Summary. The 12- to 24-month-old Holstein bulls were electroejaculated twice on each of 3 days per week throughout the study. After a 2-week stabilization period and subsequent 2-week pre-treatment period, 7 bulls were given 50 i.u. oxytocin via the jugular vein 10 min before each first ejaculate for 10 weeks. The 7 control bulls were handled identically but did not receive oxytocin. All bulls were castrated at the end of the study. Oxytocin was without effect on spermatogenesis (P > 0·10). Oxytocin did not alter the total number of spermatozoa harvested per collection day (P > 0·10), but increased the number of spermatozoa in first ejaculates by an average of 34·2% (P < 0·025). Oxytocin did not affect sperm quality (P > 0·10) as judged by the motility of spermatozoa in fresh semen or by the motility or percentage of spermatozoa with intact acrosomes in thawed semen. It is concluded that 50 i.u. oxytocin enhanced sperm output in first ejaculates of electroejaculated bulls without altering daily sperm production or seminal quality.
Keywords: bull; spermatogenesis; sperm output; oxytocin; semen