The dry period in cow are critical to mammary health and the success of the next lactation. The expression of proteins the dry period progresses need to be characterized to provide information on involution and immune functions during the dry period. Total protein and lactoferrin concentrations rose significantly by days 10 and 21 after cessation of lactation. Using the day 21 dry secretions we examined their ability to inhibit bacterial growth. Bacterial growth inhibition was not correlated with lactoferrin for 4 coliforms tested nor for all 7 mastitis pathogens. Label free mass spectroscopy was used to quantify changes in whey proteins from milk/dry secretions collected on days 0, 3,10, and 21 of the dry period. 776 proteins were identified. 109 proteins were upregulated at one or more times in the dry period. The most significate enriched GO functional terms for the up-regulated proteins were immune function and stress related. 68 proteins were down regulated in the dry period. The most significant enriched GO functional terms for the down-regulated proteins were stress and immune function related. 12 proteins were significantly correlated with coliform growth. The dry secretion composition changes we found provide information for understanding the dry period.