Which of the following is not one of the six essential nutrients required by horses?

Horses require a balanced diet that includes six essential nutrients for optimal health and performance: water, carbohydrates, proteins, fats, vitamins, and minerals. Among these nutrients, carbohydrates are a crucial source of energy, and while sugars (a type of carbohydrate) provide energy, they are not classified as one of the six essential nutrients on their own.

Vitamins help regulate metabolic functions and are essential for maintaining health, while minerals are important for various bodily functions, including bone formation and enzymatic processes. Water is fundamental because it constitutes a significant part of a horse's body and is vital for almost every biological function.

In summary, while sugars contribute to energy intake, they do not fall under the category of the six essential nutrients required by horses, which is why this answer is accurate.