Total and Differential Somatic Cell Counts and N-Acetyl-ß-D-glucosaminidase Activity in Mammary Secretions During Dry Period

¹ USDA, ARS, Beltsville, MD and University of Maryland, College Park 20742

Eighteen Holstein cows free of intramammary infection were sampled during dry period to measure changes in total SCC, differential cell counts, and N-acetyl-ß-D-glucosaminidase activity of milk or dry secretion. The design was to sample prior to and at drying off, two or more times during wk 1 of dry period, at 14 and 21 d of dry period, and after calving; 7 cows were sampled rotationally by quarters at 7, 14, and 21 d to avoid altering normal processes by repeated sampling. Total SCC of secretions declined just after drying off, increased to a peak of 6.593 (log₁₀ scale) at 2 wk, and then declined slightly at 3 wk. Percentage of neutrophils rose from 33.3 at drying off to 83.8 at 1 wk and declined to 59.2 at 3 wk. Lymphocyte percentage declined in wk 1 of dry period but increased during wk 2 and 3. Activity of N-acetyl-ß-D-glucosaminidase in secretion rose throughout the first 3 wk of dry period.

Key Words: mastitis • cell defenses • infection

Submitted on October 30, 1989
Accepted on February 5, 1990

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