Opening a silage bunker this year might be analogous to Forest Gump’s box of chocolates; “you never know what you’re gonna get.” With the challenges of the 2019 growing and harvest season in the Midwest and Northeast, a lot of forage was put up under less than ideal conditions.
Two big concerns are:
1. Many fields had standing water. This increased the likelihood of soil and/or manure contamination.
2. Dairy farmers were forced to chop forage between narrow windows of frequent rains last fall, regardless of ideal plant moisture.
Soil contamination and wet silage may result in compromised fermentation.
Pay attention to total ash content. This will give you an indication of soil or dust contamination.
Typical Total Ash Content of Forages (Uncontaminated)
Corn Silage 3.5 - 4.0%
Grass, sorghum, small grain silages 6 – 8%
Alfalfa haylage 9-10%
If neutral detergent fiber (NDF) as a percent of dry matter is more than 2% higher than NDF as a percent of organic matter (NDFom), then expect soil contamination. However, since manure is mainly organic matter, this metric won’t account for additional manure contamination.
Soil and manure contamination can contribute some really bad bacteria, like clostridia and enterobacteria. Not only do these bugs raise havoc with the fermentation and palatability of silage, they produce toxins that can destroy the GI tract of a cow.
Clostrium perfringens is a particularly bad actor. We have seen very high levels of C. perfringens in Florida as a result of grass fed fresh as green chop. We determined the cause as soil contamination due to the vacuuming effect of the choppers. This has caused particularly severe digestive issues, including hemorrhagic bowel. Enterobacteria, also from soil contamination, include E. coli, Salmonella and Klebsiella. Biogenic amines are produced by both clostridia and enterobacteria. These compounds have a negative effect on rumen function.
Silage pH below 5.0 will minimize clostridial growth. Ensiling with a good homolactic lactic acid bacteria inoculant to rapidly reduce pH will minimize potential problems. Cold temperatures will deter growth of these pathogens, so some of these issues may not rear their ugly heads until spring.
If you do suspect a problem, a proven direct fed microbial (DFM) or live active dry yeast product can reduce the potential effects of these toxins. Look for layers imbedded within the face of the silage that may appear wet or may have a different coloration. Even a small percentage of bad silage may affect cow performance and health. You may need to reduce the inclusion of contaminated silage in the TMR.
The major dairy labs, as well as DFM suppliers, can test your silage for the presence of clostridia by an NIR fermentation profile. Any butyric acid present will likely have been produced by unwanted clostridial activity. This will be accompanied by high ammonia levels (greater than 15% of crude protein).
Enterobacteria can be detected by the signature of VFA they leave behind, according to Tony Hall of Lallemand Animal Nutrition. A comprehensive wet chemistry fermentation analysis may be needed, as NIR does not provide a wide range of some of the end products produced. These end products include 2,3 butanediol and a mix of other alcohols (ethanol, propanol, butanol, methanol) plus succinic acid. High yeast counts, ammonia, butyric acid and acetic acid are indicators of poor fermentation. Guidelines for thresholds are available on the major dairy lab web sites.