Glutathione Peroxidase Activity In Grazing Dairy Cattle: Age And Seasonal Variations

This study was designed to evaluate the nutritional status of selenium, measuring the blood GSH-Px activity in dairy herds from the South of Chile. Blood heparinized samples were taken from 5 groups (calves, rearing heifers, heifers, dry cows, and early lactating cows) of 7 animals each, from 8 dairy herds in the Province of Valdivia, Chile (39 degrees S y 73 degrees W) in the autumn of 1995. Groups of heifers and early lactating cows from the same herds were sampled during the spring of that same year.A kinetic method was used to analyse blood GS H-Px activity. The mean and standard deviation of the values obtained were calculated. In order to compare the results among groups and between periods, the Kruskal-Wallis or Mann-Whitney statistical tests were used, as appropriate. The calves presented the highest values for blood GSH-Px activity while rearing heifers and heifers presented the lowest (P<0.01). In the rearing heifer and heifer groups there was an increase in the percentage of animals that presented low values of blood GSH-Px activity (30%). The blood GSH-Px activity of the dry period and early lactation groups was similar (P>0.01). A decrease in the GSH-Px activity was observed in heifers in spring, and the Values were lower than those observed in autumn (P<0.01).These results suggest that there are metabolic imbalances of selenium in dairy herds from the South of Chile; being grazing heifers the most affected.