title: Subclinical mastitis disrupts oocyte cytoplasmic maturation in association with reduced developmental competence and impaired gene expression in preimplantation bovine embryos.
abstract: Subclinical chronic mastitis was induced to examine the effects on oocyte developmental competence. Uninfected Holstein cows were intramammary administrated with serial (every 48 h for 20 days) low doses of toxin of Staphylococcus aureus origin (Gram-positive; G+), endotoxin of Escherichia coli origin (Gram-negative; G-) or sterile saline (control). Follicular fluid of toxin- and saline-treated cows was aspirated from preovulatory follicles and used as maturation medium. Oocytes harvested from ovaries collected at the abattoir were matured and then fertilised and cultured for 8 days. The percentage of oocytes undergoing nuclear maturation, determined by meiotic nuclear stages, did not differ between groups. Cytoplasmic maturation, determined by cortical granule distribution, was affected by both toxins (P < 0.05). The percentage of oocytes cleaving to 2- and 4-cell embryos and of embryos developing to the blastocyst stage was lower in both toxin-treated groups than in the control group (P < 0.05). There was no significant difference in the total cell number in Day 8 blastocysts among the groups; however, the apoptotic index was higher in both toxin-treated groups compared with control (P < 0.05). The relative abundance of prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclo-oxygenase; PTGS2) mRNA increased, whereas that of growth differentiation factor 9 (GDF9) decreased in matured oocytes. In addition, PTGS2 expression increased and POU class 5 homeobox 1 (POU5F1) expression decreased in 4-cell embryos developed from both G+ and G- oocytes. Thus, regardless of toxin type, subclinical mastitis disrupts oocyte cytoplasmic maturation and alters gene expression in association with reduced developmental competence.
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.|Corresponding author. Email: roth@agri.huji.ac.il.
authors.forename: Z
authors.initials: Z
authors.lastname: Roth
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Asaf
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.
authors.forename: O
authors.initials: O
authors.lastname: Furman
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Lavon
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Kalo
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot 7610000, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Wolfenson
authors.affiliation: Mastitis Laboratory, The Veterinary Institute, Bet Dagan 50250, Israel.
authors.forename: G
authors.initials: G
authors.lastname: Leitner
keywords: dairy cows; fertility; mammary gland