Milk Pathogens in Correlation with Inflammatory, Oxidative and Nitrosative Stress Markers in Goat Subclinical Mastitis

SIMPLE SUMMARY: Demand for goat milk is rising worldwide due to its nutritional characteristics. Inflammation of the mammary gland in goats is one of the most frequently encountered conditions in dairy farms, and it is associated with a decrease in milk quality and changes in milk composition. The aim of this study was to establish parameter levels suggestive of subclinical mastitis by analysing correlations between pathogens and biochemical parameters in goat milk. We collected 76 milk samples (Carpathian goat breed) from one Transylvanian farm in Romania, and we observed that milk from infected mammary glands had a significantly increased somatic cell count and enzymatic activity (lactate dehydrogenase and β-glucuronidase). Milk positive for bacterial growth was associated with oxidative stress, with high concentrations of antioxidant enzymes and oxidation products, as well as oxidative DNA damage. These changes tended to depend on the category of microorganisms isolated from milk samples, some of them being human pathogens, thus posing a threat to public health. According to the present results, assessment of SCC correlated with any of the evaluated biochemical markers, such as inflammatory enzymes, oxidative stress markers and/or oxidative DNA damage indicator, could be used in the early detection of mastitis in farms, especially when important pathogens are involved. ABSTRACT: Goat mastitis is still frequently diagnosed in dairy farms, with serious consequences on milk quality and composition. The aim of this study was to establish correlations between milk microorganisms and biochemical parameters in goats with no signs of clinical mastitis. Thus, 76 milk samples were collected from a dairy goat farm, Carpathian breed, followed by microbiological, molecular (16S rRNA sequencing) and somatic cells analysis, determination of lactate dehydrogenase (LDH), β-glucuronidase, catalase (CAT), glutathione peroxidase (GPx) activity, total antioxidant capacity (TAC), nitric oxide (NO) and lipid peroxides (LPO) using spectrophotometry and the ELISA method for 8-hydroxy-deoxyguanosine (8-OHdG) as the oxidative DNA damage indicator. Samples positive for bacterial growth showed a significant (p < 0.05) increase in the number of somatic cells, LDH and β-glucuronidase activity, as well as higher levels of CAT, GPx, NO, LPO and 8-OHdG compared with pathogen-free milk whereas TAC was lower in milk from an infected udder. These findings suggest that subclinical mastitis is associated with increased enzymatic activity and induction of oxidative stress. Nevertheless, changes in biochemical parameters tended to vary depending on the pathogen, the most notable mean values being observed overall in milk positive for Staphylococcus aureus.