Single fixed-time laparoscopic intrauterine insemination as a tool to obtain low-diversity porcine embryos

Double fixed-time insemination after ovulation induction is commonly used in pigs to obtain in vivo produced embryos at defined stages of development for downstream biotechnological applications. However, variations in the time of ovulation and fertilisation of the ovulated oocytes by spermatozoa, mainly in one of the inseminations, can cause diversities in embryo development. The aim of the present study was to reduce embryo diversity and to achieve a 'uniform outcome' of porcine embryo stages using single laparoscopic fixed-time insemination (LIUI). Altogether, 48 puberal German Landrace gilts were included in the study. Estrus of gilts was synchronized by 15-day long altrenogest (Regumate®) feeding and follicle development was stimulated with 850 IU eCG 24 h after the final altrenogest application. Ovulation was induced with 500 IU hCG 80 h after eCG. LIUI was performed 31 h after hCG treatment. Gilts under general anaesthesia were fixed in a dorsal position, a pneumoperitoneum was produced and three trocar cannulas were inserted into the abdomen for optics and instruments. Each uterine horn was carefully punctured 10-15 cm caudal from the utero-tubal junction with a 2.5 mm trocar. A 2.2 mm catheter was inserted about 3 cm into the uterine lumen and 20 ml of extended fresh boar semen (32.2 × 106 sperm cells/ml) were injected. Embryos were surgically flushed from the genital tract two (Day 2) and three (Day 3) days after insemination. Altogether, 778 oocytes/embryos were recovered (recovery rate 68 ± 17%); 45 of 48 gilts (93.8%) revealed fertilisation and 76.1% of the recovered embryos (n = 592) were at the 2- and 4-cell stage. On Day 2 (n = 22 gilts), a higher percentage of gilts (72.7%, P < 0.05) displayed only 2-cell embryos compared with gilts which had 2- and 4-cell (22.7%), or only 4-cell embryos (4.6%). On Day 3 (n = 23 gilts), the proportion of gilts with 2-cell, 2- and 4-cell, and only 4-cell embryos shifted to 4.3%, 0% and 95.7%, respectively (P < 0.05). The results of the present study demonstrate high rates of fertilisation and homogenously developed embryos after single fixed-time laparoscopic intrauterine insemination in gilts. Additionally, these results were achieved by inseminating a 60% lower number of sperm cells per insemination dose compared to usual doses used for transcervical insemination. In conclusion, LIUI can be recommended for the in vivo production of embryos in a homogeneous developmental stage, and also as an alternative method for low-dose insemination.