Changes in milk oxidative stress biomarkers in lactating dairycows with ovulatory and an-ovulatory oestrous cycles.

This study was conducted to evaluate changes in milk profiles of oxidative stress (OS)biomarkers in dairy cows with ovulatory and an-ovulatory oestrous cycles. Thirty healthy,cycling Holstein cows averaging 60 ± 17 days in milk, and producing 33 ± 6 kg of milkper day (the week before commencing the study) were enrolled in this study. Compositemilk samples were collected thrice weekly and assayed for the following OS biomarkers:lipoperoxides (LPO), biological advanced potential, superoxide dismutase (SOD), advancedoxidation protein products (AOPP), ceruloplasmin, glutathione (GSH), -carotene andglutathione peroxidase (GSH-Px). Milk samples were also tested for fat and protein compo-sition and the fat:protein ratio (FPR) was categorized as low (≤1.31), medium (1.32–1.56)and high (>1.57) to evaluate their main effect and the interaction effect of FPR and the weekof study on OS using linear mixed models with cow identification being a random factor.Cows with ovulatory oestrous cycles (n = 20) presented significantly greater SOD levels thancows that did not ovulate ((n = 10; P < 0.05). On the other hand, LPO, GSH-Px and GSH con-centrations were lower in ovulated cows compared to the an-ovulated cows (P < 0.05). Thehighest level of LPO and AOPP were noted at prooestrus phase while -carotene presentedthe lowest value at that phase of oestrous cycle. It could be postulated that the elevatedlevel of milk SOD and the observed lower level of LPO, GSH-Px and GSH in ovulating cowsmay be an essential event preceding the ovulatory response.