Evalution of the relationship between milk glutathione peroxidase activity, milk composition and various parameters of subclinical mastitis under seasonal variations

Abstract

The aims of this study were to evaluate the Glutathione peroxidase (GSH-Px) activity in milk, and various milk parameters [milk fat, milk protein, milk solids non-fat (SNF), somatic cell count (SCC), total bacteria count (TBC), electrical conductivity (EC)] in healthy dairy cows during lactation, and to demonstrate the significant correlations between GSH-Px activity, milk composition, SCC, TBC and EC under seasonal variations. The cows calving in January were assigned into the winter group (n = 30) while the other cows calving in August were assigned into the summer group (n = 30). Milk samples were collected weekly during lactation, and monthly average values of the parameters were determined. Although milk GSH-Px activity was variable during lactation, it was significantly higher in the winter group compared to the summer group of cows during the first five months of lactation (P<0.001). However, between the 6th and 10th months of lactation, GSH-Px activity was significantly higher in the summer group (P<0.001). In both groups of cows, GSH-Px activity was negatively correlated with SCC, TBC and EC during lactation. No correlation was found between GSH-activity and milk composition. In conclusion, the alteration of milk GSH-Px levels could be used as a diagnostic tool for monitoring udder health due to its relationship with the parameters of subclinical mastitis. Furthermore, cows calving in winter had higher GSH-Px activity than those calving in summer, especially during the first few months of lactation. These findings indicate that milk GSH-Px activity in cows during lactation could be influenced by seasonal variations.