Measurement of the enzyme N-acetyl-beta-D-glucosaminidase for detection of subclinical mastitis in a random sample of bulk tank milk in Prince Edward Island

The objective of this study was to compare the fluorometric and the colorimetric methods of N-Acetyl-$\beta$-D-Glucosaminidase (NAG) measurement in bulk tank milk (BTM) as indicators of subclinical mastitis in dairy cattle.

Observation of an effect of time in frozen storage on NAG activity was not significant for the fluorometric method and was significant for the colorimetric method in this study. Enzyme activity determined by the fluorometric methods was less affected by days in storage.

The pattern of the frequency distributions of NAG and SCC in BTM were distinctly different. The fluorometric method of NAG measurement had a stronger association with SCC than the colorimetric method.

The range of NAG(F) in the BTM collected in this study was 2-7 U/mL. Threshold value NAG(F) $>$ 3.2 U/mL may be considered an indicator of the onset of subclinical mastitis. Results of this study suggest that the fluorometric method may be applied in a manual test for subclinical mastitis. (Abstract shortened by UMI.).