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Do Silage Inoculants Offer Up a Return on Investment?

Taylor Leach


April 5, 2021



At the base of any good dairy cow feed ration typically lies ensiled forages. They’re relatively easy to grow, can store for long periods of time and offer up the nutrients necessary to support milk production. However, if these forages are not properly preserved, they can easily spoil, causing palatability to plummet and your feed bill to skyrocket.


When forages are correctly ensiled, water-soluble carbohydrates are converted into organic acids by bacteria naturally found on the leaves of plants, according to Donna Amaral-Philips, a dairy Extension agent for the University of Kentucky. These organic acids, mostly lactic acid, lower the pH of the ensiled crop, thus preserving the forage crop and inhibiting the growth of spoilage and pathogenic bacteria. However, once the silage is exposed to oxygen, yeast and mold can grow, speeding up deterioration.


To help keep silage preserved, two different types of silage inoculants have been developed over the years — lactic acid bacterial inoculants and inoculants to extend bunk life. However, these additives can come with a hefty price tag. This poses the question: Are silage inoculants worth the money? The answer? It depends.

Lactic Acid Bacterial Inoculants


“Inoculants containing lactic acid bacteria (LAB), such as Lactobacillus plantarum, include some of the older types of bacterial silage inoculants,” Amaral-Philips notes. “These inoculants were developed to cause a quicker drop in the pH of silage crops shortly after ensiling, as well as decrease the pH of the crop during the entire fermentation process.

This drop in pH inhibits the growth of undesirable microbes, such as molds or clostridia and prevents the loss of nutrients in the ensiled crop.”


The effect LAB inoculants have on ensiled forages vary by crop. For example, in alfalfa and grass silages, silage inoculants decrease the final pH of silages, increase lactic acid concentration, increase dry-matter recovery and decrease mold counts, thus improving overall silage fermentation, according to Amaral-Philips. However, these responses were not seen as frequently in corn or sorghum silages, possibly because harvested corn or sorghum plants already contain sufficient water-soluble carbohydrates to support adequate lactic acid synthesis.


“Forages treated with this type of inoculant generally have lower acetic acid content and, consequently, contain higher yeast counts,” Amaral-Philips says. “Acetic acid acts as an anti-fungal agent and higher lactic acid concentrations act as a growth substrate for spoilage yeasts. These changes decrease the stability of silages at time of feedout resulting in heating at the feedbunk or open face of the silo.”


Though the responsiveness of ensiled forages to LAB inoculants varies, one small but positive contribution is the slight increase in daily milk production along with a small boost in dry-matter intake and increased fat and protein percentages. According to Amaral-Philips, scientists speculate this might be related to an inhibition of detrimental molds and toxins and changes in rumen fermentation.

Inoculants to Extend Bunk Life


In comparison to LAB inoculants, inoculants crafted to extend the bunk life of ensiled forages typically contain heterofermentative bacteria, which improve the stability of silages at feedout and on the face of an opened silo.


“This type of bacteria converts lactic acid found in the silage to acetic acid, lowering yeast counts, resulting in less heating of silage in the feedbunk and on the exposed face of silos,” Amaral-Philips says. “These increases in acetic acid content take 30 to 60 days post ensiling before they are detected.”


Research has shown untreated silage increased in temperature by 2°F to 3.5°F within 25 hours versus 503 hours for silage treated with Lb. buchneri at application rates greater than 100,000 cfu/g.


“This longer stability is more important in helping maintain the quality of silage found just interior to the exposed face of silos,” Amaral-Philips says. “Removing silage from the face allows oxygen to enter the stored pile just interior to the exposed face. The depth of this oxygen infiltration is dependent on how deep from the face packed silage is disturbed when removing silage for feeding.”

Combination Inoculants


To preserve silage for a longer period of time, a combination approach of inoculants work best.


“Commercial products are available that combine both types of inoculants,” Amaral-Philips says. “The LAB bacteria would help control the early fermentation process resulting in a more rapid drop in pH, suppressing undesirable microbes, reducing the breakdown of proteins, and decreasing losses of dry matter especially in grass and alfalfa silages. The Lb. buchneri bacteria would improve the stability of the ensiled forage at feedout and at the open face of the silo.”

Shoot for Silage Success


“Success when using a silage inoculant starts and is dependent on one practicing sound silage preservation management practices,” Amaral-Philips says. “Preserving quality silages starts with harvesting the crop at the proper stage of maturity and moisture, adequately packing to exclude as much oxygen as possible, and covering the silage to prevent water and oxygen infiltration.”


Before selecting a silage inoculant product, Amaral-Philips suggests doing your homework and requesting research showing the product works as advertised.


“With corn and sorghum silages, the effects with the use of LAB bacterial inoculants are less definitive as they relate to changes in the fermentation process,” she says. “Use of these products may act as an insurance policy for times when conditions are not optimal for a successful fermentation. The question becomes, is that cost justified? The use of Lb. buchneri extends the stability of silages at feedout irrespective of crop.”


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