What is often employed when taking a blood sample from a small animal's leg vein?

Using a tourniquet when taking a blood sample from a small animal's leg vein is a common practice because it helps to engorge the vein, making it more prominent and easier to access with a needle. By applying a tourniquet, blood is temporarily pooled in the vessel, which increases the pressure and size of the vein. This technique is especially useful in small animals, where veins can be difficult to locate due to their size or because they may be more relaxed or collapsed.

The other options represent alternative methods or tools that may be found in veterinary practice but do not serve the same purpose in preparing for venipuncture. Local anesthesia may be used in some cases to minimize pain but is not standard for routine blood draws in most small animals. The Vacutainer system is a specialized device used to collect and transport blood, and while it is essential for the actual collection process, it does not assist in making the vein more accessible. The blood pressure cuff can also aid in locating veins but is less common compared to the tourniquet due to its design and application challenges in practice. Thus, the use of a tourniquet is the most effective and typical method employed for accessing leg veins in small animals for blood samples.