Oxygen is the enemy of high-quality silage, so it is vital to pack the silage efficiently to drive air out. Getting the oxygen out is so important because while it is present aerobic spoilage microbes can grow, reducing silage quality and causing dry matter (DM) and nutrient losses, and because it delays the start of the anaerobic ensiling fermentation.
Poor packing can cause problems at ensiling and all the way to feedout. Packing literally squeezes air (oxygen) out of the silage. Done properly, this will help limit the growth of aerobic spoilage yeasts, so that numbers are kept below the 100,000 CFU/ g maximum threshold, recognized by University advisors as the level that will mean unstable silage at feedout.
The two management control points with the biggest impact on silage density are filling layer depth, recommended no greater than 6", and packing effort. Poor packing leads to increased silage porosity, which allows greater air ingress at feedout, which in turn results in additional spoilage and DM losses.
The packing density achieved on commercial operations has been shown to vary considerably, as shown on Table 1.
The minimum recommended pack density is 44 pounds per cubic foot on a fresh weight basis at 34 % DM. To properly calculate the packing density, a calculator spreadsheet can be found online at http://fyi.uwex.edu/forage/harvest/ that helps producers estimate the average density of forage in various storage units. As a rough "rule of thumb" the amount of packing tractor weight (in lb.) required to achieve good packing can be calculated by multiplying the number of tons of silage brought to the pile or bunker per hour by 800. For example, if 100 tons of silage are being brought in per hour, the packing tractor weight required is 100 x 800, which is 80,000 lb..