Table 4.

Main biological process related to calving and involved in the development of the oxidative stress status in dairy cows during the transition period: their site of occurrence, their biological function and the mechanism by which they contribute in altering redox status

Biological process	Site	Function	Mechanism	References
Cellular respiration Colostrogenesis	All tissues Mammary gland	Conversion of nutrient to energy aimed to face requirements for milk synthesis and secretion	ROM1 are formed in mitochondria as byproduct of electron transport chain and their massive production deplete antioxidant systems	Bell, 1995; Hodgkinson et al., 2007; Sordillo et al., 2007; Valko et al., 2007; Sordillo and Aitken, 2009
Fatty acid metabolism	Liver		ROM1 are formed in peroxisome consequently to beta-oxidation	Drackley, 1999; Grum et al., 2002
Respiratory burst	Phagocytes	Kill microbial pathogens during inflammation	ROM1 are formed in phagocytes from NADPH2 oxidase system; Macrophages produce nitric oxide as a cytotoxic agent; Neutrophils releases hypochlorous acid through the myeloperoxidase activity, generating di-tyrosil residues from serum albumin	Babior, 1999; Dedon and Tannenbaum, 2004; Bordignon et al., 2014
Oxylipid biosynthesis	Cellular membranes	Regulation of inflammatory process and immune response	Lipid peroxide and superoxide anion are byproduct of the oxidative reactions of PUFA3 triggered by COX4, LOX5 or cytochrome P450	Raphael and Sordillo, 2013
Reduced dietary intake	Gut, tissue and blood	Adaptation to physiological imbalance related to calving	Reduced plasma concentrations of serum-derived micronutrients (i.e., vitamins and minerals) with antioxidant properties	Spears and Weiss, 2008; Sordillo and Mavangira, 2014
Increased utilization of antioxidant systems	Blood and tissues	Facing metabolic stress occurred in transition period; Satisfying increased vitamins requirements of growing fetus
Lipomobilization and triglycerides deposition	Liver cells	Supply to growing energy demand	Liver damage and dysfunction reduce plasma cholesterol and high-density lipoproteins, which bound paraoxonase, an important antioxidant enzyme, to the blood	Turk et al., 2005
Inflammatory status		Face tissue damages and infections related to calving

¹Reactive oxygen metabolites.

²Nicotinammide adenine dinucleotide phosphate.

³polyunsaturated fatty acids.

⁴Cyclooxygenase.

⁵Lipoxigenase.