78 Pregnancy association glycoproteins for assessment of pregnancy status in IVF embryo recipients

In cattle, embryo attachment and early placentation occur after Day 21 post-ovulation, characterized by the formation of bi- or multinucleated giant cells in the synepitheliochorial placenta. These cells synthesize pregnancy-associated glycoproteins (PAGs), which serve as markers for pregnancy detection, attachment, and early placentation. Traditional embryo transfer (ET) programs typically involve two pregnancy checks: the first at ~35 days of gestation and the second between 60 and 90 days. Notably, pregnancy loss for IVF embryos is ~15% or higher between these checks. This study aimed to evaluate whether monitoring PAG levels could serve as an early indicator of placental malfunction and potential abortion. As part of a commercial ET program, synchronized heifers received an IVF embryo on Day 7 of the estrus cycle (estrus = Day 0). A total of 151 heifers were sampled weekly at Days 29, 36, 43, 50, and 57. Blood samples were collected using Vacutainer® needles and purple cap tubes with EDTA and sent to Texas A&M Pregnancy Development Program Laboratory. A commercial sample-based pregnancy test (IDEXX Alertys Ruminant Pregnancy Test) was run following the manufacturer’s procedures. Samples with S-n < 0.3 were considered open; between 0.3 and 1.0, rechecks; and >1.0 were diagnosed as pregnant. Transrectal ultrasonography (US) was performed at Days 36 and 85. All open animals at US received a dose of PGF_2α following the dairy routine procedures. Between US (Days 36 to 85), heat detection was performed assisted by tail paint, and animals in heat were bred by AI. All data were tabulated in JMP® 16.0.0. to generate summary statistics and calculate pregnancy rates. The PAG-based pregnancy rates were found to be 47%, 45.6%, 36.2%, 27.2%, and 26.8% at Days 29, 36, 43, 50, and 57, respectively. In comparison, ultrasound results indicated that 34.4% of heifers were pregnant by Day 36 and 28.5% by Day 85. When evaluated at same gestation time (Day 36), of 52 pregnant heifers based on ultrasound, 51 were pregnant based on PAG (98%). Of 97 open heifers based on US, 80 were open based on PAG (82%). Of the 17 discrepancies in identifying open animals, nine had evidence of decreasing PAG levels between Day 29 and Day 36, supporting possible early embryo death. The remaining eight animals, showed increasing or sustained PAG levels between Day 29 and Day 36, suggesting possible US misdiagnosis. Based on US only, IVF pregnancies experienced 17% of loss between Day 36 and Day 85. Considering the nine animals that aborted based on US and heat check, PAG weekly monitoring detected the open heifers 21.6 days earlier than farm standard procedures. Unfortunately, the comparison of pregnancy losses between US and SBPT could not be performed because open heifers received PGF_2α after US pregnancy check. In summary, weekly PAG testing provided an earlier indication of pregnancy loss compared with routine ultrasound, potentially reducing open days in high embryo mortality situations such as IVF-ET.