Characteristics of captive Japanese black bears (Ursus thibetanus japonicus) semen collected by electroejaculation with different voltages for stimulation and frozen-thawed under different conditions

The Japanese black bear (Ursus thibetanus japonicus) is an endangered species in some areas of Japan, and semen collection and cryopreservation are important means to preserve genetic resources and prevent extinction. The aim of the present study was to improve the methods for electroejaculation and cryopreservation in these bears. We collected the semen from captive mature Japanese black bears during the mating season by the electroejaculation method using maximum stimulus voltages of 10 V (n = 9) and 7 V (n = 15), and compared the characteristics of fresh semen after collection. None of the variables examined (i.e. total sperm count, motility, viability, morphology, and rate of urine contamination) were statistically different between the two electro-stimulus voltages. After the semen obtained was cryopreserved, the effects of three different diluents (egg yolk–TRIS–citrate–glucose, egg yolk–TRIS–citrate–fructose, and egg yolk–TRIS–citrate–fructose–lactose–raffinose; n = 10) and two different incubation times (1–1 and 3–0 h of cooling–glycerol equilibration times; n = 12) on frozen-thawed spermatozoa. None of the variables examined (i.e. motility, viability and morphology) were statistically different among the three diluents and between the two incubation times. The results indicate that, in the collection and cryopreservation of Japanese black bear semen: (1) a maximum voltage of 7 V may be enough to obtain ejaculates; (2) the three diluents examined were useful; and (3) glycerol equilibration time may be omitted with prior cooling for 3 h.