Influence of mastitis on D-amino acid content of milk.

The California Mastitis Test was used as an indicator of mastitis in this study. Five cows were chosen for each of the five test scores (from 0 = healthy to 4 = severe mastitis). Milk samples were analyzed for free AA and free D-AA. The contents of free AA, free D-AA, and the ratio of free D-AA to free AA increased significantly as the California Mastitis Test score increased. The free D-AA content of foremilk (first milk jets) from healthy cows (test score = 0) was approximately five times that in samples drawn later from the same udders. Contents of free AA and free D-AA were highly associated with test score and udder inflammation. Very low concentrations of free D-AA are normal for raw milk. Higher concentrations of free D-AA could be attributed to inclusion of foremilk and milk from cows having subclinical mastitis in the bulk tank milk.