Relationship between the level of N-acetyl-β-D-glucosaminidase (NAGase) in bovine milk and the presence of mastitis pathogens

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Abstract
Summary: Changes in the level of the tissue damage marker enzyme, N-acetyl-β-D-glucosaminidase (NAGase) in quarter fore milks were found to be related to the presence and types of pathogenic bacteria present and to somatic cell counts (SCC). Minor pathogens (coagulase-negative staphylococci, Corynebacterium bovis) elicited a mild SCC increase (from a mean of 243 × 103/ml in healthy quarters to 504 × 103/ml in infected quarters) with marginal tissue damage (mean NAGase activity increased from 21 in healthy quarters to 28 in infected quarters). Major pathogens (i.e. Staphylococcus aureus, Streptococcus agalactiae, Str. dysgalactiae and Str. uberis) caused more severe tissue damage (mean NAGase of 48) and SCC increases (mean, 2803 × 103/ml). The NAGase test could also be used effectively on composite milk samples where regular monthly NAGase analysis was able to identify correctly 74% of animals having infected quarters. The possibility of combining SCC and NAGase data in order to give a more definite diagnosis of bovine mastitis is discussed.