Which of the following best describes a "complete feed"?

A "complete feed" is characterized as a feed that provides all necessary nutrients required for an animal's growth, maintenance, and overall health without the need for additional supplementation. This definition emphasizes that a complete feed contains a balanced formulation of carbohydrates, proteins, fats, vitamins, and minerals tailored to meet the specific dietary requirements of the animal.

In contrast, a feed containing only grains would lack essential nutrients such as proteins, vitamins, and minerals. A feed that lacks essential nutrients would not meet the basic nutritional needs of the animal, which can lead to deficiencies and health problems. Similarly, a feed typically used as a supplement is not complete on its own, as it is generally designed to enhance or correct specific dietary deficiencies rather than serve as the sole source of nutrition. Therefore, the characteristic that defines a complete feed is its comprehensive provision of all necessary nutrients, making it the appropriate answer.