Intravas injection of the Vasalgel was successfully accomplished in all 16 male subjects. All males on this study were housed with females for at least one breeding season, which for rhesus monkeys in the Northern Hemisphere is generally mid-September to mid-February [10]. However, our experience at CNPRC timed mating colony is that females can become pregnant from mid-September to mid-May. Rhesus females have menstrual cycles of approximately 28 days and have cycles most of the year with the exception of a few months in summer – generally June, July and August, thus males had extensive exposure to cycling females. The mean time (± SEM) of co-housing with females was 1.19 ± 0.14 years with a range of 5 months 14 days (0.45 years) to 2 years. The shortest duration began in early September and continued until mid-April (Male # 15), thus covering a complete breeding season. No conceptions occurred for any of the Vasalgel males. As detailed in Table 1, seven of the males (Male # 1 – 7) have been almost continually housed with intact females for two breeding seasons without conceptions. There were no systematic behavioral studies performed, but routine behavioral monitoring had observation of breeding behavior for all study males that were monitored.

Instillation of Vasalgel

Due to the viscous nature of Vasalgel, a significant amount of pressure was required to instill material into the narrow vas deferens. The use of a luer-lock syringe to prevent separation of the catheter from the syringe was required and application of a consistent level of pressure over 10 to 20 s proved to be the most successful method. Efficiency of application improved with surgeon experience handling the material and effectively manipulating the vas deferens to allow for smooth catheter placement.

Surgical complications

Incorrect placement

(Animal 3) During instillation of Vasalgel, the injection site of the left vas deferens appeared to have significant leakage. It was noted that there was potential damage to the wall of the vas deferens associated with infiltration of Vasalgel under the sheath. Due to the uncertainty of successful Vasalgel placement, a traditional vasectomy was performed on the side in question. The affected area of the left vas deferens was isolated, double ligated with Vicryl 3–0 and transected. Closure of the surgical site was the same as for Vasalgel sites. Vasalgel was successfully placed into the right vas deferens in the animal and no complications were observed.

Sperm granuloma

(Animal 10) During a routine sedation approximately 2 months post-operatively, a small (approximate 1 cm) opening near the right surgical site was observed. The associated tissue was erythematous and a mild amount of white, viscous discharge was present near the opening. It was determined cytologically to be a sperm granuloma and a surgical repair, resulting in a traditional vasectomy as described above, was performed on the right side. No further complications were observed.

Social trauma-surgical intervention

Animal 2 was admitted to the CNPRC indoor hospital for nonspecific trauma associated with bite wounds and lacerations to the right leg, left cheek and neck, 1 day after returning to his home cage, which was 7 daysays after Vasalgel placement. Examination revealed a firm swelling palpable at the left surgical site, extending into the scrotum. It could not be determined if the swelling was associated with trauma from fighting with other males, a sperm granuloma or a hydrocele. Although no external evidence of trauma to the genital area was found at the time of the physical examination, possible internal trauma from male-to-male aggression could not be definitely ruled out. Exploratory surgery was elected, resulting in an attempt to perform a traditional vasectomy as described above (using 4–0 Prolene) due to the presence of a hydrocele. The presumed vas deferens was submitted for histopathology. The histopathology revealed that the spermatic cord had multiple areas of pyogranulomatous inflammation admixed with free spermatids, fibrin and hemorrhage along the surface of the spermatic cord, confirming the presence of a left spermatic granuloma (Fig. 1). Adjacent to these areas, but not associated with any inflammation, were small irregular foci of basophilic to amphophilic granular to crystalline material presumed to be Vasalgel (Fig. 2). Thus, it appeared that the inflammation was associated with the presence of extraluminal sperm, rather than from the presence of Vasalgel. After reviewing the histopathology and medical report, it was determined that the presence of Vasalgel was incidental to the post-operative complications.

Fig. 1 Animal 2: Abundant collagenous stroma surrounded by pyogranulomatous inflammation (orange arrow), and fibrin (black star). The clear spaces represent areas that contained sutures (asterisk). In the center of the image, is a small globule of basophilic to amphophilic material (black arrow, presumed Vasalgel). H&E, 40x Full size image

Fig. 2 Animal 2: Same section as Fig. 1. In the center of the image, is a small, irregular globule of basophilic to amphophilic material (black arrow, presumed Vasalgel). There is no associated inflammation. Clear areas of sutures are noted (asterisk). H&E, 100x Full size image

To determine the comparative complication rate between Vasalgel placement and traditional vasectomy, 16 age-matched vasectomized adult rhesus monkeys were identified. As shown in Table 2, five out of the 32 vasa (15.6%) from traditionally vasectomized animals developed sperm granulomas.