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Effects of Parity, Bacteriological Status, Stage of Lactation, and Dry Period on N-Acetyl-ß-D-Glucosaminidase Activity of Milk and Dry Secretion

US Department of Agriculture, Agricultural Research Service, Milk Secretion and Mastitis Laboratory, Beltsville, MD 20705

ABSTRACT

Quarter foremilk samples from 61 cows were obtained at 1.5, 3, 21, and 35 wk of lactation and at 7 d after drying off. Measurements for each sample were milk SCC, NAGase activity in the milk and ability of milk to promote phagocytosis of Staphylococcus aureus by polymorphonuclear leukocytes. Milk SCC and NAGase were correlated (r = .62). The NAGase in dry cow secretion was 10-fold higher than in milk. Parity differences in NAGase activity were not significant. There were large stage of lactation trends in NAGase: NAGase activity was high in early lactation, decreased in midlactation, and increased in late lactation and in dry secretion. The increase in activity of the enzyme in milk of first parity cows in late lactation was not as great as in milk of second and third lactation cows. N-Acetyl-ß-D-glucosaminidase activity of milk from quarters with intramammary infections was higher than that of milk from quarters free of pathogens.

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