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Variation in N-Acetyl-ß-D-Glucosaminidase Activity and Somatic Cell Count Among Various Milk Fractions¹

Department of Animal Sciences, University of Maryland, College Park 20742

ABSTRACT

Six Holstein cows with uninfected quarters were quarter machine milked for four consecutive morning milkings. Foremilk, bucket, and stripping fractions were collected for all milkings. For the first three milkings, an additional milk sample was collected 1 h after milking. After the final milking, oxytocin (20 IU) was injected in the tail vein 20 min after milking, and residual milk was collected. All samples were assayed for NAGase activity and somatic cell concentration. Mean NAGase activity for foremilk, bucket, and stripping samples were 1.65, 1.55, and 1.84 log_e nmol/min/ml. Hour after milking and residual samples averaged 2.07 and 1.78. Cell counts (log_e thousand cells/ml) for foremilk, bucket, and strippings averaged 2.52, 2.91, and 4.30. Hour after and residual samples averaged 4.56 and 5.53. Results suggest that among uninfected cows, foremilk approximates bucket levels of NAGase and cell count.

¹ Scientific Article Number A-4543, Contribution Number 7537 of the Maryland Agricultural Experiment Station, Department of Animal Sciences.

² Milk Secretion and Mastitis Laboratory, USDA-ARS, Beltsville, MD.