Characterization of bovine mammary gland dry secretions and their proteome from the end of lactation through day 21 of the dry period.

The dry period in dairy cows is critical to mammary health. We used label-free mass spectroscopy to quantify whey proteins from milk/dry secretions collected on days 0, 3,10, and 21 of the dry period. The number of proteins identified was 776. The number of proteins upregulated at one or more times in the dry period was 109. The most significant enriched Gene Ontology (GO) terms for the upregulated proteins were immune function and stress-related. The number of proteins that are downregulated in the dry period was 68. The most significant enriched GO terms for the down-regulated proteins were stress and immune function related. In other assays, total protein and lactoferrin concentrations rose significantly by days 10 and 21 of the dry period. We then examined day 21 dry secretions for their ability to inhibit bacterial growth. Bacterial growth inhibition did not correlate with lactoferrin for 4 coliforms tested nor for all 7 mastitis pathogens tested. Eleven proteins out of the total number of proteins identified were significantly associated with positive or negative coliform growth in day 21 dry secretions. The dry secretion protein composition changes we found may provide new information for understanding the dry period and indirectly involution.