Which Forage Is Finest? The Answer: It Depends.

By Christopher M. Peter, Ph.D., Dairy Technical Service and Research Scientist and Ricardo P. Arias, Ph.D., Manager of Dairy – Specialty Products & Technical Service at United Animal Health

In the last issue we discussed heterofermentative vs. homofermentative inoculants and the differences in bacterial species, fermentation end products, and efficiency of fermentation as it relates to the basic chemistry of reactions in the bunker. There are several other areas of interest as it relates to putting up and 'Feeding the Finest Forage.’ Some of these include the additions of acids and acid salts as well as enzyme additions to aid in the digestion of the fiber fractions of the forage.

Acids and acid salts directly lower the pH of the forage and inhibit the activity of microorganisms that do not grow at low pH and lead to spoilage (molds and yeasts). They can have advantages in poor weather conditions or where soil contamination is a problem. The newer generations are chemical-based additives containing mixtures of benzoate, nitrite, and/or potassium sorbate that have a similar mode of action to the traditional acids such as propionic, but they are non-corrosive and when applied at the recommended rates do not negatively affect the fermentation process.

Enzymes are proteins involved in metabolic processes. The use of cellullases and hemicellulases aid in digesting the cell wall of forages, making the sugars more readily available for the bacteria in inoculants, and thus reducing pH faster and reducing dry matter losses. In addition, partial digestion of the cell wall also improves digestibility of the feed. Enzymes also produce metabolites that the bacteria can use as a food source early in the fermentation process.

What works best?

Like almost everything else in our business, it depends. First, make sure the product you are using has enough bacteria in it. Research shows that you need a minimum of 100,000 cfu (colony-forming units) in homofermentative products to overwhelm natural bacteria in optimal conditions. For heterofermentative products, a minimum of 400,000 cfu is required due to their slow growth rate. Second, use liquid-application inoculants whenever possible. There are a few reasons why we prefer water-soluble inoculants:

Lastly, the type of inoculant you use depends on the forage and what you want to accomplish with it. In most cases, a combination of homofermenters and a mold-inhibiting acid will provide optimal fermentation and excellent dry matter recovery. While also directly or indirectly delivering an acid that will give the good bacteria a headstart and improve aerobic stability.

A homofermentative inoculant + a mold-inhibiting acid is a good choice for legume silages. Legumes, like alfalfa, have less water-soluble carbohydrates than grasses or corn making it more difficult to create a fast decline in pH and making them more susceptible to clostridial fermentation when ensiled too wet (> 65% moisture). Therefore, an inoculant that will efficiently produce lactic acid from the available sugars is our recommendation.  

A heterofermentative-only inoculant is a good choice for crops and farms where spoilage has been an issue in the past and/or for silage piles destined to be used in the hotter months of the year. The increased acetic acid produced by these bugs help increase aerobic stability by slowing down the growth of molds and yeasts that cause heating and spoilage. So, if you are willing to sacrifice nutritional value for increased aerobic stability at the bunk, this may be a good option for you.

A combination product with 3 or more strains + a mold inhibitor and enzymes is what we recommend on most of the operations we serve. The latest research from the USDA Forage Research Center shows a 3.5% increase in animal performance with homofermentative silage inoculants. The same results were not observed with the heterofermentative products that use L. buchneri.

 It is important to understand that inoculants are not silver bullets. Poor silage management causes many of the spoilage issues we find in the field; ensiling overly dry or wet crops, poorly packed and sealed bunkes/piles, and low feed out rate are issues that should be addressed to improve the success rate of the inoculants being used. Nevertheless, a good inoculant program in concert with the aforementioned management practices can help ensure you Feed the Finest Forage.  For more information please visit UnitedAnH.com/Forage.

To read the first article in this Silage series, please click here.