Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Quarter milk secretion samples and blood serum for compositional analysis were collected weekly from 29 cows beginning at drying off and continuing until 2 weeks postpartum. Quarter biopsies were taken from 5 additional animals at weekly intervals beginning at drying off through parturition. Histological and cytological parameters of tissues were correlated with biochemical characteristics of secretions. Increased tight junction permeability and decreased synthetic ability of secretory epithelium became evident by changes in mammary secretion composition and tissue morphology during the first 2 weeks of involution. Somatic cell counts, serum albumin, lactoferrin, immunoglobulin G, pH, total protein, and serum concentrations of $\alpha$-lactalbumin increased while fat, citrate, and the citrate to lactoferrin molar ratio decreased. Morphometric analysis of tissue demonstrated increases in stroma and nonactive secretory epithelium with decreases in epithelium, lumen, and fully active secretory epithelium during the first 2 weeks of involution. Decreases in organelles associated with milk synthesis and secretion were observed also. These biochemical and structural changes reversed beginning 2 weeks prepartum, and by parturition, cell function and structure were typical of lactating glands. Infected quarters had significantly higher somatic cell counts, pH, and percent polymorphonuclear leukocytes, but lower concentrations of lactoferrin and percent lymphocytes compared to uninfected quarters. Tissue from infected quarters also had less synthetic and secretory ability with higher percentages of stroma and nonactive cells, but lower percentages of lumen compared to uninfected quarters. Plasma cell populations in bovine mammary tissue increased gradually from drying off, reached peak concentrations 2 weeks prepartum, and dropped significantly during the last week of gestation. Immunoglobulins G$\sb1$ and G$\sb2$ were the most numerous isotypes followed by immunoglobulins A and M. Immunoglobulin M cells were more numerous in tissue infected with minor pathogens than uninfected quarters. Ultrastructural examination revealed rough endoplasmic reticulum cisternae engorged with flocculent material indicative of antibody synthesis. Exposure to minor bacterial pathogens apparently elicited an immune response in nonlactating mammary tissue. These data provide information concerning the quantitation and distribution of components involved in the mammary immune system which may be manipulated to enhance the natural defense mechanisms of the involuted bovine mammary gland.