Mastitis is associated with decreased fertility in dairy cows. In the current study, we created an experimental model to simulate shortterm mastitis by a single intramammary administration of Gram-negative endotoxin of Escherichia coli origin (G-), or Gram-positive toxin of Staphylococcus aureus origin (G+), to examine the effect of mastitis on oocyte developmental competence. Healthy Holstein cows were synchronized, and follicular fluid (FF) of cows treated with G+ or G-and of uninfected cows (controls) was aspirated from the preovulatory follicles by transvaginal ultrasound procedure. The aspirated FF was used as maturation medium for in vitro embryo production. The distribution of matured oocytes into different cortical granule classes and meiotic stages was affected by G-administration (P<0.05) but not by GC administration. The proportion of oocytes that cleaved to two-and four-cell stage embryos (44 h postfertilization)was lower in bothGCandGKgroups than in controls (P<0.05). Blastocyst formation rate (7-8 days postfertilization) was lower in the G-group (P<0.05) and numerically lower in the G+ group compared with their uninfected counterparts. The total cell number in blastocysts did not differ among groups; however, the apoptotic index was higher in the G+ group (P<0.05), but not in the G-group, relative to controls. Examining mRNA relative abundance in oocytes and early embryos revealedmastitis-induced alterations in PTGS2 (COX2), POU5F1, and HSF1 but not in SLC2A1 (GLUT1) or GDF9. Results indicate a differential disruptive effect of mastitis induced by GK and GC on oocyte developmental competence in association with alterations in maternal gene expression.