Density And Losses In Pressed Bag Silos

Silo bags offer producers a flexible way to store feedstuffs. They can be used for a wide array of feeds, including forages, high moisture grains, and by-products. The filling method is simple: forage is pressed through a rotor into the silo bag by a filling machine.

This storage system is popular with many producers because it offers an excellent alternative to upright and bunker silos. The main benefits of silo bags are that they are economical, offer versatility and enable the producer to easily keep inventory. Since bags are available in a range of diameters, they can be utilized on operations of any size.

In all storage systems, dry matter loss is directly correlated to packing density. The lower the bag’s packing density, the greater the dry matter losses. This reality prompted Drs. Brian Holmes and Richard Muck from the University of Wisconsin to look at dry matter density in different areas in silo bags. Their research resulted in some interesting findings, which are detailed here.

Researchers from the University of Wisconsin monitored three locations in 25 silo bags. The bags were filled by different machines and with different forages.

Results Regarding Density

•   Drier silage resulted in higher porosity. Porous forages allow more air penetration into the silage bag. Exposing the silage to air and oxygen can initiate spoilage and increase dry matter loss.

•   Density also decreased as particle size increased.

•   Method of operating the bagging machine impacts the silage density.

The average density at the three locations varied between 11.5 and 17 lbs of dry matter/foot. Interestingly, there is a wide range in densities, but overall the density is similar to, or maybe a little lower than, what is commonly found in bunker silos.

Figure 1 shows the differences in densities across the face of a silo bag. When researchers “equated” the density of the center bottom region to be 100%, they found that the density at the top center of the bag was only 37%. Air will penetrate these less dense areas of the silo bags faster. Therefore, it is crucial to feed out at high enough rates to keep up with the air penetration and subsequent spoilage.

Trends The Researchers Observed

•   Seepage losses occurred when crop moisture exceeded 68%.

•   Bird damage to the top of the bag can cause a 22% dry matter loss.

•   Highest losses were found when silage was either too dry or too wet.

•   Over half the bags had little or no spoilage.

Conclusions/Recommendations

Management has a big impact on the level of dry matter loss.

•   Moisture, length of chop and correct filler operation are especially important factors.

•   Holes and damage to silo bags must be patched to prevent forage spoilage.

•   Feed-out at least 2 feet per day to account for the low density in the top of the bag.

Overall, silo bags can be a great addition to a feeding program, especially for expanding dairies looking for flexibility and lower capital cost.

Vigortone has two silage inoculants that are crop specific. Vigorsile® III is a bacterial inoculant for use on alfalfa haylage, small grain silages, and grass silage. It is specifically designed to ferment crops that have a high buffering capacity and low level of carbohydrates. Vigorsile EBL II is specially designed for corn and sorghum silages and high moisture grains. In addition to bacteria that produce lactic acid, EBL II also produces active yeast and mold inhibitors. Each Vigorsile product comes in package sizes to fit your operation.

This article was published in the June 2004 edition of Vigortone's Bunk, Bull & Business newsletter.