Justified concern for wet silages
|By Michaela King|
It’s been a wet growing season — one of the wettest in recent memory — and harvest conditions have been less than ideal. Some first crop alfalfa and small grain silages that have been harvested or are starting to come off the fields may be wetter than desired.
In a recent Vita Plus Forage Foundations article, Michelle Der Bedrosian, a Vita Plus forage products and dairy technical specialist, warns that wet silages are at risk for the growth of harmful bacteria during storage. “The presence of ‘bad bacteria’ in silos is inevitable, but their growth is not,” she says.
Clostridia, bacteria often found in wet silage, thrive in high-moisture environments, and their activity and growth lead to health issues in cattle such as hemorrhagic bowel syndrome and salmonellosis. Growth of the bad bacteria also degrades the quality of the silage.
“Their activity results in high dry matter (DM) losses and poor-quality silage, and they can also degrade sugars into butyric acid and valuable proteins into biogenic amines and ammonia,” Der Bedrosian says.
The most important factor in preventing clostridia bacteria growth and butyric acid formation is to ensure that the crop is ensiled at the right dry matter. Silage that is too wet will be susceptible to clostridia growth, but silage ensiled too dry will be difficult to pack.
Der Bedrosian and Pat Hoffman, a retired University of Wisconsin dairy specialist and current dairy technical specialist for Vita Plus, suggest chopping small grain silage at half an inch and ensiling at 33 to 36 percent DM. Ensile alfalfa at an even lower moisture level with 45 to 55 percent DM.
Already in the silo
The best way to deal with bacteria growth is to prevent it; however, sometimes silages are ensiled too wet and high levels of butyric acid are formed. When this happens, there are some options to prevent wasted silage and health issues in cattle.
Der Bedrosian notes, “Clostridia take two to three months to grow, and if you can feed the silage before the bacteria have a chance to grow, you can get more milk per acre from that same feed.” She advises to have suspect silage tested before feeding to ensure it is safe. Many labs can do a profile test for volatile fatty acid (VFA) concentrations.
Once butyric acid concentrations are higher than 0.5 percent DM, avoid feeding the silage to transition cows. Heifers and late-lactation cows can better tolerate silages that are high in butyric acid.
The specialists also recommend lowering the butyric content by airing out the silage. “Because butyric acid is volatile, and these silages are very stable, laying out the feed in a thin layer prior to feeding can volatilize a lot of the butyric acid,” they say.
Der Bedrosian and Hoffman conclude that the best way to prevent bacteria growth is good management practices, which are not always easy to achieve. “Unfortunately, at times, dairy farming seems to be more of an art than a science, but at the end of the day, we have to feed what we have available,” they note.