Are the vas deferens are cut and tied in a transurethral resection of the prostate (turp)?

No: No, they are not. The change in ejaculatory volume or the absence of ejaculate is related to retrograde ejaculation. After this type of surgery semen enters the bladder instead of being propelled forward during ejaculation. The semen is then evacuated from the bladder with the next void (urination).

Almost never: Used to be common for some urologists to tie of the vasa deferentia (plural) after open prostate surgery, which was associated with about 2% incidence of epididymitis & when fewer different antibiotics were in existence. Turp is associated with lower incidence of postoperative infection & catheters remain inplace for shorter time compared to open surgery. Thus no need for vasectomy with turp.