15 Pregnancy loss until 120 days of Nellore clone pregnancy

It is remarkable that mammalian somatic cell nuclei can form whole individuals if they are transferred to enucleated oocytes. Advancements in nuclear transfer technology can now be applied for livestock genetic improvement and multiplication, rescue of endangered species, and assisted reproduction and tissue engineering in humans. Pregnancy loss is observed at various stages after transfer of cloned embryos from somatic cells to recipients. The objective of this study was to evaluate pregnancy outcomes and failures until 120 days of gestation in commercial Nellore clone production. The data were collected in a commercial clone production company in Uberaba, Minas Gerais State, Brazil, from 2019 to 2020. The Nellore clones were produced with nuclei obtained from skin somatic cells and oocytes collected by ovum pickup (OPU) from Nellore cows. The Nellore clones were transferred to cross-bred recipients (Nellore × Angus), synchronised with a protocol based in progesterone and oestradiol at day seven after expected oestrus. The first pregnancy diagnosis was performed between 30 to 60 days after expected oestrus by transrectal ultrasound examination. To determine the pregnancy outcome, the number of pregnancies was divided by the total number of transferred clones. Pregnancy was evaluated again between 60 to 90 and 90 to 120 days, and pregnancy loss was considered to occur when a cow who was diagnosed as pregnant on the first exam failed to remain pregnant in a subsequent exam. Blastocysts were transferred to 2,227 recipients; 821 recipients become pregnant on days 30 to 60 (36.87%). Pregnancy loss at 60 to 90 days was 29.48% (242/821) and 37.51% (308/821) at 90 to 120 days. At 120 days of gestation, 513 (62.49%) recipients remained pregnant. The reported data reflect the improvement of the cloning process and in vitro production over the past several years. However, there are still opportunities to improve clone production efficiency.