Chemical preservatives in animal feeds are used to extend shelf life and prevent spoilage by inhibiting microbial growth and slowing oxidation. Stored feeds can spoil due to molds, bacteria, yeast, and fat rancidity, especially in warm, humid conditions. Preservatives such as organic acids (like propionic, sorbic, and benzoic acids) and antioxidants help keep the feed stable, protecting its nutritional value and palatability over time. They aren’t intended to enhance flavor, raise crude protein, or neutralize toxins, which are not the roles of preservatives.

High energy concentrates are feedstuffs that provide calories; they are energy-dense ingredients like cereal grains and fats that supply a large amount of metabolizable energy per unit of feed and typically have low fiber. They are used to meet the animal’s energy needs without adding a lot of bulk. This is different from roughages, which are high in fiber and bulk but lower in energy density, and from mineral supplements or colorants, which do not contribute calories.

Fats are added to ruminant diets mainly to boost energy density. Fat provides more energy per unit weight than carbohydrate, so small amounts can meet high energy needs without requiring a large intake. This is especially useful during periods of intense energy demand, such as late gestation, peak lactation, or rapid growth, when an animal’s intake may not fully cover its energy requirements. However, unsaturated fats can upset rumen microbes and fermentation if fed in large amounts, reducing fiber digestion and potentially affecting milk fat synthesis. To get the benefits of fat without disturbing the rumen, producers use protected fats, which bypass the rumen and are digested in the small intestine. These protected fats deliver energy more predictably and are particularly valuable when animals face high energy demands but need to maintain rumen health or when the diet includes fatty acids that would otherwise disrupt rumen fermentation.

Roughages are low in energy mainly because they have a lot of structural material in their cell walls, i.e., high fiber content. The main components of plant cell walls—cellulose, hemicellulose, and especially lignin—are much less digestible than the nonstructural carbohydrates found in concentrates. Even in ruminants, where microbes can ferment some fiber, the energy yield per kilogram of dry matter from these fibers is substantially lower than from starches or sugars. The result is a lower energy density in roughages. Moisture level isn’t what drives the low energy; energy density is about what the dry matter actually provides. Low fiber would raise energy density, and high starch would also raise it, so those options don’t describe why roughages tend to be energy-poor.