Which of the following is not a category of feed additives?

Vitamins play a crucial role in animal nutrition, but they are classified as essential nutrients rather than feed additives. Essential nutrients, including vitamins, minerals, proteins, carbohydrates, and fats, are necessary for the growth, development, and overall health of animals. These nutrients must be provided in appropriate amounts through a balanced diet.

On the other hand, antibiotics, probiotics, and enzymes serve specific supplemental roles beyond basic nutrition. Antibiotics can promote growth and prevent disease in livestock, while probiotics help maintain gut health and improve digestion. Enzymes are added to enhance the efficiency of feed utilization and digestion. These categories are considered feed additives because they supplement the animal's diet with specific functional benefits that go beyond just providing necessary nutrients.