Phytogenic feed additives (often also called phytobiotics
or botanicals) are commonly defined as plant-derived
compounds incorporated into diets to improve the
productivity of livestock through amelioration of feed properties, promotion of the animals’ production performance,
and improving the quality of food derived from
those animals. Although this definition is driven by
the purpose of use, other terms are commonly used
to classify the vast variety of phytogenic compounds,
mainly with respect to origin and processing, such as
herbs (flowering, nonwoody, and nonpersistent plants),
spices (herbs with an intensive smell or taste commonly
added to human food), essential oils (volatile lipophilic
compounds derived by cold expression or by steam or
alcohol distillation), or oleoresins (extracts derived by
nonaqueous solvents). Within phytogenic feed additives,
the content of active substances in products may
vary widely, depending on the plant part used (e.g.,
seeds, leaf, root, or bark), harvesting season, and geographical
origin. The technique for processing (e.g., cold
expression, steam distillation, extraction with nonaqueous
solvents, etc.) modifies the active substances
and associated compounds within the final product.