Morphological characteristics of somatic cells from mammary glands of unbred heifers

Juvenile mammary glands of unbred heifers were chosen as the object for studies of resistance of the bovine mammary gland to infection. The purpose of this work was to recognise the functional state of juvenile mammary glands of unbred heifers as reflected in absolute and differential counts and morphology of somatic cells. The results of determination of absolute and differential somatic cell counts of noninfected nonsecreting and noninfected aberrantly secreting mammary glands of unbred heifers, incl. morphologic cell characteristics are presented. The whole set included 160 mammary glands of which 135 (84.4%) were noninfected and nonsecreting, 7 (4.4%) noninfected and aberrantly secreting, and 18 (11.2%) infected. Absolute counts of somatic cells in lavages standardised on a constant volume (20 ml) were (0.985 +/- 0.882). 10(6)/ml and (2.713 +/- 1.514). 10(6)/ml for the noninfected nonsecreting and the aberrantly secreting glands, respectively. The difference was significant at P < 0.05. Macrophages of the nonvacuolised and vacuolized types predominated in the differential counts both in the nonsecreting (72%) and in the secreting (56.4%) glands. The vacuolized type represented degenerated macrophages and macrophages filled with fat globules in the nonsecreting and the aberrantly secreting glands, respectively. In addition to the typical polymorphonuclear leukocytes, cells showing a certain degree of degeneration were observed. Functional alterations in aberrantly secreting mammary glands were reflected in a marked increase in absolute somatic cell counts, in an increase of the proportion of polymorphonuclear leukocytes in differential cell counts, and a decrease in the proportion of lysed cells. Characteristics of absolute and differential somatic cell counts will be analysed as potential markers of resistance of the mammary gland to infection.