Fermentation byproduct load is not an official feed-label term. It is a practical way of describing the extra compounds left behind or concentrated after a fermented ingredient is processed.
With maize distillers dried grains with solubles, or corn DDGS, the corn starch is fermented to make ethanol. After the starch is removed, the remaining material is dried and used in feed. That leftover material can be nutritionally useful, but it is also more concentrated than plain corn in certain things.
In practical terms, the “fermentation byproduct load” may include:
Residual yeast and fermentation residues
Concentrated protein and fiber fractions
Higher phosphorus
Possible higher sulfur
Concentrated corn oils, often higher in omega-6 fats
Solubles, which are the liquid fermentation residues added back before drying
Heat-processing residues, depending on drying temperature
Potential concentration of mold/mycotoxin issues if the original grain quality was poor
It does not automatically mean the ingredient is bad. In many feeds, DDGS is used because it adds protein, calories, fat, phosphorus, and palatability. But in a sensitive horse, metabolic horse, ulcer-prone horse, allergy-type horse, or horse with inflammatory symptoms, I would look at it as an ingredient that can add more processing complexity than simpler ingredients like beet pulp, alfalfa meal, flax, or a clean ration balancer.
So when I say fermentation byproduct load, I mean:
The combined nutritional and processing residues that come along with a fermented grain co-product, beyond just simple protein, fat, and fiber.