Developmental and transcriptomic alterations in bovine blastocysts derived from oocytes of donors exposed to toxic tall fescue.

Fescue toxicosis, caused by the ingestion of ergot alkaloids present in endophyte-infected tall fescue (E + ), is associated with impaired reproductive performance in beef cattle. Because early embryonic development depends on maternally derived RNAs and proteins accumulated during oocyte maturation, disruption of oocyte contents by ergot alkaloids may affect embryonic development. This study evaluated the effects of maternal exposure to E + on reproductive performance and blastocyst gene expression in beef heifers. Twenty-four commercial Angus heifers were assigned to either E + (n = 12) or endophyte-free (E - ; n = 12) tall fescue diets for 49 days. At the end of the trial, follicles were aspirated to assess oocyte recovery and quality and to produce embryos by in vitro fertilization. Eight blastocysts (n = 4/group) were subjected to RNA sequencing and aligned to the ARS-UCD1.2 genome. Normalized gene expression counts were compared between groups to identify differentially expressed (DE) genes. Exposure to E + reduced the number of oocytes recovered, viable oocytes, and cleaved embryos compared with controls (P < 0.05), with the number of blastocysts also tending to be lower in the E + group (P = 0.096). Transcriptomic analysis identified 79 DE genes (FDR < 0.05), all of which were upregulated in E + embryos and are associated with development, extracellular matrix organization, complement and coagulation cascades, and stress responses. To our knowledge, this is the first study to support the hypothesis that preconception exposure to ergot alkaloids compromises oocyte competence, leading to inherited molecular alterations that impair early embryonic development.