From the NMC Newsletter "Udder Topics", June-July 2002
Several risk factors contribute to the variation in susceptibility to new intramammary infection during the dry period. These factors include:
Bacterial populations on the teat end:
The cessation of milking hygiene practices, such as teat dipping, allows bacterial populations on teat skin to increase. Staphylococcus aureus and environmental Streptococci bacterial numbers on teat skin are high immediately after drying-off. Coliform organisms are more prevalent on teat skin late in the dry period and at calving time.
Variations in the teat streak canal:
Studies suggest that the teat canal is more easily penetrated by bacteria during the early dry period. Similarly, swelling of the mammary gland, the increasing volume of secretion, and the leaking of colostrum, contribute to the high risk of new infection during the prepartum period.
Resistance mechanisms within the mammary gland:
Throughout the dry period, there are marked changes in the composition of mammary gland secretions. There is an increase in the concentration of protective factors such as leucocytes, immunoglobulins, and lactoferrin. These changes influence the variation in susceptibility to both environmental and contagious pathogens. When the gland is completely involuted, resistance to new intramammary infections is high.
Source: National Mastitis Council Regional Meeting Proceedings (1999) pg. 35