Udder swelling occurs when the mammary glands become inflamed due to infection, trauma, or other factors. The most common cause is bacterial infection, with pathogens such as *Staphylococcus aureus* and *Escherichia coli* being the primary culprits. Milking machine malfunctions, improper milking techniques, and poor hygiene practices can also exacerbate the risk of infection. Environmental stressors, nutritional deficiencies, and systemic diseases can further contribute to the swelling.
