Artificial insemination with cryopreserved sperm from feline epididymides stored at 4 °C

Recovering and storing sperm from the epididymides of males of rare felidae is useful for preserving the species. The objective of the present study was to determine pregnancy rates following artificial insemination (AI) of frozen-thawed epididymal sperm, which were cryopreserved following low-temperature storage of the epididymides. In this study, these sperm were used for unilateral intrauterine AI (UIUAI) or unilateral intratubal AI (UITAI) using 40 × 106 and 10 × 106 sperm, respectively. The caudal epididymides of 17 cats were stored at 4 °C for 24 h after castration. Artificial insemination of seven female cats was performed on Days 3 or 4 (start of estrus = Day 1) by UIUAI, 20 h after injection of 100 IU hCG to induce ovulation. Furthermore, UITAI at 24 h (UITAI-24) or 30 h (UITAI-30) after hCG were also done (five cats per group). It was noteworthy that AI by UIUAI and UITAI-24 was performed before ovulation, whereas AI by UITAI-30 was performed after ovulation. Pregnancy rates were 28.6% (2/7) by UIUAI, 80% (4/5) by UITAI-24, and 20% (1/5) by UITAI-30. Litter size was one or two by UIUAI, and one to four by UITAI. Spontaneous abortion occurred on Days 25-30 of pregnancy in one of the two female cats pregnant following UIUAI, and in two of five female cats pregnant following UITAI. Based on the high pregnancy rate obtained with 10 × 106 sperm in the UITAI-24 group (AI performed before ovulation), we concluded that this was the most appropriate method for AI with frozen-thawed epididymal sperm after initial low-temperature storage of epididymides.