Efficacy and effects of short- and medium-term contraception in the commonmarmoset (Callithrix jacchus) using melengestrol acetate implants

This study examines the effect of melengestrol acetate (MGA) implants on re productive function and various biochemical parameters, ovarian activity, a nd uterine morphology in ten female common marmosets implanted for either 6 -8 or 19-21 months. Measures of body weight, concentrations of urinary gluc ose and blood liver enzymes were taken. Ovarian activity was assessed by an alysis of urinary progestin levels and ultrasound examinations of the ovari es. Ultrasonography was also used to evaluate uterine morphology. MGA was h ighly effective in preventing pregnancies in the study animals. No changes in biochemical parameters were found; however, seven females developed a su bstantial weight gain during the study. Follicular development was not supp ressed, as indicated by the presence of antral follicles, luteinized struct ures, and elevated urinary progestin levels. The uteri of the MGA-treated s ubjects were moderately enlarged with a thickened endometrium that showed a marked change in structural appearance indicative of hypertrophy and decid ualization. After implant removal these changes quickly disappeared and all females ovulated within 3 weeks and conceived within 4 months post-treatme nt. MGA appears to be an acceptable contraceptive in the marmoset, although non-steroidal methods should be evaluated as possible potential alternativ es.