A tourniquet was placed at mid cannon bone on this cow's leg.

Lidocaine is being injected in the dorsal pedal vein.

What is expected to happen?

Sorry.  You chose C, but the correct answer is A. Anesthesia distal to tourniquet

Anesthesia distal to tourniquet.

This is an example of intravenous regional anesthesia, the anesthetic method of choice for most bovine digital surgical procedures.

It has similar results to a nerve block, but is easier to do with reliable results.

You need only one injection and no special knowledge of anatomy.

2% Lidocaine infuses down the venous system and anesthetizes the entire lower limb distal to the tourniquet within about 10 minutes.

The amount of lidocaine needed is typically 10-30 ml and should not exceed a total dose of 9 mg/kg.

Do not keep a tourniquet in place more than one hour.

Some references call this a "Bier" block, after the pioneering German physician August Bier, who reported on this form of anesthesia in 1908.

Refs: Guard, C, Musculoskeletal Disorders, in Disease of Dairy Cattle, Divers & Peek, 2nd ed. pp. 476-477, Pasquini and Spurgeon's Anatomy Dom An 11th ed. p. 497, Image courtesy Dr. Lisle George