[Annual sperm concentration variation in semen collected by electroejaculation in the cynomolgus monkey (Macaca...

To observe annual sperm concentration variations in the cynomolgus monkey, semen samples from four cynomolgus monkeys were individually collected by the rectal probe electroejaculation technique every two weeks throughout an experimental period of two to three years. The annual variation in mean values of semen volume and sperm concentration in each animal examined were expressed as 0.10 to 0.16 ml and 154.54 to 267.17 x 10(6) sperm/ml of semen, respectively. The annual sperm concentration variation in samples collected from each animal was between 10(7) and 10(9) sperm/ml of semen. It was observed that the percentage of active spermatozoa ranged from 60 to 80 per cent, and correlated with both the sperm concentration and the semen volume. These results suggest that annual variation in sperm concentrations of semen collected by electroejaculation is due to differences in the contraction of muscles adjacent to the accessory genital gland and ampulla elicited by electrical stimulation.