Final answer:
Mastitis pathogens most commonly gain access to the mammary gland through direct contact via the teat canal, as this is a natural opening that can be contaminated by the environment or during the milking process.
Step-by-step explanation:
The question on how mastitis pathogens most commonly get into the mammary gland has to do with the infection routes into the mammary tissues. Despite bacteria being able to enter the circulatory and lymphatic systems through various means like wounds or medical procedures, mastitis is most often caused by direct contact through the teat canal. This is because the teat canal serves as a natural opening through which bacteria from the environment, particularly the surface of the skin and bedding material, can enter the gland and cause infection. It is less common for mastitis pathogens to enter through the bloodstream or lymphatic system, as these would typically be indicative of a more systemic infection.
Mastitis being an infection of the mammary gland is thus primarily associated with factors such as poor milking hygiene, damage to the teat skin, teat injuries, or a compromised immune system which can all facilitate the entry of pathogens through the teat canal.