Forage quality and consistency rank near the top of every dairy producer’s list as key influences on farm profitability. As herds have grown in size, correspondingly so has the use and size of bunkers and piles to store forage.
Indisputably, harvesting larger quantities of forage puts multiple stresses throughout the forage system — from cropping to feeding. Forage density and pile construction not only are critical to ensuring optimal forage quality and consistency but also can play a substantial role in silage safety by minimizing the risk of avalanching.
Much has been written on the need for a high forage density to minimize oxygen infiltration throughout the forage mass during filling, storage, and feedout. Limiting oxygen infiltration controls plant and microbial processes, thus enhancing fermentation and reducing spoilage. Numerous studies have identified key factors influencing forage density.
These factors include the number and weights of tractors, the time the tractors are on the pile, initial forage spreading thickness, delivery rate of the forage to the bunker or pile, and forage dry matter content. The final component of forage density is pile depth and forage location relative to the top of the pile. As pile or bunker height climbs to 10 feet, 20 feet, or greater in height, the sheer weight of the forage above will ensure higher densities the closer forage is to the bottom of the pile.
Think snow
Although high forage densities will benefit fermentation efficiency and consistency, what hasn’t been discussed extensively is the very real effect proper packing and pile formation has on silage safety. As piles and bunkers climbed in height, so has the potential for silage to avalanche. At the very least, these avalanches can result in several days of feed being exposed to oxygen, resulting in the loss of valuable nutrients and dry matter. The documented outcome is reduced milk production and spoiled forage that is often implicated in cow health issues.
More alarming is the elevated risk of human injury and death caused by forage piles caving or avalanching. Such occurrences have certainly been noticed by entities such as the Occupational Safety and Health Administration (OSHA) and insurance companies. While any large pile is at risk for avalanching, there are some preventative methods that can be taken to reduce avalanche occurrences.
The study of how avalanches form and what triggers them has been extensively studied in areas where large amounts of snow are deposited on steep mountain slopes. In general, any slope greater than 30 degrees has an enhanced danger of avalanching. Two other factors making snow prone to avalanching include a lack of cohesiveness between layers of snow and differences in “snow packing.” Imagine a light dry snow layer covered by a dense, icy layer of snow. The two very different properties of the snow result in an area of weakness. It is this area of weakness that is one of the risk factors that can trigger a snow avalanche.
So how does this play into silage density?
Keep layers thin
A key factor necessary to reach an optimal density goal is spreading and packing forage in thin layers. Recommendations based on several studies advise to push and pack silage in 4- to 6-inch layers. Admittedly, this requires a great deal of skill, patience, and practice on the part of the push and pack tractor operator.
Larger and more powerful forage choppers have resulted in extremely high forage delivery rates to the pile during harvest, particularly for corn silage. With high delivery rates, it is not uncommon for the push tractor operator to revert to “survival mode” and begin pushing large amounts of forage onto the pile. Simply put, thin layers are sacrificed to keep up with the chopping crew.
Forage spread at higher layer depths, often a foot or more, can create a similar scenario to our snow avalanche. Less dense forage under more densely packed forage creates an area of weakness. This potentially leads to a lack of cohesiveness, but unlike snow there are other more serious ramifications in silage with an escalating risk of avalanching over time.
As discussed earlier, oxygen is our enemy from the time the forage enters the pile continuing throughout storage and feedout. If a portion of the pile is not properly packed, a delayed or inefficient fermentation can result that initiates the spoilage process. This leads to a loss of dry matter sometimes noticed by excessive heating of the forage. This loss of dry matter reduces density.
While it may be difficult to “see” forage loss, imagine forage heating or spoiling similar to burning a piece of paper. Burning the paper results in less mass and lost dry matter, creating an area of weakness. Additional spoilage changes the properties of the forage, which can lead to less cohesiveness, magnifying the area of weakness.
Unfortunately, additional stress is placed upon opening the pile. Exposing a forage face allows protective gases, formed during fermentation, to leave the spaces between forage particles.
Oxygen is then drawn into the silage through the process of diffusion. The less dense a forage is packed, the more and further oxygen can infiltrate, perpetuating the area of weakness. Eventually the forage may succumb to the effects of gravity and fall. This may be evidenced as a “slab” avalanche down the side of a pile, or silage simply tumbling off the feeding face.
Cohesiveness needed
Understanding the principles of how spoilage can initiate and contribute to avalanching gives valuable insight into one of the more common observations of falling forage: It often occurs at the interface between different crops or years of forage within a pile or bunker.
Optimal feedout rates are recommended to try to keep ahead of this destructive process. While feedout rates can mitigate the nutritive losses during feeding, it will not prevent some spoilage from happening when fresh forage is piled against the previous fermented crop.
No matter how quickly the forage is covered by the incoming crop, some degree of spoilage does happen. The introduction of air leads to dry matter loss in the fermented feed. Add in a lack of bonding and cohesiveness or “tying in” to the old forage and the problem is intensified. That lack of cohesiveness and loss of dry matter elevates the risk of avalanching.
On large piles or bunkers, it nearly guarantees silage to break off once the feeding face approaches the split. Operators have tried to minimize the risk of avalanching by facing the older forage at a 45-degree angle prior to bringing in the new forage. Usually, this simply prolongs the area susceptible to avalanching as the same principles are at work, albeit with a reduced angle.
To try to minimize the air exposure on the fermented face some have tried quickly covering the exposed face. However, pushing large amounts of silage in a small area often violates laying forage in thin layers and it simply compounds the problem.
The only viable solution to the above problem is to put different crops into separate piles or bunkers. For corn silage, different crop years are put in separate piles. This has successfully been implemented on several farms.
A strong case can be made for the merits of separating crops based on cow productivity and health benefits alone. Certainly, there is expense in expanding the footprint of the storage structure, and careful planning is needed when evaluating forage inventories and incoming forage. However, the upside of a safer feed center outweighs the expense and has been the deciding factor for farms that have implemented such a practice.
Check cover integrity
Occasionally, a pile will suddenly avalanche for no apparent reason. Careful examination will sometimes reveal a seam in the plastic cover that has either pulled apart or was placed counter to water flow, allowing rain and oxygen to infiltrate and spoil the forage over time.
Proper instruction to allow for several feet of overlap on seams and making sure seams don’t catch and allow water into the pile is imperative to proper pile covering and storage. Regularly checking for holes and damage to plastic, particularly after severe wind, storms, or hail should be a part of the farm’s routine.
Forage safety is a value everyone needs to be invested and committed to. Renewed focus needs to be put on proper pile construction and packing density, particularly as it pertains to laying forage in thin layers. With silage depth playing a role in large piles, adding additional weight or another pack tractor operator toward the top 10 feet of the pile can help concentrate efforts where the pile is most vulnerable to avalanching. Underscoring the importance of pile construction and packing density has a very real influence on the safety of people working around them all year long.
The author wishes to thank Bob Headrick, a custom forage operator in California, for his insights that were included in this article.
This article appeared in the November 2017 issue of Hay & Forage Grower on pages 27 and 28.
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