The incidence and timing of pregnancy loss derived from timed artificial insemination or timed embryo transfer using fresh or frozen in vitro-produced embryos

Lactating Holstein-Friesian cows were randomly assigned to receive either timely artificially inseminated (TAI, n = 243) or timely embryo transferred (TET, n = 863) with a fresh or frozen in vitro-produced blastocyst following a protocol consisting off on day 0, cows received a 2-mL intramuscular injection of GnRH analogue (Ovarelin, 100 μg of gonadorelin diacetate tetrahydrate; Ceva Sante Animale, Libourne, France) and a progesterone-releasing intravaginal device (PRID Delta; 1.55 g Progesterone, Ceva). On day 7, a 5-mL intramuscular injection of PGF2α (Enzaprost, 25 mg of dinoprost rometamol; Ceva) was administered, followed by a second 5-mL injection of PGF2α on day 8 and removal of the PRID. On day 9.5 (32 hours  fter PRID removal), a second intramuscular injection of GnRH was give, and cows were either  inseminated 32h later (TAI) or received a blastocyst 7,5 days after the last GnRH injection. The blastocysts were derived from oocytes  collected from the ovaries of elite dairy donors (14 Holstein Friesian and 8 Jersey) and elite beef donors (21 Angus) using transvaginal ovum pick-up. Additionally, oocytes were collected from the ovaries of beef heifers of known pedigree  following slaughter at a commercial abattoir (n = 119). Blood samples were collected on day 7 from all cows to determine progesterone concentration, and from subsets of cows on day 18 (n = 524) and day 25 (n = 378) to determine mRNA abundance of interferon-stimulated gene-15 and pregnancy-specific protein B concentration, respectively, for early pregnancy diagnosis. Transrectal  ultrasonography was conducted to determine pregnancy status on days 32, 62, and 125 after synchronized ovulation. Parturition dates were recorded for all cows that reached term delivery.

The incidence and timing of pregnancy loss derived from timed artificial insemination or timed embryo transfer using fresh or frozen in vitro-produced embryos 36calving, at the day of calving, and at +7, +14, +28, and +55d after calving. All animals were evaluated for NEFA and BHB levels, while a complete biochemical analysis was performed for 45 animal per group (30 luriparous, and 15 primiparous). Differences in biochemical parameters were assessed with a linear mixed-effects model. A post hoc pairwise comparison was performed using Bonferroni correction. A logistic regression analysis was performed using blood BHB values (healthy, BHB<1.2 mmol/L; hyperketonemia, BHB≥1.2 mmol/L). The model considered the risk factors of treatment, time, parity, and season. A p-value<0.0532 was considered significant, whereas a 0.05≤p-value≤0.10 was considered a trend.

In conclusion, AI and fresh ET led to a higher probability of cows becoming pregnant and maintaining the pregnancy to term compared to frozen ET. Cows that were still pregnant on day 62 had a very high likelihood of maintaining the pregnancy to full-term parturition, regardless of treatment. Further work is needed to improve the likelihood of pregnancy establishment and reduce embryonic and fetal mortality following the transfer of a cryopreserved in vitro-produced embryo.