The mammary gland has various defense mechanisms that protect it from infections, ensuring the production of safe and clean milk. These defense mechanisms can be categorized into anatomical, cellular, and humoral factors. Anatomical defenses include the streak canal, keratin plug, teat orifice, teat sphincter, and Fürstenberg rosette, which all help prevent pathogen entry. Cellular defense is provided by leukocytes (polymorphonuclear neutrophils, macrophages, lymphocytes) and mammary epithelial cells. Leukocytes can be either resident (macrophages) or recruited from the bloodstream (PMNs, lymphocytes) through chemoattractant factors released by pathogens. Several humoral factors, including immunoglobulins, complement proteins, lactoferrin, transferrin, lysozymes, cytokines, and chemokines, are produced locally or transported from the blood, providing immune surveillance. These defense factors work together to maintain optimum udder health. There are various tools available to modulate the immune response in the mammary gland as preventive measures, such as genetic selection, micronutrient supplementation, cytokine immunotherapy, genetic engineering, herbal therapy, intramammary probiotics, and vaccination. These methods can help reduce the need for unnecessary antibiotic use.