Factors affecting outcomes of embryo transfer in dromedary camels: A retrospective study

The present study aimed to use a comprehensive approach for evaluating 12 factors related to embryo quality (shape, size and transparency), donors (age, ET type, number of recovered embryos and day of uterine flushing), recipients (age), males (age and individual variations) and environment (season and year) which could affect the outcome of ET in terms of pregnancy (PR) and pregnancy losses in dromedary camels. During three breeding seasons, 116 donor females were mated repeatedly at 12- to 14-day intervals by fertile male camels (n = 33) without stimulation of the ovaries (WSPO). Superovulation (SPO ET) regimen was applied for each donor female twice or thrice per season. In the occasions of applying superovulation regimen, donor females having an ovulatory follicle were mated instead of GnRH administration and superovulation regimen was applied 4 days post-mating (MIX ET). The uteri of all donor females were flushed at Day 8 or 9 post-mating, and a total of 2,095 embryos were recovered and transferred individually to 924 recipient females. Pregnancy diagnoses were conducted at Day 10 after ET (Days 18-19 of gestation) by using progesterone assay and by transrectal ultrasonography (TRU) at Days 30 and 60 of gestation. By using logistic regression analysis, transparency of embryos and age of recipient females had significant effects on PR at Days 18-19 (p < .01), 30 (p < .01) and 60 (p < .01; p < .05, respectively) of gestation. The shape of embryos had significant effects on the PR at Days 30 (p < .05) and 60 (p < .01) of gestation. Type of ET and the breeding season (year) had significant (p < .05) effects on the PR at Day 30, while day of flushing had the same effect on PR at Day 60. Regarding the pregnancy losses, transparency and shape of the embryo, type of ET, breeding season had significant (p < .05) effect on the late embryonic mortalities (LEM) and shape and season of year had significant (p < .01 and p < .05, respectively) effect on LEM/early foetal mortalities (EFM). Regarding male individual factor, there was a tendency for a significant (p = .055) effect of male camels on the PR at Days 18-19 and rate of LEM. In conclusion, transferring a spherical, transparent or a large-sized embryo (>750 µm) into recipient females ageing between 8 and 11 y could greatly improve the PR from Days 18 to 60 of gestation. Also, embryo recovered from donor females with Mix ET type or embryos sired by certain male camel or at Day 8 post-mating of the donor could improve the 2-month PR. In addition, transferring a transparent or spherical-shaped embryo or embryos recovered from donor females with SPO or Mix ET could reduce the pregnancy losses during the first 2 months of pregnancy.