Histological response of the bovine mammary gland to intramammary devices.

Histologic response of the bovine mammary gland to presence of three intramammary device models (abraded, star, or grooved) was studied in 12 lactating cows. Uninfected quarters fitted with devices exhibited greater leukocyte infiltration into teat and gland cistem linings as well as into mammary parenchyma adjacent to the gland cistem compared with unfitted control quarters. Cytologic alterations to cistem linings in device-fitted quarters ranged from degeneration and sloughing of surface cells of the double-layered epithelium to hyperplasia, stratification, and keratin formation. In uninfected quarters, quantification of mammary parenchymal components showed no differences among models for percentages of epithelium, but percentage of lumen was lowest and stroma highest for the star intramammary device model, suggesting reduced secretory activity or mammary involution in response to these intramammary devices. Presence of bacterial infection amplified the histologic responses to all devices. Leukocyte infiltration remained greater in device-fitted quarters compared with controls but was elevated over uninfected quarters for all treatments. Likewise, hyperplasia, stratification, and keratin formation of the cistem epithelial lining were more frequently observed in infected quarters. Among models in infected quarters, percentage of lumen was lowest and stroma highest in quarters fitted with abraded devices. In most cases, presence of infection masked any effect of devices on mammary parenchymal components. Plaque formation was observed on all models and tended to be thicker on those retrieved from infected quarters. Electron microscopic examination showed that plaque was composed of leukocytes, cell debris, keratin, and amorphous material. Results demonstrated that most intramammary device models were successful in stimulating leukocytosis into the gland, and tissues from fitted quarters displayed alterations to cisternal linings; however, quarters fitted with these devices exhibited reduced secretory activity.