The Silage Bacteria Battle

Mike Rankin
Crops and Soils Agent - Fond du Lac County
University of Wisconsin - Extension

Over the years, I’ve written several articles about silage inoculants and had countless discussions with producers and company folks regarding their use.  Offering a “can’t miss” recommendation has been about as easy as nailing Jello to a tree.  There’s still a lot to learn about silage inoculants but I’m currently more positive about their use than was the case ten years ago.

This change in attitude has been brought about by several factors.  First, there’s a lot more research on these products.  In a summary of all inoculant research trials reviewed by Dr. Richard Muck of the USDA Dairy Forage Research Center, fermentation of silage was significantly improved for alfalfa in nearly 75% of all trials.  Positive fermentation results were noted 71% of the time for grass silages and 40% for corn silage trials.  In studies where positive responses for milk production were measured, Muck indicates this has occurred about 40 to 50 percent of the time across all studies.

In addition to a stronger silage inoculant research base, some inoculant companies have put considerable resources into developing and selecting strains of bacteria that are more effective than was the case ten to twenty years ago.  Many of the bacteria strains used today are crop specific rather than “one size fits all”.

The good guys vs. the bad guys

Many factors influence silage fermentation.  According to Dr. Limin Kung, respected inoculant researcher at the University of Delaware, the more important ones include the types and numbers of naturally occurring microorganisms, the amount of soluble (fermentable) sugars, the rapid elimination of oxygen, the silage moisture content, and the buffering capacity of the crop.

As the crop is ensiled, the war begins between the good bacteria and bad bacteria.  The good guys are the lactic acid producers (LAB).  The bad guys include enterobacteria that compete with LAB for sugars and can produce detrimental endotoxins.  Eliminating oxygen and acidification will help keep these guys on the bench.  The bad guys’ team also includes yeasts and molds that also do quite well in the presence of oxygen.  Yeasts compete for fermentable sugars and are primarily responsible for the aerobic spoilage of silage.  Molds, as many producers have learned first-hand, produce mycotoxins that have negative effects on animal performance and health.  Clostridia are organisms that thrive under moist conditions and degrade sugars and proteins.  They can be controlled by wilting forage above 30% dry matter.  Dr. Kung points out that when any of these bad guys control the tempo of the silage game, fermentation pathways are extremely inefficient and large losses in dry matter can occur.  For example, where clostridia (wet silage) or yeast (dry silage) predominate, dry matter recovery is reported at only 50 percent.

Love those LAB

The fundamental reason to invest in silage inoculants is to insure there are enough LAB for optimum silage preservation.  This is not to say there may not be sufficient numbers already on the wilted crop.  Factors that promote the growth of naturally occurring LAB to sufficient levels on alfalfa include long wilting periods (>2 to 3 days), low silage moistures (<60%), and high average wilting air temperatures.  Based on this, we would expect our greatest economic return from using alfalfa silage inoculants on first and fall cuttings (low average wilting temperatures), fast dry-down summer harvest conditions (<1 day wilting period), and where silage is harvested for bunker silos at higher moistures (65 – 70%).

General thoughts and recommendations..

Okay, let’s boil this inoculant issue down to some practical advice.  Here it is………….
 

• Based on current research and inoculant price, using inoculants “across the board” on all alfalfa and corn silage ensiled will likely result in a worst case scenario of  “breakeven” but likely will be better.  Returns could be highest by limiting applications to situations and crops where naturally occurring LAB are not already present in the crop at sufficient levels.

• The likelihood of positive fermentation and production benefits is highest with alfalfa and grass silage and somewhat lower with corn silage.

• When using inoculants, apply at a minimum rate of 90 billion live lactic acid bacteria per ton of crop.  Store inoculants in a cool, dry environment to maintain viability.  I know of no positive research results from inoculating silage with dead bacteria.

• If possible, purchase inoculants that are labeled for the crop you are ensiling and from a reputable company with a history of inoculant testing and research.  Read the product label and look at the types of bacteria being applied.  They should include one or more Lactobacillus species.
  
  
• LAB do not “swim” around the silo.  Inoculants must to be applied uniformly to the crop.  This is best accomplished when applied in a liquid form at the chopper.

• Lastly, and perhaps most importantly, silage inoculants will not cover-up for otherwise poor silage harvest and storage management.

For more information contact Mike Rankin