Xylazine does not induce retrograde flow of spermatozoa into the urinary bladder of sexually rested boars.

The effect of xylazine on the retrograde flow of spermatozoa from their storage sites in the epididymides and vasa deferentia into the urinary bladder of sexually rested boars was examined. The bladder of four boars was evacuated through a surgically implanted urinary catheter and the urine was examined for the presence of spermatozoa. Boars were then given an injection of 2.2 mg of xylazine per kilogram of body weight and, immediately thereafter, 500 ml of saline was infused into the urinary bladder. Approximately 50 ml of the post-treatment mixture of urine and saline, referred to as 'urine', was collected through the catheter at 5, 10, 15, 20, 30 and 45 min after the injection of xylazine, and examined immediately for the presence and motility of spermatozoa. At 60 min, the urinary bladder was evacuated and the remaining 'urine' was examined for the presence and motility of spermatozoa. None of the pre-xylazine urine and post-xylazine fractions of 'urine' had motile spermatozoa and xylazine did not increase (P > 0.1) the concentration and the number of spermatozoa in the post-treatment 'urine'. Thus, in contrast to other species, xylazine does not induce retrograde flow of spermatozoa into the urinary bladder of boars.