ABSTRACT. Artificial insemination with frozen cauda epididymal sperm was performed in cats. Sperm were transmigrated from the epididymides in 10 male cats. The mean sperm motility and viability were 67% and 82.5%, respectively, and 11.6 × 10 7 sperm were recovered. The mean sperm motility after thawing was 24.0%. Eleven female cats received unilateral intrauterine insemination of 5 × 10 7 sperm, and the conception rate was 27.3% (3/11). This was the first case of conception obtained with frozen epididymal sperm in cats. KEY WORDS: artificial insemination, epididymal sperm, feline.J. Vet. Med. Sci. 65(3): 397-399, 2003 It has been demonstrated in many species that epididymal sperm have fertility in in vitro fertilization and artificial insemination (AI) [4,8,[11][12][13][14][15]25], and fertilization with frozen epididymal sperm was confirmed in pigs [11] and dogs [9].Freeze-storage of epididymal sperm is an important technique for gamete preservation of species, particularly for preservation of animals becoming extinct. As wild animals in the cat family are becoming extinct, we selected cats as an animal model.We have performed studies of reproductive techniques such as in vitro fertilization [5,6], embryo transfer [6,24], and AI [18,[20][21][22][23] in cats.With regard to feline epididymal sperm, studies of the qualities [1,2], state of fertility acquisition [2,3,12], and freeze-storage method [4,8,17] are progressing, and fertility of fresh epididymal sperm [12] and frozen semen [4,8] has been shown, but no in vivo study with frozen epididymal sperm has been performed. With frozen feline ejaculated semen, Platz et al.[16] and we [23] have succeeded in obtaining newborns by intravaginal and intrauterine insemination, respectively. Therefore, we froze epididymal sperm by the same method as for freezing ejaculated sperm and investigated the possibility of inducing conception by intrauterine insemination. It has been shown that frozen semen supplemented with Orvus ES Paste (OEP, Nova Chemical Sales Scituate, Inc., MA, U.S.A.) has superior properties after thawing semen without OEP in dogs [9] and pigs [7]. In this way, the usefulness of OEP was also investigated in this study.Animals: Ten male crossbred cats aged 1.0-3.3 years (mean: 1.9 ± 0.3, SE) were used. For AI, 11 female cats aged 2-4 years were used. The cats were kept in groups in an animal room measuring 4 × 7 m with temperature controlled to 23 ± 2°C. The animals were given commercial dry cat food (Hill's Feline Maintenance Dry, U.S.A.).Transmigration of sperm from epididymis: Surgically excised testis and epididymis were weighed. The epididymis was cut at the corpus into two equal parts. Each part was minced in 1 ml of egg yolk Tris-fructose citrate solution (EYT-FC) [23] to transmigrate the sperm. The solution was filtered through a stainless steel mesh (80 µm) and sperm were recovered. The time from excision of the epididymis to transmigration of the sperm was within 1 hr.Sperm quality test and freezing: The recovered sperm were examined by the gen...