*3.3.2 Laboratory measurements of the silage*

1. **Lactic acid**: the goal of good fermentation is to maximize the production of lactic acid.

Lactic acid is the strongest fermentation acid in the fermentation process, which has the best effect in reducing pH value. Rapid reduction of pH value helps to reduce protein decomposition, increase the acidolysis of hemicellulose, and reduce other useless microbial activities. The high ratio of lactic acid and lactic acid/acetic acid indicates that good fermentation has taken place.


### **Table 1.**

*The sensory evaluation of silage.*

### **Figure 3.**

*The surface morphology of the starting material and the resulting silage.*

2.**Acetic acid**: the formation of acetic acid usually occurs in the first 2 to 3 days of silage.

When the pH value drops below 5.00, the *Lactobacillus* begins to grow and takes over the fermentation process. Therefore, in typical silage, the production of acetic acid is helpful to activate the production of lactic acid. In the process of opening cellar to take silage, the degradation of lactic acid by yeast can also produce acetic acid. The concentration of acetic acid is usually low (<3%). It has some antifungal properties, which help to prolong the retention time of the silage.

3.**Propionic acid**: usually found in only a small proportion with silage.

A high level of propionic acid with silage indicates a large error in some places. It is normal that propionic acid is higher when adding propionic acid additive.

4.**Butyric acid**: butyric acid is produced by *Clostridium perfringens*. If the silage is too wet (DM <30%), the bacteria will multiply.

In wet silage, the acid produced by *Lactobacillus* may not be enough to reduce the pH value to prevent the growth of *Clostridium*. *Clostridium* can also ferment lactic acid to produce butyric acid and decompose amino acid to produce excessive ammonia. Both of these effects lead to an increase in pH and further deterioration of silage.

The results of the author's study are as follows: The pH value (4.22), pretreatment time (4 weeks), and the content of lactic acid in dry corn stover silage (4.32%) should be considered as important indicators of the success of microbial ensiling [26].
