Gonadal and extra-gonadal sperm reserves were determined for nine 36-month-old Holstein bulls 23 weeks after unilateral vasectomy. The postoperative treatment groups, of three bulls each, were subjected to the following regimen: sexual rest, two ejaculates per week, and eight ejaculates per week for the last 20 weeks before slaughter. The correlation between gonadal reserves and testis weight was highly significant, +0·70. Gonadal reserves averaged 15·2 ± 0·8 × 109 and were not affected by either unilateral vasectomy or pre-slaughter ejaculation frequency. Sperm reserves in the caput and corpus epididymis also were unaffected by treatments. Sperm reserves in the cauda epididymis on the intact side were similar in the sexuallyrested and twice-weekly-ejaculated bulls. In bulls ejaculated eight times weekly, the cauda on the intact side contained 24% fewer spermatozoa just prior to ejaculation than if the bulls had been sexually rested. In eight of the nine bulls, sperm reserves in the cauda epididymis on the vasectomized side averaged 22·0 × 109 spermatozoa as compared to 11·4 × 109 in the contralateral cauda; an average of 17·8 × 109 spermatozoa accumulated in the ductus deferens just proximal to the site of vasectomy. In the other bull, the cauda epididymis on the vasectomized side contained 77·4 × 109 spermatozoa but there was no accumulation in the ductus deferens. After 23 weeks, some spermatozoa were found distal to the site of ligation in all nine bulls.
There appears to be a reciprocal relationship between sperm resorption and the total number of spermatozoa removed by collection and masturbation. The apparent rate of sperm resorption in the epididymis on the intact side of three bulls collected eight times weekly was 57%. In the vasectomized sides of nine bulls, it was greater than 96%. The rate of sperm resorption was postulated to be dependent upon the number of spermatozoa present in the cauda epididymis.
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