Abstract
The objectives of this study were to obtain morphological data for normal spermatozoa and to investigate seasonal changes (the early, mid- and post-mating seasons) in abnormal morphology of spermatozoa and the characteristics of semen in Japanese black bears. Semen was collected by electroejaculation from 34 captive male Japanese black bears a total of 74 times. Length of head, width of head, length of midpiece and total length of the spermatozoa were 6.3 ± 0.4, 4.5 ± 0.3, 10.4 ± 0.7 and 69.6 ± 3.1 μm (mean ± SD; 20 semen, 200 spermatozoa), respectively. In the semen collected during the mid-mating season, ejaculate volume, ejaculate pH, sperm concentration, total sperm count, motility, viability and intact acrosomes were 0.46 ± 0.36 ml, 7.3 ± 0.4, 659 ± 644 × 106/ml, 214 ± 208 × 106, 82.9 ± 9.6%, 89.3 ± 9.5% and 97.0 ± 3.2% (mean ± SD; n=21, in ejaculate pH n=8), respectively. Sperm motility and viability in the early (n=7) and mid-mating (n=21) seasons were significantly higher than in the post-mating (n=8) season. The rates of detached heads in the early and mid-mating season were significantly lower than in the post-mating season. The main abnormal morphologies observed (mean ± SD%; n=23) were simply bent tail (19.9 ± 22.6), distal droplets (13.5 ± 11.7), proximal droplets (9.6 ± 7.8), teratoid spermatozoa (6.7 ± 10.7), knobbed acrosome (4.9 ± 8.6), acrosome damage (3.7 ± 2.8) and bent midpiece (3.7 ± 5.1). The data will be useful for artificial breeding and further research on male reproductive physiology in this species.
