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Summary.

An intravenous injection of 10 i.u. oxytocin into rams 10 min before ejaculation increased the number of spermatozoa per ejaculate by 45%. The optimum dose was between 5 and 10 i.u. oxytocin and the optimum interval between the injection of oxytocin and ejaculation was 5 to 10 min. The increase in the number of spermatozoa per ejaculate was accompanied by increases in semen volume, and/or sperm concentration. The increase in the semen volume and total fructose per ejaculate suggested that oxytocin stimulated the accessory sex glands. Adrenaline injections had no effect on the output of semen.

Summary.

Contractions of the ram ductus deferens-epididymis and epididymis were recorded by cannulating these ducts and measuring the intraluminal pressure changes. The intravenous injection of 0·3 to 10 i.u. oxytocin or 10 to 40 μg adrenaline, or mechanically increasing the pressure within the ducts, stimulated contractions and increased the tonus in the ductus deferens-epididymis. The duration of the response to 2 to 10 i.u. oxytocin was 20 to 70 min. The response to adrenaline and low doses of oxytocin were of a much shorter duration. Vasopressin was 1/15th to 1/20th as potent as oxytocin.

The response to oxytocin was not inhibited by adrenaline, α- or β-blocking agents or by atropine. In contrast, an α-receptor-blocking agent (phentolamine) inhibited the response to adrenaline.

Copulation initiated contractions of the ductus deferens-epididymis which were similar to the response to intravenous adrenaline. Contractions continued for only a short period after the end of copulation, suggesting that there had been little or no release of oxytocin during copulation.

Summary.

Intravenous injection of oxytocin into rams immediately before collection of semen with an artificial vagina, resulted in an increase in the volume of semen and the number of spermatozoa per ejaculate. After 6 weeks, during which the rams received 35 i.u. oxytocin per week, the volume of semen and the number of spermatozoa per ejaculate declined to the level of the non-treated rams and this decline was maintained for the next 4 weeks. The percentage of abnormal spermatozoa in semen from rams treated with oxytocin increased significantly (P<0·001) in the 7th week. The concentration of fructose in the semen and the libido were not affected by oxytocin. When an electro-ejaculator was used for making collections, the volume of semen increased after oxytocin injection (P<0·05), with a maximum response at 10 i.u. oxytocin.

Oxytocin appeared to have an immediate stimulating effect on the ejection of spermatozoa and seminal plasma during emission and a long term adverse effect on spermatogenesis.

Summary. The timing of ovulations in 42 PMSG-treated ewes was determined by repeated endoscopy. The first ovulation occurred at a median time of 23·6 ± 0·5 (s.e.m) h after the onset of oestrus. The median interval between first and second ovulations was less than 1 h, and that between first and last ovulations was approximately 6 h.

In 59 untreated ewes, probit regression analysis was applied to the number of ovulations which were found by endoscopy to have occurred by 23, 25 and 27 h after the onset of oestrus. The median time of first ovulation was 25·5 ± 0·5 h after the onset of oestrus, this interval being similar in single- and twin-ovulating ewes. The median interval between twin ovulations was 1·2 ± 0·6 h. Ovulation occurred after the end of oestrus in at least 75% of ewes.