There are many types of microbes occurring naturally on forage crops in the field, their populations varying with the specific climatic features of the year, crop management practices and the stage of maturity of the plant. These bacteria, yeasts and molds are simply waiting for the right conditions for them each to grow and multiply. Influencing the situation to get the right microbes to dominate at the right time is the difference between quality silage and compost.
The "good guys" in the war for an efficient — and effective — ensiling fermentation, which drives a successful ensiling process, are homolactic acid bacteria. These microbes contribute to a rapid pH drop to below 5.0, preventing "bad" fermentations and shutting down the plants own auto-degradation process. However, these bacteria may often not be naturally present in sufficient numbers to create good silage.1
Spoilage yeasts also occur naturally in varying numbers on all pre-harvest crops as part of the mixed microbial community described above. If these yeasts become dominant, they can start the process of aerobic deterioration — raising the forage pH, which allows for further spoilage by molds and bacteria. These "bad guys" in the microbial fermentation "war" are also the reason producers can see instability during feed out. There are also naturally occurring aerobic bacteria that can grow while oxygen is present causing considerable nutrient loss and preventing a rapid pH drop.
Crops with high protein content and lower fermentable sugars — such as clover, alfalfa, grasses and some small grain cereal silages — are even more at risk, since they tend to be cut closer to the ground. When crops are cut close, there"s a higher risk for soil contamination. Soil can contain very high numbers of spoilage bacteria like clostridia and enterobacteria, both of which can result in silages with feeding issues. Many consider clostridial silage to be the worst possible result: The silage will be wet, dark and smell foul and should not be fed to pregnant or transition cows and only fed in limited amounts to lactating dairy cows (to maintain intake of butyric acid below 50 grams per head per day.
When unstable and potentially moldy feeds are ingested by cattle, the consequences on rumen function and performance are disastrous. They can push a cow or steer with borderline rumen function into metabolic issues such as Sub Acute Ruminal Acidosis (SARA) and can also contribute to health and fertility problems.
To win the microbial war in your silages, it"s important to use research-proven forage inoculants containing fast acting, efficient homolactic acid bacteria. This loads up your silage with an army of these good microbes and helps ensure the right balance is in place. Additionally, inoculants that contain Lactobacillus buchneri 40788 at an effective dose in addition to the homolactic bacteria can help address stability challenges at feedout, saving DM, minimizing associated health and fertility issues and maximizing profitability.
1 McDonald P., Henderson A. R. & Heron S. J. E. 1991. The Biochemistry of Silage, Chapter 4, Microorganisms.