Lactic acid, volatile fatty acids (VFA) and alcohol in silage fermentation process
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Volatile fatty acids are the main products in the fermentation process of silage materials, some of them are harmful and some are useful. In general, the most important volatile fatty acids that affect the quality of a silage are as follows:
A-lactic acid:
Lactic acid is considered one of the important indicators in the diagnosis of a good fermentation in the silage process. Lactic acid alone should account for 70% of the total acids in the silage, this amount is equivalent to 4-5% of the dry matter. It is desirable in silage. High-quality silage fodder that has dry material suitable for ensiling, is not devoid of dissolved sugars, its ensiling process is carried out in completely anaerobic conditions, its pH often reaches below 4.5 within just a few hours, and finally the result of fermentation is Its aeration is the cold process of silage, the final product (silage) is obtained from it. It is accompanied and due to these factors, the amount of lactic acid in the environment of the silo increases, and as a result, the quality of the produced silage improves significantly.
Below we list the most important bacterial species that produce lactic acid in silos:
1- Streptococcus (S.faecium)
2- Enterococcus
3- Lactococcus
4- Leuconostoc
5- Pediococcus (P.pentacocus, P.cerevisea)
6- Lactobacillus (L. buchenari, L. acidilacti)
7- Bifidobacterium
8- Plantarium
Note: In harvested silage, the bacteria producing lactic acid are 1000 times less than their aerobic competitors such as fungi and enterobacteria. When the ensiling conditions are completely anaerobic and the dry matter of the forage is favorable, then there is room for the growth of harmful bacteria. It did not occur in the silo and lactic acid producing bacteria will be able to grow and multiply with this small population.
B- Acetic acid:
When the pH is higher than 4.5, enterobacteria grow and multiply and produce acetic acid. Also, when the time to reduce the pH below 4.5 is prolonged, in that case the nutrients for the production of high-quality silage are reduced and the amount of acetic acid production in
The environment of the silo increases. The smell of sourness, the pungent smell of vinegar and the yellow color (pale color) of the produced silage indicate a high amount of acetic acid in it. These characteristics are revealed when the amount of acetic acid is more than 50% of the silage dry matter increase. As the amount of acetic acid increases, silage consumption will decrease and its taste will not be pleasant for cows.
What should we do with this problem?
First of all, we should provide the conditions of the silo in such a way that we do not face this problem. For this, fodder with the optimal dry matter percentage (for fodder corn, the minimum optimal dry matter is 25%, for withered alfalfa, 28%, and for wet sugar beet pulp, 22% and make the ensiling conditions completely anaerobic (the best conditions are found in the polyethylene bags of silage machines).
If the amount of silage acetic acid is high, mix it with higher quality silage to reduce the amount of poor quality silage in the ration. In other words, use less quality produced silage in the ration.
Air the silage containing a lot of acetic acid for a day before use.
In order to neutralize the acetic acid of silage that smells like vinegar, use sodium bicarbonate at a ratio of 0.5 to 1% of the dry matter consumed.
C- Butyric acid
Butyric acid is produced by several species of Clostridium. Its main source is soil and animal manure. The spores of this microbe may sit on the silage and in the conditions where the silage is not completely anaerobic, its growth and reproduction begin. High amounts of butyric acid in silage (more than 0.5% of dry matter) have the following adverse effects:
* Reduction of silage consumption by livestock
* Health complications caused by the increase of ketones in the blood and the occurrence of ketosis in cattle
* The presence of butyric acid in silage brings a pungent smell, the smell of wind and the smell of rotten fish to our nose.
The main reasons for the high level of butyric acid in silage are, as we said, the contamination of the fodder with soil and animal feces. In addition, the fodder contains low amounts of energy-generating substances and the absence of soluble sugar in the environment, and most importantly, excessive moisture in fodder corn. (less than 22% of dry matter) is one of the factors of the presence of butyric acid in silage as an undesirable product of the fodder ensiling process.
d-ethyl alcohol (ethanol)
Ethyl alcohol is produced by bacilli bacteria (with silages) and alcohol-producing yeast. Usually, when forage ensiling is done under anaerobic conditions, the amount of ethanol does not exceed one to two percent and does not cause a problem. When air penetrates into the silo, the risk of mold growth by bacilli microbes increases greatly. After opening the silo and its proximity to the air, and if the silage is not used for a short period of time, the yeast will grow quickly and due to the presence of oxygen in the environment, the produced silage will spoil quickly (fermentation of silage tannin in an aerobic environment). Smelling the smell of alcohol is a sign of very weak and unacceptable fermentation.
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