How Inoculants Lower pH and Preserve Nutrients
By Bill Powel-Smith
Producers want to know the inoculant products they buy are working. Bunker evaluations using compost thermometers, infrared cameras and density probes have become the unbiased voices producers have been looking for. These tools help piece together the story of fermentation and stability of forages.
We can now demonstrate the role inoculants play in providing year-round, high-quality, fermented forage to the cow. Inoculant choice is part of a group of key decisions producers make when putting up forage. Success depends on inoculant selection combined with plant harvest moisture, chop length, packing and covering.
Porosity and Density Influence Fermentation
Two factors that impact fermentation are silage porosity and density. Porosity influences air's ability to move through the silage mass and penetrate deeply. Forage that is drier, coarsely chopped or not packed densely enough is more porous. Density refers to how much feed an operator can pack into a cubic foot of silo, bag or bunker. Fine chopping or shredding and extra heavy equipment help increase density. Producers should limit porosity and ensure adequate density.
Inoculants Lower pH Quickly
Fresh forage has just a few hours before it can start to heat, lose nutritional quality, and begin to decompose. But fermentation, the lowering of pH to a stable point of 4.5 in haylage and 4.0 in silage, aided by inoculants can help produce fermented feed with a shelf life lasting many years.
Bacterial inoculants initially feed on sugars and produce acids, particularly lactic acid, to lower the pH. Inoculants work because these lactic acid bacteria quickly multiply in the forage mass. While forages naturally contain some lactic acid bacteria, unaided fermentation can take a long time. A longer fermentation period produces more heat, consumes more sugars and starches, and breaks down valuable protein into ammonia.
Inoculants that contain lactic acid bacteria-such as L. plantarum, L. casei, Enterococcus faecium and Pediococcus species-will increase the rate of fermentation during the initial process, helping reach terminal pH as soon as possible.
Fermentation failures occur in areas when too much oxygen is available and the process of lowering the pH slows or stops. This happens because the aerobic (oxygen-loving) bacteria can grow unchecked and dominate the lactic acid bacteria. Higher porosity areas, often near the outer rim of structures, will show mold or spoilage.
If water enters the silage and dilutes the acids, layers or areas of spoiled feed may appear. This happens if rain falls on forages during filling, when feed is overpacked (cell walls rupture and excess plant moisture accumulates into a layer) or when holes in the covering allow water to leak in.
When fermented feed is re-exposed to oxygen during facing and feedout, dormant yeasts become active and feed on the lactic acid, raising silage pH and allowing the "decomposition microorganisms" including molds to begin breaking down the feed (akin to composting). Heat probes allow us to measure the heating that occurs during this decomposition.
The Power of Lactobacillus buchneri
Inoculants with high-quality L. buchneri bacteria can minimize the need for total mixed ration (TMR) heating stabilizers, even during hot days.
Superior inoculants delay heating for an extended time, allowing producers to feed cool feed. Other inoculants allow feed to heat and spoil within hours, a process operations can easily monitor. Even tightly packed bunkers can allow air to penetrate 2 or 3 feet into the face. For example, if a farm is feeding 6 inches a day and air is seeping 36 inches into the pile, the feed may have been exposed to air for six days before the cows take their first bite. A high-quality L. buchneri inoculant can keep feed cool and fresh for cows for the next day or two.
An ideal inoculant will combine lactic acid bacteria strains that improve the rate of fermentation on the front end with different lactic acid bacteria strains that reduce heating during feedout. Superior inoculants will contain multiple strains of lactic acid bacteria specific to address both needs.