Learn how careful grassland management, optimal harvesting, effective compaction and the right biological inoculant can improve grass silage quality, palatability, feed intake and dairy cow performance.
Grass silage constitutes a vital component in providing essential nutrients to dairy cattle and other ruminants across the globe. In certain agricultural systems, it may account for over 50% of the roughage in livestock rations. Its quality and taste are of particular importance to achieve the necessary feed intake and performance of our modern high-yielding dairy cattle. However, the production of high-quality grass silage is a delicate and multifaceted endeavor, necessitating precise management, particularly concerning grassland stewardship and the timely and meticulous execution of harvests.Grass silage constitutes a vital component in providing essential nutrients to dairy cattle and other ruminants across the globe. In certain agricultural systems, it may account for over 50% of the roughage in livestock rations. Its quality and taste are of particular importance to achieve the necessary feed intake and performance of our modern high-yielding dairy cattle. However, the production of high-quality grass silage is a delicate and multifaceted endeavor, necessitating precise management, particularly concerning grassland stewardship and the timely and meticulous execution of harvests.
The process begins with the discerning selection of seed varieties, ensuring their suitability for the unique environmental conditions of each region. For instance, planting drought-sensitive varieties in areas prone to water shortages is decidedly imprudent. Moreover, the farmer’s specific objectives must be factored into the decision-making process. Alfalfa, for example, is a superior protein source that exhibits drought resilience but demands careful attention during harvest to preserve its nutrient-dense leaves, which are prone to significant loss if handled the wrong way. While wildflowers such as dandelions and poppies may lend aesthetic appeal to a meadow, they contribute little to silage quality and, in fact, diminish its overall nutritional value. These examples underscore the critical importance of rigorous meadow management following seeding. Especially in conditions of low pH levels, undesirable grass species and herbs thrive increasing their share of the vegetation, significantly reducing the prevalence of beneficial and desirable grass varieties. The target percentage of desirable grasses should be 60% or above while herbs should only account for 15 to 20%.
For example, molehills—although ecologically beneficial—pose substantial risks to feed quality and safety by increasing the likelihood of contamination from Clostridia originating in the soil. Despite reducing the ecological benefit of a high-variants meadow, the overarching objective should be the maintenance of as pristine a meadow as possible to maximize the nutrient density of the resulting silage. This can only be achieved through precise soil management, which includes regular soil testing and tailored fertilization practices.
As the grasses mature, the time of the harvest gets closer. Timing the harvest correctly is necessary to strike an optimal equilibrium between quality and yield, while accounting for weather conditions, which in its entirety presents a complex challenge. In general, it is advisable to initiate harvest prior to ear emergence and cut not lower than 5 cm (2 inches) above ground.
Contrary to some prevailing beliefs, cutting the grass excessively close to the ground may increase immediate yield but significantly reduce subsequent harvests due to diminished photosynthetic capacity. This issue can be exacerbated by water deficits and high solar radiation, both of which place additional strain on the plant and future cuts. On top of that, cutting grass excessively short can result in a shift of the vegetation composition reducing the feed value of the harvested grass silage.
The target dry matter content during wilting is between 28% and 35%. As such, considerations of solar radiation and other weather variables should guide harvest scheduling to ensure that the grass silage achieves the optimal dry matter content, thereby avoiding the production of excessively wet or dry or hay-like silage, which poses a risk for undesirable fermentation on the one side and reheating and/or mold growth on the other side.
Many farmers commit the error of overly aggressive raking, which disturbs the soil surface and introduces unnecessary much more dust (crude ash), as well harmful soil-dwelling bacteria into the silage.
This not only compromises the nutritional value of the silage but also reduces its palatability. Regular recalibration of rake settings is imperative to maintain the highest standards of silage production. The ideal chopping length should as an optimum be between 1 and 4 cm and should not exceed that. Cuts that are longer than 4 cm diminish the ability to compact the silage effectively, compromising its post-opening aerobic stability, which facilitates mold growth. As the dry matter content rises and the grass becomes more fibrous, shorter chop lengths should be employed to enhance compaction and reduce the risk of secondary fermentation, or reheating.
Once harvested, compaction is of paramount importance. Regrettably, many farmers fail to accord this step the attention it warrants, leading to significant nutrient losses. The weight of the compaction machinery for grass silage should exceed one-third of the total hourly harvest volume in tons. Insufficient compaction raises the risk of reheating and mold growth, which in turn compromises the overall quality of the silage as described in the trials of Souza et al. 2003. In their trial, they demonstrated that a mere 25% reduction in compaction resulted in an increase of over 1 log in mold and yeast proliferation following opening. Consider the following real-life case: A farmer reported that his silage became excessively heated upon opening.
He noted that, despite following the same harvesting practices that had proven successful in past years, he encountered this reheating issue. When asked for more details, he revealed that he had recently acquired a new forage wagon to replace his old one. This new (and particularly larger) forage wagon resulted in an elevated hourly harvest volume exceeding the capacity of his compaction machinery. This incident highlights the importance of aligning the compaction machinery's weight with the hourly harvest volume based on the used machinery to ensure proper compaction.
Another crucial consideration in silage production is the thickness of individual layers. If the layers exceed 20 cm prior compaction, the effectiveness of the compaction process is diminished, increasing the likelihood of reheating. Upon completion of the filling process, the silo should be sealed immediately and airtight with a plastic film, secured by the additional cover with a bird net and additional weight to prevent air infiltration.
Despite adhering to all above-mentioned best practices, the production of high-quality silage is not guaranteed. Grass, like all plants, hosts a diverse array of microorganisms, some beneficial and others harmful. These microorganisms consume the silage’s nutrients, diminishing its quality. Certain bacteria, such as Clostridia, can decompose proteins into low-value ammonia nitrogen or produce butyric acid, significantly impairing the palatability of silages. Others may generate excessive acetic acid, further reducing its appeal. A shared characteristic of these bacteria is their susceptibility to low pH levels. Therefore, rapid acidification and pH reduction are crucial to inhibit their activity.
The use of biological silage inoculants containing lactic acid bacteria is highly recommended to achieve this. These added lactic acid bacteria play a dual role: they occupy niches on the plant material to prevent the growth of undesirable microbes, and they produce organic acids that suppress harmful microorganisms. Lactic acid bacteria in inoculants can be classified into homofermentative and heterofermentative types. Homofermentative bacteria are particularly important in grass silage, as they rapidly lower the pH through lactic acid production, effectively halting the proliferation of undesirable fermentation agents. Heterofermentative bacteria, which also produce acetic acid, are useful in suppressing yeast growth after the silage pit is opened, reducing the risk of reheating and secondary nutrient loss. Currently, no single silage inoculant on the market is suitable for all crop types and harvest conditions. Each product offers specific features tailored to particular circumstances. It is, therefore, advisable to select an inoculant suited to the specific conditions at hand.
Wetter grass silages benefit from inoculants containing a high numbers and proportion of homofermentative bacteria, to produce enough acid to counteract the silage’s increased water content and buffering capacity. On the other hand, drier grass silages are better served by heterofermentative bacteria due to their ability to produce acetic acid, which suppresses yeast growth after the silage pit is opened as dried grass silage are at risk for a secondary fermentation. For sugar-rich grass silages with normal dry matter content, rapid acidification and protection from secondary fermentation, such as reheating, are crucial. In such cases, combination products that leverage the advantages of both homo- and heterofermentative lactic acid bacteria are ideal. For farmers seeking simplicity, “all-purpose” inoculants are the preferred choice, as they provide versatility across various conditions. However, for optimal silage conservation, a more tailored approach is recommended. The lower part of the silage pit should be treated with a pure homofermentative product to ensure rapid acidification and effective preservation. In contrast, the upper part should be treated with a pure heterofermentative product to suppress yeast growth and prevent reheating. This diversified strategy ensures that each region of the silage pit receives the most suitable bacterial type for its specific needs, enhancing overall silage quality and palatability. Only after completing all necessary steps prior to harvesting and during harvest, one can say one has done all everything humanly possible to achieve a high-quality silage to feed the high-yielding dairy cows.
