THE WORK AT THE BUNK MATTERS
It’s the time of year when, hopefully, everyone is deep into harvesting corn silage or has already finished. It goes without saying that the work doesn’t end once the feed has been delivered to the bunk. The timing of harvest is certainly important for determining the quality of forage ensiled and ultimately fed to the cow, but how the forage is delivered and packed into the bunk can have a major impact on how well that quality is preserved. The goal of ensiling is to remove as much oxygen as quickly as possible to create an optimal environment for fermentation. Oxygen, aerobic microorganisms such as yeasts and molds, available substrates such as sugars and organic acids, and temperature all influence the amount of dry matter and nutrient loss that can occur during storage and feedout.
One of the primary goals of ensiling should be to achieve an adequate silage density. A common recommendation of a minimum optimal density on a dry matter (DM) basis is 240 kg DM/m3 (15 lb. DM/ft3), or on an as-fed basis (AF) 700 kg AF/m3 (43/7 lb AF/ft3) depending on the DM. If DM increases, then the packing density must increase. The reason for achieving an optimal density is to reduce the porosity of the bunk face, with an optimal percentage being below 40%. Porosity is the void spaces between the forage particles, which provide pathways for oxygen to infiltrate. Consequently supporting microbial activity, producing more carbon dioxide and heat, and decreasing forage quality.
This leads to the question of how to achieve adequate density, and this is where the commonly cited “rule of 800” can be used. For every ton of silage delivered to the bunk per hour, 800 lb. of packing weight is needed. Therefore, if 50 tons/hour is delivered to the bunk, 40,000 lb. of packing weight is needed. The table above shows an estimate of weight needed based on a range of silage delivery rates. Knowing the amount of weight needed to achieve an adequate bunk density is just one piece of the puzzle. The weight of packing equipment available should meet the amount of forage delivered per hour and the amount of time needed to pack that forage. When too much forage is delivered the amount of packing weight and time available for each ton of forage decreases, and density can suffer. One method is to increase packing weight. This may be achieved by adding weight to an individual tractor or increasing the pieces of equipment packing on the bunk. The amount of forage packed at one time can influence the storage density as well. It may be useful to consider decreasing the thickness of the layer that’s packed each pass across the bunk.
What might be even more important to consider is the DM % of the forage being ensiled; the recommendation for ensiling corn is 32-38%. If the silage is too wet it can cause nutrient losses through seepage and poor fermentation. On the other hand, if it’s too dry this can prevent proper packing, leaving air pockets which increase the porosity of the bunk and allows for increased microbial activity. Therefore, the amount of weight needed to achieve the optimal density and ultimately porosity greatly depends on the DM % of the forage being ensiled. Ultimately, the quality of forage put in the bunk, and how it is handled once there, impacts the quality of the forage that the cow will consume.
— Victoria Blaney
