Relationship between late embryonic mortality and the increase in plasma advanced oxidised protein products (AOPP) in dairy cows Pietro Celi A , Mariacristina Merlo B , Laura Da Dalt B , Annalisa Stefani C , Olimpia Barbato D and Gianfranco Gabai B,E A Faculty of Veterinary Science, University of Sydney, Franklin Lab, Narellan, NSW 2567, Australia. B Department of Experimental Veterinary Science, University of Padova, Agripolis, 35020 Legnaro (PD), Italy. C Istituto Zooprofilattico Sperimentale, Agripolis, 35020 Legnaro (PD), Italy. D Department of Biopathological Veterinary Science, Faculty of Veterinary Medicine, University of Perugia, via San Costanzo, 4 – 06126 Perugia, Italy. E Corresponding author. Email: gianfranco.gabai@unipd.it Abstract. The involvement of protein oxidation in embryonic mortality (EM) has been poorly investigated in cows. Advanced oxidation protein products (AOPP) are markers of protein oxidation generated by activated neutrophils and involved in inflammation. The aim of this work was to study AOPP in cow plasma and their relationship with late EM. The outcomes of 158 artificial inseminations (AI) were examined in 72 cows, which were classified ex post on the basis of blood progesterone and pregnancy-associated glycoprotein concentrations and clinical confirmation of pregnancy into the following categories: (1) positive (AIþ, resulted in pregnancy, n ¼ 58), (2) negative (AIÀ, did not result in pregnancy, n ¼ 86) and (3) embryonic mortality (EM, n ¼ 14). Plasma protein fractions, malondialdehyde (MDA), total glutathione and AOPP were measured at AI (Day 0) and on Days 15, 28, 35, 45 and 60. MDA was significantly higher in EM than AIþ and AIÀ animals on Day 45, and than AIþ animals on Day 60 (Po0.05). Mean plasma AOPP concentrations were significantly higher in the EM group (Po0.01) and the ratio of AOPP : albumin was significantly higher in the EM group on Days 15, 28, 45 and 60 (Po0.05). Based on the temporal pattern of the AOPP : albumin ratio, we propose that oxidative stress is implicated in and may possibly be a cause of EM. Additional keywords: inflammation, protein oxidation. Introduction Embryonic mortality (EM) represents a major limitation to fertility in the modern dairy system. In particular, late EM occurs between Days 24 and 42 after artificial insemination (AI) and accounts for ,5–10% of pregnancy failures (Mann and Lamming 1999). Despite extensive investigation, the causes of EM are not fully understood, and several factors have been suggested as being implicated in this phenomenon: poor oocyte quality (Perry et al. 2002), inadequate uterine environment (Gray et al. 2001), asynchrony between maternal endocrinology and embryo development (Roberts et al. 1996; Goff 2002; Johnson et al. 2003) and maternal failure to respond to embryonic signals (Hansen 2002; Green et al. 2005). Reactive oxygen metabolites (ROMs) and oxidative stress (OS) seem to have a role in the cause and progression of several reproductive events in both humans and animals, such as fertilisation and early embryo development. Indeed, it seems that OS is responsible for embryo damage that can then result in embryonic death (Gue ´rin et al. 2001; Agarwal et al. 2005; Fujii et al. 2005). OS is the result of an imbalance between the production of ROMs and the neutralising capacity of antioxidant mechanisms (Sies 1991; Castillo et al. 2005; Tanaka et al. 2007); an excess of ROMs leads to DNA damage, lipid peroxi- dation, cell membrane alteration and protein damage (Sugino 2006). Radical-mediated protein oxidation is a complex process that may generate multiple products from amino acid residues and the peptide backbone. Oxidised proteins are often functionally inactive and they can be either more, or less, susceptible to protease breakdown, leading to accumulation (Dean et al. 1997). In addition, they may activate the immune reaction and the production of auto-antibodies (Shanti et al. 1999; Kurien et al. 2006; Chou et al. 2008). CSIRO PUBLISHING www.publish.csiro.au/journals/rfd Reproduction, Fertility and Development, 2011, 23, 527–533 Ó CSIRO 2011 10.1071/RD10268 1031-3613/11/040527