Ask the Silage Dr: Assessing Fresh-Cut Forage for Yeast

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Q.           How can I determine the level of molds and yeasts in fresh-cut forage before ensiling?

A.            It really all depends on local conditions, the crops, stage of maturity, stress events, damage events and the like.

Yeasts and molds are common on plants. They are saprophytes, meaning they live on and get nourishment from dead organisms or decaying organic material. Saprophytes recycle organic material in the soil, breaking it down into simpler compounds that can be taken up by other organisms/plants. When the plant is damaged (by frost, drought, wind, insects, etc.), the yeast and mold populations will increase.

If the plant is damaged by frost or drought, the whole plant is affected. So yeast and mold populations can exist all over the plant, although they will tend to be highest on and around the cob, which contains the most readily available (digestible) food source (sugars and/or starch, depending on maturity). If the plant is damaged by insects, the damage is likely to be more localized. Then the yeasts and molds will grow at these damage points and spread out radially.

In a healthy crop that has not been stressed or damaged, the yeast population could be up to a few thousand to a million colony-forming units (CFUs) per gram of forage, and the mold count could be up to a few hundred. The actual counts seen in a healthy crop will be more dependent on the stage of maturity, as populations increase as the plant ages. In a damaged stand, the populations of both could be high — peaking at around several hundred million to a few billion per gram, then declining as growth substrates are used up. Of course, while the numbers may be “stable” or “static” overall, the organisms are still growing or reproducing and consuming digestible nutrients to replenish those that die off, as the lifespan of molds or yeasts is quite short. Yeasts grow quickly on the readily available sugars and starches, followed by molds that produce enzymes that can break down complex plant materials (e.g., cellulose, “hemicellulose” fractions) into simple sugars for growth.

A population of yeasts and/or molds on the crop at harvest of anything over 100,000 CFU/g is a warning flag that there could be stability issues during feed-out. In these situations, I prescribe using an inoculant with Lactobacillus buchneri NCIMB 40788 at an effective dose level at harvest to help address stability challenges at feed-out. The high-dose-rate L. buchneri 40788 (400,000 CFU/g for silage, 600,000 CFU/g for HMC) has been reviewed by the FDA and allowed to claim efficacy in preventing the growth of yeasts and molds in silages and HMC. This helps delay, or even eliminate, heating and spoilage.

 

Thank you for this excellent question.

 

Sincerely,

The Silage Dr.

 

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