Effects of intramammary infection and parenchymal region on collagen abundance in nonlactating bovine mammary glands

Objective The objectives were to quantify collagen content in nonlactating uninfected and Staphylococcus aureus–infected mammary glands and determine the relative abundance of collagen in different gland regions. Materials and Methods Mammary tissues that were previously collected from a mastitis-challenge trial were examined. Mammary tissues were collected along a vertical midline through each gland and included parenchymal tissues that were proximal to the gland cistern (cisternal parenchyma) and tissues near the abdominal wall (deep parenchyma) from each saline-infused (n = 18) and Staph. aureus–infused (n = 18) gland. Collagen was detected via picro-sirus red staining and visualized using polarized light for image acquisition and subsequent analysis. Results and Discussion Most interlobular collagen was associated with larger ducts and stromal tissues. Some collagen was intralobular and was mostly associated with these larger ducts but was also present in epithelial basement membranes. Staphylococcus aureus–infused glands contained more tissue area occupied by collagen than saline-infused glands (19.78 vs. 17.26 ± 1.19%). Additionally, parenchyma near the gland cistern contained more collagen than deep parenchyma (19.95 vs. 17.09 ± 1.19%). Results indicate that mastitis elicits the deposition of collagen in affected glands and that collagen abundance is affected by gland region. Implications and Applications Nonlactating mammary glands affected by Staph. aureus mastitis may have a greater amount of collagen, believed to be resulting scar tissue. We speculate that it may have long-term, and possibly irreversible, effects on glandular structure and, consequently, lifetime productivity.