Frequency and Occurrence of Late-Gestation Losses from Cattle Cloned Embryos

TLDR

Nuclear transfer from somatic cells remains inefficient, largely because of high fetal loss after transfer. The study aimed to determine how the type of donor cells used for cloning affects in‑vivo development. Researchers monitored pregnancies by repeated ultrasonography and maternal PSP60 serum assays to detect late‑gestation losses and assess their frequency relative to embryo cloning and IVF. Late‑gestation losses were observed in 43.7 % of adult somatic clones and 33.3 % of fetal somatic clones, versus 4.3 % after embryo cloning and none in IVF, with elevated PSP60 levels and placental abnormalities preceding loss, suggesting that PSP60 monitoring and ultrasonography can improve care of cloned pregnancies.

Abstract

Nuclear transfer from somatic cells still has limited efficiency in terms of live calves born due to high fetal loss after transfer. In this study, we addressed the type of donor cells used for cloning in in vivo development. We used a combination of repeated ultrasonography and maternal pregnancy serum protein (PSP60) assays to monitor the evolution of pregnancy after somatic cloning in order to detect the occurrence of late-gestation losses and their frequency, compared with embryo cloning or in vitro fertilization (IVF). Incidence of loss between Day 90 of gestation and calving was 43.7% for adult somatic clones and 33.3% for fetal somatic clones, compared with 4.3% after embryo cloning and 0% in the control IVF group. Using PSP60 levels in maternal blood as a criterion for placental function, we observed that after somatic cloning, recipients that lost their pregnancy before Day 100 showed significantly higher PSP60 levels by Day 50 than those that maintained pregnancy (7.77 ± 3.3 ng/ml vs. 2.45 ± 0.27 ng/ml for normal pregnancies, P < 0.05). At later stages of gestation, between 4 mo and calving, mean PSP60 concentrations were significantly increased in pathologic pregnancy after somatic cloning compared with other groups (P < 0.05 by Day 150, P < 0.001 by Day 180, and P < 0.01 by Day 210). In those situations, and confirmed by ultrasonographic measurements, recipients developed severe hydroallantois together with larger placentome size. Our findings suggest that assessing placental development with PSP60 and ultrasonography will lead to better care of recipient animals in bovine somatic cloning.