtal Microbiology. 2003 January; 69(1): 562–567.

5. Ensiling process www.agric.gov.ab.ca/$department/deptdocs.nsf/all/for4911

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6. Gillespie J.R, 1990,Modern livestock and poultry production 4th ed. Silage 707-709) 7. http://www.asab.org.uk/asa/adjudications/non_broadcast /)8. http://ohioline.osu.edu/agf-fact/0018.html .9. http://www.forages.psu.edu/topics/hay_silage/preservation/silage_preserv/index.html 10. Limin Kung, Jr. Silage Additives Profit Makers or Profit Takers? http://www. wcds.afns.

alberta.ca/Proceedings/1995/wcd95159.htm 11. Marshal H Jurgen , 1997.. Animal feeding and nutrition 8th Ed, Kendal /hunt publishing

comp. Silages pp 211-21612. martin JH, Leonard WH, Stamp DL, 1995 Principles Of Field Crop Production 3rd ed.,

Silage 231-239)13. Maurice E.heath, Robert F Barnes and Darrel S.Metcalfe, Forages the science and of

grass land agriculture, 4th ed 1985,iowastate University press USA14. Mc Donald et al, animal nutrition 5th ed., 1995 silage pp 451-464)15. McDonald, P., Henderson, A.R. & Heron, S.J.E. 1991. The biochemistry of silage second

ed. Chalcombe Publications in Lactic acid bacteria in silage – growth, antibacterial activity and antibiotic resistance Sandra Jansson MSc thesis 2005.

16. medinfo.ufl.edu/year2/mmid/bms5300/cases/a43a.html 17. Michel Wattiaux Introduction to Silage- Making Dairy Updates Feeding No. 502 University

of Wisconsin http://babcock.cals.wisc.edu18. Schroeder J.W. 2004 in http://www.ag.ndsu.nodak.edu/19. Sheperd, A.C. 1994. Effect of an additive containing plant cell wall degrading enzymes on

the nutritive value of corn silage for ruminants. M.S. Thesis. University of Delaware. 20. Silage inoculant in www.vigortone.com/silageinoculants.htm)21. Wikipidia , the free encyclopedia entry . WWW.wikipidia.ogr/wikiTomas J Rees, 1997 The

Development of a Novel Antifungal Silage Inoculant, Doctoral Research Thesis, Cranfield University. In www.brighton73.freeserve.co.uk/tomsplace/scientific/phd/ ntroduction /phd-intr.htm

22. Tremblay G. , G. Bélanger, K. B. McRae, and R. Michaud Can. J. Plant Sci. 81: 685–69223. Ulla Heiskari, Mauri Nieminen & Liisa Syrjälä-Qvist, Abstracts of posters presented at the

11th Nordic Conference on Reindeer Research, Kaamanen, Finland, 18-20 June 2001. (Published in Rangifer Report No. 5, 2001).

24. Wayne Coblentz, Principles of Silage making, www.uaex.edu/Other_Areas/pdf

INTERPRETATION AND USE OF SILAGE FERMENTATION ANALYSIS REPORTS

  By Limin Kung and Randy Shaver

 IntroductionFermentation analyses have long been used in university and industry research trials to assess silage quality. These analyses are now available for evaluating silage quality on farms through commercial forage testing laboratories. Analyses commonly included in silage fermentation reports are pH, lactic, acetic, propionic and butyric acids, ammonia, and ethanol. The purpose of this Focus on Forage is to answer the most frequently asked questions about the interpretation and use of these reports.

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What do these reports tell us about the fermentation process and silage quality? Collectively, data from a fermentation analyses can tell us whether an excellent, average, or poor fermentation has occurred. Based on theses analyses, we can usually make some educated assumptions about the kinds of microorganisms that controlled the ensiling process. In many, but not all cases, the fermentation that a crop undergoes can be explained by various crop factors such as moisture content, buffering capacity, and sugar content. However, management factors such as silo packing speed, silage pack density, type of additive used, chop length, silo management during storage, and silo management during feed-out can affect fermentation analyses. In some cases fermentation analyses can qualitatively explain poor silage nutritive value or low intakes, but they cannot be used to balance diets for cattle. Thus, they should always be used in conjunction with other standard chemical analyses (i.e. ADF, NDF, CP, RDP/RUP, NEL, NDF digestion, etc.). What does buffering capacity mean and what does it tell us about silage quality? Buffering capacity measures to what degree a forage sample will resist a change in pH. All forages have different buffering capacities. A fresh forage with a high buffering capacity will require more acid to reduce its pH than a forage with a low buffering capacity. In general, fresh legumes have a higher buffering capacity than do fresh grasses or corn.What are normal ranges for fermentation analyses? Table 1. Concentrations of common fermentation end products in various silages.

 

Item

Legume Silage, 30 - 40% DM1

Legume Silage, 45 - 55% DM

Grass Silage, 30-35%  

DM

Corn Silage, 30-40% DM

HM Corn, 70-75%

DMpH 4.3 - 4.7 4.7 - 5.0 4.3 - 4.7 3.7 - 4.2 4.0 - 4.5Lactic acid, % 7 – 8 2 - 4 6 - 10 4 - 7 0.5 - 2.0Acetic acid, % 2 – 3 0.5 - 2.0 1 - 3 1 - 3 < 0.5Propionic acid, % < 0.5 < 0.1 < 0.1 < 0.1 < 0.1Butyric acid, % < 0.5 0 0.5 - 1.0 0 0Ethanol, % 0.2 - 1.0 0.5 0.5 - 1.0 1 - 3 0.2 - 2.0Ammonia-N, % of CP 10 - 15 < 12 8 - 12 5 - 7 < 101DM = Dry matter.

What does a high pH value tell us about the fermentation process and silage quality? The pH of an ensiled sample is a measure of its acidity, but is also affected by the buffering capacity of the crop. Two samples may have the same pH, but different concentrations of acids. In general, legume silages have a higher pH than corn or other grass silages and take longer to ensile because of their higher buffering capacity.  Seldom do corn silages have a pH higher than 4.2. Such cases may be associated with extremely dry (>42% dry matter) silages that are overly mature or drought stricken. Because of its normally low pH (3.8), corn silage intake usually benefits from the addition of sodium bicarbonate prior to feeding to neutralize its acidity. Common reasons for legume silages having a pH higher than 4.6 to 4.8 include: ensiling at <30% dry matter (DM) which causes a

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clostridial fermentation, and ensiling at > 45-50% DM, which restricts fermentation. In the first example, a high pH due to clostridia is a definite indicator of an undesirable fermentation that has led to poor quality silage. However, in the second example, a high pH due to restricted fermentation is not always indicative of a poor fermentation or poor silage. But, silage from a restricted fermentation usually is unstable when exposed to air because insufficient amounts of acid were produced to inhibit secondary microbial growth. Some common reasons for a high silage pH are as follows:  - dry silage (> 50% DM)-silage not fully fermented due to early sampling time relative to harvest, cold weather during harvest, and slow or poor packing-Legume silages with extremely high ash contents (> 15% of DM) and (or) high protein content (> 23-24% CP)- silage with excess ammonia or urea- clostridial silages- spoiled or moldy silages- silages containing manure

What does a low lactic acid concentration tell us about the fermentation process and silage quality?Lactic acid should be the primary acid in a good silage. This acid is stronger other acids in silage (acetic, propionic and butyric) and thus usually responsible for most of the drop in silage pH. Secondly, fermentations that produce lactic acid result in the fewest losses of dry matter and energy from the crop during storage.Some common reasons for low lactic acid content are as follows:Extremely wet silages (< 25% DM), prolonged fermentations (due to high buffering capacity), loose packing, or slow silo filling can result in silages with high concentrations of acetic acid (>3 to 4% of DM). In such silages, energy and DM recovery are probably less than ideal. Silages treated with ammonia also tend to have higher concentrations of acetic acid than untreated silage, because the fermentation is prolonged by the addition of the ammonia that raises pH.   A new microbial inoculant (Lactobacillus buchneri) designed for improving the aerobic stability of silages causes higher than normal concentrations of acetic acid in silages. However, production of acetic acid from this organism should not be mistaken for a poor ermentation and feeding treated silages with a high concentration of acetic acid does not appear to cause negative effects on animal intake.

What affect does silage with a high acetic acid concentration have on animal performance? The effect of high concentrations of acetic acid (> 4 to 6% of DM) in silages fed to animals is unclear at this time. In the past, some studies can be found where DM intake was depressed when silage high in acetic acid concentration was fed to ruminants. However, the depression in intake to high acetic acid in the diet has not been consistent. There has been speculation that decreased intake may be actually due to unidentified negative factors associated with a poor fermentation and not to acetic acid itself. For example, in recent studies, animals showed no indication of reduced intake when fed silages high in acetic acid due to inoculation with the bacteria Lactobacillus buchneri, which was added to improved aerobic stability.  

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If a producer has intake problems due to silages with excessively high acetic acid (> 5 to 6% of DM), the amount of that silage should be reduced in the TMR. Other alternatives for managing these silages include: aerating the silage for a day to volatilize the acetic acid, removing the silage and then gradually reincorporating it back into the diet over a 2 –3 week period, and partially neutralizing the silage with sodium bicarbonate prior to feeding (about 0.5 to 1% addition on DM basis).  What does silage propionic acid concentration tell us?  Most silages contain very low concentrations of propionic acid (< 0.2 to 0.3%) unless the silage is very wet (< 25% DM). In silages with more typical concentrations of DM (35 to 45% DM), concentrations of propionic acid may be undetectable.  Are there additives that can increase the propionic acid concentration of silage?  Biological additives that theoretically increase the propionic acid concentration of silage usually contain bacteria from the Propionibacteria family. However, research suggests that these organisms are usually unable to compete in normal silage environments and are thus, usually ineffective.  Chemical additives containing propionic acid are more effective for increasing the concentration of this acid in silages. These additives can range markedly in their percentage of active ingredients but most mainstream products will increase the concentration of propionic acid at ensiling from 0 to about 0.15 to 0.30% (DM basis) if added at 2 to 4 lb per ton of wet (~35% DM) silage.  What does a high butyric acid concentration tell us about the fermentation process and silage quality?  A high concentration of butyric acid (>0.5% of DM) indicates that the silage has undergone clostridial fermentation, which is one of the poorest fermentations. Silages high in butyric acid are usually low in nutritive value and have higher ADF and NDF levels because many of the soluble nutrients have been degraded. Such silages may also be high in concentrations of soluble proteins and may contain small protein compounds called amines that have sometimes shown to adversely affect animal performance.What affect does silage with high butyric acid concentration have on animal performance?  High butyric acid has sometimes induced ketosis in lactating cows and because the energy value of silage is low, intake and production can suffer. As with other poor quality silages, total removal or dilution of the poor silage is advised.  What does a high ammonia concentration tell us about the fermentation process and silage quality?  High concentrations of ammonia (>10 to 15% of CP) are a result of excessive protein breakdown in the silo caused by a slow drop in pH or clostridial action. In general, wetter silages have higher concentrations of ammonia. Extremely wet silages (< 30% DM) have even higher ammonia concentrations because of the potential for clostridial fermentation. Silages packed too loosely and filled too slowly also tend to have high ammonia concentrations.

What affect does silage with high ammonia concentration have on animal performance?

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Theoretically, high amounts of ammonia (by itself) in silage should not have negative effects on animal performance if the total dietary nitrogen fractions are in balance. However, if the high ammonia contributes to an excess of ruminally-degraded protein (RDP), this could have negative consequences on milk and reproductive performances. Blood or milk urea nitrogen can be used as an indicator of excess RDP. Often times, silage with high concentrations of ammonia coupled with butyric acid may also have significant concentrations of other undesirable end products, such as amines, that may reduce animal performance.

What is a high ethanol concentration and what does it tell us about the fermentation process and silage quality?  High concentrations of ethanol are usually an indicator of excessive metabolism by yeasts. Dry matter recovery is usually worse in silages with large numbers of yeasts. These silages are also usually very prone to spoilage when the silage is exposed to air. Usual amounts of ethanol in silages are low (< 1 to 2% of DM). Extremely high amounts of ethanol (> 3 to 4% of DM) in silages may cause off flavors in milk.   What affect does silage with high ethanol concentration have on animal performance?  We do not know the level at which ethanol becomes a problem in dairy cattle diets. Most ethanol that is consumed is probably converted to acetic acid in the rumen.

Can silage fermentation reports be used to help in balancing of diets for dairy cattle? We know of no acceptable method that uses silage fermentation analyses for balancing nutrient requirements for dairy cattle.

How can silage fermentation reports be used for troubleshooting animal performance problems?  Assuming that all nutrients are balanced properly in the diet, silage fermentation reports may be able to identify the reason for intake or performance problems.

Can silage fermentation reports tell us whether or not a silage additive worked?Usually not, unless done in a well controlled research trial. However, one might be able to tell if a propionic acid product were added to silage since most silages typically are low in this acid. If silage was treated with about 2 lb/ton of fresh forage using a buffered propionic acid product, one might be able to detect the increase in this acid. Most silages have < 0.15% propionic acid.

How should silage samples be taken for fermentation analyses?If your goal is to evaluate what animals are being fed, then samples should be reflective of this by sampling at feeding.If your goal is to see what type of fermentation process the silage went through, then collect a sample that is a fresh as possible and that has not been exposed to air (typically at least 8 to 10 inches below or beyond the face). How should silage samples be handled and shipped for fermentation analyses?  

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For chemical fermentation analyses, samples should be frozen immediately after being taken, then shipped preferably on ice in a cooler by a next day delivery service. Ship at the beginning, not end of the week so samples will not be held up during the weekend.  What commercial testing laboratories perform silage fermentation analyses? To the best of our knowledge, as of August 2001, the following commercial forage testing laboratories perform fermentation analyses:

Gas chromatography Cumberland Valley Analytical Services Maugansville, MD Contact: Ralph Ward, (301) 790-1980, cvas@intepid.net

Near-infrared Rock River Laboratories Watertown, WI Contact: Don Meyer, (920) 261-0446, rrllab@execpc.com

High-performance liquid chromatography Dairyland Laboratories Arcadia, WI Contact: Dave Taysom, (608) 323-2123, dtaysom@dairylandlabs.com

Current information on analytical costs and sample turn-around time is best obtained directly from the individual labs.

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