Significance
The dry period in a cow is critical to the success of a cow's subsequent lactation for many reasons. Of particular importance is the rate of establishment of new intramammary infections (IMI), which is significant in the dry period. IMI susceptibility is most significant in the first few weeks of the dry period. There are both physical and mechanical reasons for increased IMI susceptibility in the first few weeks of the dry period. We also know that dry secretions have high levels of antimicrobial proteins and bacterial growth is diminished in dry secretions compared to milk. However, we found that by day 21 of the dry period, antimicrobial proteins, such as lactoferrin, are no longer correlated with reduced bacterial growth in dry secretions. We established a dry secretion proteome for the first 3 weeks of the dry period. The library of proteins in dry secretions presented provides a better understanding of the critical dry period in dairy cow management.