The recovery of epididymal sperm in animals is considered as one of the important tools to preserve high value or endangered species. However, there are no appropriate castrating indicators such as months of age in bull, sperm morphology, and motility, particularly in young Korean native bull (Hanwoo). Therefore, this study aimed to investigate sperm number, morphology, and motility of sperm in the epididymis tail of young Hanwoo bulls at 8 and 15 months of age. After castration, epididymal tails were collected and minced with blades to recover sperm. In experiments 1 and 2, sperm number, morphology, and motility were examined. Total number of sperm and percentage of normal sperm from bulls at 8 months of age was lower than that of bulls at 15 months of age after collection (P<0.05). Percentage of abnormal head, tail, proximal cytoplasmic droplet, dead and damaged acrosome of sperm from bulls at 8 months of age were higher than those of bulls at 15 months of age (P<0.05). In experiment 3, sperm motility from bulls at 8 and 15 months of age were examined before freezing and after thawing. Frozen-thawed sperm at 8 months of age showed low total motility and motile sperm with ≥ 25 μm/sec compared to those at 15 months of age and commercially-used sperm (P<0.05). In conclusion, sperm derived from the epididymal tail of bulls at 8 months of age showed high abnormal morphology and poor motility, which are not adequate for AI and IVF. On the other hand, sperm derived from the epididymal tail of bulls at 15 months of age showed high normal morphology and motility.

Introduction
 Materials and Methods
  Chemicals
  Evaluation of sperm motility by CASA
  Preparation of sperm staining and fixing solutions
  Staining and fixing of sperm
  Evaluation of sperm viability and morphology
  Experimental design
  Statistical analysis
 RESULTS
  Experiment 1
  Experiment 2
  Experiment 3
 DISCUSSION
 REFERENCES

• Sung-Sik Kang(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Sang-Rae Cho(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Ui-Hyung Kim(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Chang-Seok Park(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Hyeong-Cheol Kim(Hanwoo Research Institute of Animal Science, Rural Development Administration (RDA))
• Ki-Yong Chung(Hanwoo Research Institute of Animal Science, Rural Development Administration (RDA))
• Seok-Dong Lee(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Sun-Sik Jang(Hanwoo Research Institute of Animal Science, Rural Development Administration (RDA))
• Gi-jun Jeon(Hanwoo Research Institute of Animal Science, Rural Development Administration (RDA))
• Sidong Kim(Animal Genetic & Breeding Division, Rural Development Administration (RDA))
• Myeong-Suk Lee(Laboratory of Reproductive Physiology, Hanwoo Research Institute)
• Byoung-Chul Yang(Laboratory of Reproductive Physiology, Hanwoo Research Institute) Corresponding author