Bovine milk N-acetyl-β-D-glucosaminidase and its significance in the detection of abnormal udder secretions

Summary A new spectrofluorimetric assay procedure for bovine milk N-acetyl-β-D-glucosaminidase (NAGase) is described for use as a routine screening test for the detection of abnormal uddersecretions. This procedure uses 4-methylumbel-liferyl-N-acetyl-β-D-glucosaminide as substrate. On the basis of the greater sample throughput, increased product sensitivity detection of NAGase and the absence of turbidity problems, it is considered to be superior to a previously reported spectrophotometric procedure (Kitchen, 1976). The correlation coefficient between the somatic cell count and the fluorimetric procedure using 243 quarter fore-milk samples was 0·86. Distribution studies on bovine milk and mammary gland homogenates indicated that this enzyme activity was located predominantly in the soluble whey protein fraction and the post-microsomal supernatant. Mammary gland secretory cells contained high levels of NAGase and appeared to be the major source of the enzyme in milk whilst NAGase from other sources (white blood cells, blood serum) contributed only a minor proportion (5–15%) of the total activity in milk. The implications of these findings on the value of the NAGase test as a means of mastitis diagnosis are discussed.