Pathomorphological changes in the mammary glands are usually caused by the interaction of macroorganism, microorganism and the environment. A very important processs during intramammary infection is the penetration of microorganisms in a tank papilla. In the mammary gland, there are several mechanisms to prevent penetration of bacteria into the mammary gland. The first line of defence against penetration of pathogens into the mammary gland is ductus papillaris. The interior of the ductus papillaris filled with similar wax, which contains long-chain fatty acids and basic proteins. It was found that these substances in vitro bactericidal effect and bacteriostatic toward specific mastitis pathogens. Previously it was thought that the musculus sphincter papillae most important obstacle to the penetration of microorganisms into the mammary gland. Research tasks are focused on monitoring the length of the ductus papillaris and its impact on the occurrence of pathomorphological changes in the parenchyma of the udder.