This is the strongest acid produced during a silage fermentation so produces the fastest pH fall, from about pH 6 in the fresh forage to around pH 3.8-4.5 (depending on the crop and DM) in the final silage, as well as the lowest fermentation losses. In less efficient fermentations some of the lactic acid is replaced by the weaker acetic acid and/or neutral ethanol which results in a slower pH fall.
If the initial fermentation is dominated by heterofermentative lactic acid bacteria, fermentation acidification is slower and less efficient fermentation due to the production of weaker acids (eg acetic acid), non-acids (eg ethanol) and carbon dioxide. This means that more sugar will be required to achieve the same final pH value and fermentation losses will be higher.
Indigenous plants and food security: South African case study
If sugar is limiting a stable pH value may never be reached. This can allow other very undesirably bacteria, eg clostridia, to take control, changing a poor fermentation into a very bad fermentation with a much reduced nutrient value and high losses.
The slower fall in pH value also means that there will be a greater breakdown of proteins, mainly due to continued plant enzyme activity.
A rapid pH fall reduces protein breakdown and reduces the activities of undesirable bacteria, minimising the production of highly undesirable products such as butyric acid and ammonia which would reduce silage palatability. The lactic acid bacteria in inoculant additives aimed at helping with the initial fermentation are homofermentative.
A high proportion of lactic acid in the total acids and a low level of ammonia are both indicators of good fermentation.
