Bear in mind that your bowels will be rearranged in your stomach, so that the surgeon can get to your prostate. It will take time for them to settle back into place and normal peristaltic movement restored, almost inevitably resulting in constipation.
The last thing you want to do is be straining to defecate so soon after surgery, so try and eat high fibre foods for the couple of days before your op, and afterwards. On discharge I was given boxes of senna laxatives and Fybogel (isphagula husk), but fortunately they were not needed. Her Loveliness made good use of them subsequently.
The first post-operative fart is a relief, and a sign that things are getting back to normal!
Best of luck.