Pack, pack and pack, says Andy Skidmore, DVM, PhD, a technical services specialist with Lallemand. Skidmore discussed a range of impacts and management factors influencing silage spoilage at a recent Academy of Veterinarians conference, stressing the importance of sufficient packing in the bunker, encouraging proper pH levels in the pile and protecting silage quality through feeding.
With proper harvest, packing and storage, desirable microbes quickly ferment the silage, producing lactic acid which lowers the pH level to protect the feed from contamination with undesirable microbes associated with spoilage and toxicity to cattle. Fermentation also produces acetic acid, which helps control undesirable growth of yeasts and molds upon exposure to air at feedout, when silage quality can decline quickly.
In addition to yeasts and molds that cause spoilage and reductions in nutritional value of silage, contaminants can include pathogens such as salmonella, listeria, clostridia and mold-associated mycotoxins, Skidmore says.
Sources of contamination in silage can include:
· Soil, which increases buffering capacity in the silage.
· Plant damage from insects, hail or flooding.
· Manure or lagoon water used on fields.
· Decaying carcasses of rodents or other animals caught by the silage harvester.
· Molds and resulting mycotoxins in the crop fields.
· Wild yeasts, which can negatively affect aerobic stability of the silage, or the time the silage remains cool upon exposure to air.
Pathogens such as salmonella and listeria and botulism can grow in silage when the silage pH level does not drop quickly enough after harvest, and subsequently cause health problems in cattle.
Surface spoilage in silage produces heat, water and CO2 as spoilage byproducts, while reducing dry-matter content, palatability and nutritional value of the feed. Skidmore offers an example of a 250- by 400-foot bunker silo, with 21 inches of shrink due to surface spoilage. That shrink adds up to 3,937 tons of lost feed. At a value of $45 per ton, the financial loss to the producer is $177,185.
The pH of good-quality silage typically runs around 3.8, Skidmore says, while the pH of spoiled silage can jump as high as 8. Dry matter content in normal silage averages around 37%, compared with 18% dry matter on the surface of spoiled silage.
Skidmore described a trial in which researchers fed cattle a ration of 90% silage, at various levels of spoilage, and 10% supplement. They included spoiled silage at 0%, 25%, 50% and 75 percent of the silage component. They observed a linear decline in dry-matter intake and neutral detergent fiber (NDF) digestibility as the ratio of spoiled to normal silage increased, with an especially large drop as the percentage of spoiled silage increased from 0 to 25 percent.
Even at 5% of a ration, Skidmore says spoiled silage reduces NDF by about 7%.
Regardless of how well a bunker is packed and sealed, eventually the silage becomes exposed to air as it is removed and fed. Air exposure “wakes up” yeast cells in the silage, and as the yeast reproduces, it degrades residual sugars and lactic acid in the silage. This process destroys nutrients, creates heat and increases the pH in the silage. The higher pH allows growth of molds and bacteria that contribute to more spoilage and, potentially, production of toxins. Skidmore says though, that most toxins found in silage come the field, rather than developing in the bunker.
Upon exposure to air, the number of yeast cells in the silage can double every two hours. Normal silage has around 40,000 yeast cells per gram, Skidmore says. Within 10 hours, that population can grow to 1,280,000 cells per gram, and within 16 hours the population per gram can exceed 10 million cells. Problems with yeast-related heating and spoilage tend to begin at around 1 million cells per gram, so silage removed from the bunker and left overnight before feeding probably has begun to decline in quality.
Proper “facing” of the silage pile as feed is removed should leave a smooth, uniform, vertical wall of packed silage to minimize surface area and air exposure. On an improperly faced pile, Skidmore says, air can penetrate up to three feet, meaning the operation is virtually always feeding heated silage.
The process begins with good-quality forage going into the bunker, meaning harvesting the crop at the optimal maturity and moisture content, chopping to the right length and processing the crop appropriately. Skidmore says that for corn silage, the “milk line” is not necessarily the best indicator of maturity in today’s corn hybrids, so talk with your seed dealer about the best time to cut a particular hybrid for silage.
Using a silage inoculant helps with rapid initiation of fermentation and reduction in pH in silage, reducing spoilage during storage and at feedout. Use proven inoculants from reputable companies and follow instructions for best results. Skidmore says, for example, he sometimes sees operators place the inoculant container right next to the harvester’s engine compartment, resulting in heating and destruction of the active microbes in the inoculant.
Once the crop is thoroughly packed in the bunker, cover and seal it well with plastic and sufficient weights, such as used tires, to hold the plastic in place. As silage is removed from the face, keep the cover in place right up to the face, rather than uncovering several days’ worth of the bunker’s surface at once.
Silage contamination leads to poor cattle performance, Skidmore says, adding that in silage management, a pound of prevention truly is worth 100 pounds of cure.