**5. Improving adoption of forage inoculant use by increasing awareness of the economic value of forage inoculants**

According to the 2017 National Agricultural Statistics Survey [44] census report, approximately 120,000,000 tons of whole-plant corn alone was harvested for silage in the United States. Even with this huge quantity of silage, there is little reliable survey data about the use of forage inoculants.

Based on an independent market survey of U.S. beef and dairy producers, two thirds of respondents indicated that forage additives used on their operations are microbial based. The main reason for their use is to minimize mold and spoilage in silage. Other reasons cited include preventing heat damage and increasing herd productivity [45]. Most inoculant users plan on continuous using and investing in this technology each year (personal communication).

Product performance, ease of use, and cost are the main influencers on the purchasing decision of inoculants. In addition, nutritionists and consultants are important sources for providing information on forage inoculants and the most involved outside sources in the purchase decision (personal communication).

Most producers do not have a detailed understanding of the different types of inoculant products, but they instead recognize the value and return on investment (ROI) that these technologies can bring to their operation. Value-added services and education offered by inoculant companies are also reasons to purchase, especially for larger producers.

*New Advances on Fermentation Processes*

silage [25].

**4. Improving aerobic stability using forage inoculants**

fermented by spoilage microorganisms in the presence of oxygen.

system [30], like *Lactobacillus reuteri* [28].

several metabolic pathways in yeast cells [31].

Silage feedout is the final phase of the ensiling process. At that moment, oxygen

The process of aerobic deterioration of silage involves a shift to aerobic metabo-

Following the isolation of a *L. buchneri* strain [26], researchers described its unique metabolic pathway, which consisted of converting moderate amounts of lactate under low pH to equal parts of acetate and 1,2-propanediol [27]. The latter chemical is an intermediate in the potential synthesis of propionic acid. *L. buchneri* does not have the gene to complete the reaction, so another species of LAB has to be involved to convert 1,2-propanediol to an equimolar amount of 1-propanol and propionic acid [28]. This conversion was initially observed in silage by *Lactobacillus diolivorans* [29], but other members of the buchneri group also possess the genetic

Compared to lactic acid, the key feature of acetic and propionic acids in improving aerobic stability of silage is based on the difference in p*K*a between these weak acids and lactic acid, which is a stronger acid, with a p*K*a of 3.86. At higher p*K*a, 4.76 for acetic acid and 4.86 for propionic acid, these weak organic acids will have a low dissociation level under most ensiling conditions, thus allowing for passive diffusion inside the yeast or other microorganism cytoplasm. Once inside the cytoplasm, propionic acid will dissociate to the corresponding salt since internal pH is above p*K*a value. The same process is also possible for acetic acid. Constant pumping of the protons released inside the cytoplasm causes physiological stresses impacting

Length of fermentation and establishment of heterofermentative LAB population are now considered critical toward the establishment of a good aerobic stability level. The facultative, or obligate heterofermentative, strains of LAB have lower growth rates than homofermentative strains, including rods like *L. plantarum* or coccids of the genera *Leuconostoc*, *Enterococcus*, or *Lactococcus*. The growth conditions after several days of ensiling are also more restrictive for physiological activities considering the low pH usually encountered. The strains succeeding the earlier colonizer need to be more tolerant to both acidity and osmotic stresses, simultaneously. Observation of the succession of different species of LAB during the anaerobic stability phase often leads to high abundance of LAB belonging to the *L. buchneri* taxonomical group [32], leading to specific adaptation to this ecological niche by these strains. Although few physiological studies on *L. buchneri* strains had been published, Heinl and Grabherr recently published a complete analysis of the genetic potential of the strain CD034 compared to other genomes from public databases [33]. One of the comparisons performed aimed to describe how the genetic system of this species can cope with high concentration of organic acids, including lactic acid. The anaerobic conversion system of lactic acid to 1,2-propanediol

can slowly diffuse inside the silage mass. Diffusion speed will be influenced by different factors, including the level of humidity, porosity, and temperature of the

lism in some microorganisms and the reactivation of strict aerobes that were dormant. Reduce nutritional value due to oxidation of the fermentation products, of carbohydrates, amino acids, and lipids to H2O, CO2, and heat. Simultaneously, the higher metabolic activity will increase the silage temperature, accelerating microbial growth. Several microorganisms are involved, but yeast and acetic acid bacteria are adapted to tolerate the initially low pH conditions and thus able to exploit this niche before pH increases following the catabolism of the organic acids. Crops with higher levels of easily accessible carbohydrates are more prone to aerobic deterioration, i.e., corn, sorghum, and sugarcane, since these sugars can be readily

**160**

Producers may often choose not to purchase forage inoculants due to the cost of the products. Other top reasons that influence purchase decisions are (1) not believing inoculants work, (2) lack of knowledge, or (3) lack of specific equipment for inoculating the forage. With all these factors in mind, there is a strong need for proper education on the application and showing the cost-to-benefit calculation of these forage additives (personal communication).

Even though some producers are nonusers, they believe that inoculants have the potential to improve consistency of silage quality, enhance ration quality, and increase feedout stability. In the same question, just 40% answered that improving ROI is one of the most important benefits of purchasing inoculants. Even though some producers do not associate inoculants with contributing to overall herd ROI and profitability, they positively associate the word "fresh" to silage having a good smell and high palatability (personal communication).

During typical field and harvest management conditions, silage losses are easily reported between 15 and 20%. If inoculant use can reduce DM losses by 5 percentile points, there would be savings of \$2000 (US\$) per thousand tons of silage, assuming the silage is valued at \$40.00 (US\$) per ton FM. Moreover, silage with high degree of deterioration not only has less overall tonnage to be fed, but the feed is also of lower nutritional quality.
