Sonic didn't have painkillers, I honestly don't believe that it is necessary for a very minor procedure like a neuter, muscle tissue hasn't been involved so there isn't bruising around the incision. It heals completely within 2 days. I'm really not in favour of giving painkillers for something that minor and quickly healing - drugs put a strain on the liver, and it simply isn't necessary for a straightforward neuter.
Radar had a long-acting painkiller/sedative injection after his neuter and hernia op, but the hernia surgery is worse than a spay, and he did need something to take the edge off that first night. I asked the vet about oral pain medication to take home with me, and the vet said that if he felt no soreness at all he wouldn't know to 'pace himself' and could accidentally rip the stitches out or overdo it without feeling the damage he was doing. He didn't need them anyway when it came down to it!
If there is any visible pain or discomfort worse than a little tenderness when they sit down, then something isn't right.