All of the surgeries I do on cows is done on the farm - in a barn or sometimes out in the field. It depends on what surgery is being done, but I usually keep the cow standing if possible. We remove the hair over the site, and scrub and prep the area like you would do any surgery. I keep packs of sterile instruments in my truck, with sterile gloves and other surgical supplies. I do lay the cow down if I doing surgery on her hooves or legs.
Cows are sometimes uncooperative patients.
But with some help from the farmer, I can usually get the job done. It really just depends on the person. If there is a wound or other problem that must be cleaned or treated, it is important to remove the hair from that area. If you allow hair to fall back into a wound, it can spread more bacteria and reinfect the wound and slow its healing.