The mystery and magic of silage inoculants

By Mike Rankin

One of the most often discussed, misunderstood and argued topics in the forage production feed chain is the use of silage inoculants. There are top-managed farms that don’t use them and many that do. This has been the case for a lot of years, but lately the inoculant discussions have been elevated along with the science.

While at a recent media event offered by DuPont Pioneer, Bill Rutherford, a senior research manager with the company, said, “There are strains of bacteria on this earth that can do about anything you want. We just have to find them.”

Of course, it's a bit more complicated than that, but the point is well taken and job security in the silage inoculant research sector seems pretty solid given the millions of potential bacteria strains to be screened and tested. Fact is, even a bacteria that appears beneficial for whatever reason has to be able to compete with its brethren bacteria in the hostile environment we call fermentation.

At the core of the discussions — and sometimes arguments — regarding silage inoculants is that bacteria are fickle little beasts when it comes to their work environment. Temperature, moisture, crop species and who knows what else impact the way they like to play and the final results of their activity. This is why it is not difficult to find research that will prove or disprove whatever point you wish to make. Welcome to life in the biological sciences.

For the past 30-plus years, lactic acid-producing bacteria have been the most commonly marketed silage inoculants. We know they usually accelerate the fermentation process and reduce dry matter loss. Usually, however, is not the same as always. Even so, there have been instances where fermentation wasn't changed by inoculants when compared to untreated silage but animal performance (milk production, weight gain, feed efficiency) was improved. But how?

Some of the current thinking is that the inoculated silage is impacting microbial biomass (number or type of bacteria) and/or bacterial activity in the rumen of the animal such that digestibility or nutrient utilization is improved. Researchers continue their quest to further explain this response (with or without silage fermentation improvement).

One of the biggest gains in silage inoculant research has been the introduction of Lactobacillus buchneri to improve aerobic stability. Unlike the homolactic acid compounds that occasionally make aerobic stability worse, L. buchneri consistently improves the stability of silage and is especially beneficial for corn silage and high-moisture corn. Many companies now market combination products containing lactic acid-producing bacteria and L. buchneri, which produce some lactic acid along with several anti-fungal products including acetic acid. DuPont Pioneer recently announced at its media event that their new generation L. buchneri products provide aerobic stability in seven days, a significant improvement over the initial strains that often took 50 to 75 days postensiling.

Silage inoculant research continues to roll on with an emphasis on using bacteria to improve feed quality in the silo and/or enhance utilization of feed in the rumen. It’s long been said that silage inoculants won't turn bad silage into good silage, but they will make good silage even better. There is still management involved. Over the long haul, it makes economic sense to use silage inoculants with the realization that environment and year-to-year variation will result in a range of responses. You’ll improve your odds of return with research-backed products and by using bacterial strains that are crop specific.

In my former life as an extension agent, I was once asked to evaluate several inoculant products for the state-run dairy farm. I was given the bacteria portfolio (type and number) for each product along with the recommended application rate. Company names were withheld. I was shocked at the differences between the products and the respective company recommendations for use. Moral of the story: It’s a buyer beware world when it comes to silage inoculants. Do your homework.

In the silage world of big farms, big machines and big silos, it might be the magic of microscopic bacteria that eventually redefine silage as a feed source. Before that happens, however, there are still a lot of mysteries to unravel.