An essential or non-essential element or compound in a food or feed is known as a(n):

In the context of animal nutrition, the term that best fits the description of an essential or non-essential element or compound in a food or feed is "nutrient." Nutrients encompass a broad range of substances that provide essential nourishment for the maintenance of body functions, growth, and overall health. These include carbohydrates, proteins, fats, vitamins, and minerals.

Essential nutrients are those that the body cannot synthesize on its own and must be obtained from the diet, whereas non-essential nutrients can be produced by the body. This inclusive definition makes "nutrient" the correct choice, as it encompasses both essential and non-essential components necessary for health.

Other choices describe specific aspects of nutrition: minerals are a type of nutrient that are inorganic and play numerous roles in bodily functions; calories are a measure of energy rather than a substance; and enzymes are proteins that catalyze biochemical reactions and are not classified as nutrients themselves. Therefore, "nutrient" is the term that accurately reflects the entire category of essential and non-essential elements or compounds in food or feed.