What is the function of a livestock cane used while showing cattle?

A livestock cane, also known as a show stick, serves as a driving tool during cattle shows. Its primary function is to guide and position the animal effectively in the show ring, helping the handler to control the cattle's movements and posture. Handlers use the cane to gently direct the cattle into a favorable position, ensuring they stand correctly and display their best conformation to judges. The use of a livestock cane allows for precise communication between the handler and the animal, creating a more positive impression during the performance and evaluation.

In the context of the other choices, a feeding tool would typically be used for providing food to the animals, which is unrelated to showing. A measuring tool is designed for gauging size or weight, not for controlling an animal in a competitive setting. A watering tool would focus on providing hydration, rather than the positioning or movement required in a show environment. Hence, the selection of the driving tool as the function of a livestock cane is accurate based on its specialized use during cattle shows.