Submitted to: Journal of Proteomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2020
Publication Date: 5/18/2020
Citation: Reinhardt, T.A., Lippolis, J.D. 2020. Characterization of bovine mammary gland dry secretions and their proteome from the end of lactation through day 21 of the dry period. Journal of Proteomics. https://doi.org/10.1016/j.jprot.2020.103831.
Interpretive Summary: The dry period is critical to the success of the subsequent lactation for many reasons. Of particular importance is the rate of establishment of new mastitis infection is greater in the dry period than in lactation. Mastitis susceptibility is greatest in the first few weeks of the dry period. Though there are both physical and mechanical reasons for increased Mastitis susceptibility in the first few weeks of the dry period, we know from the work of others 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 proteins such as lactoferrin no longer correlated with reduced bacterial growth in dry secretions. The establishment of a dry secretion proteome for the first 3 weeks of the dry period is the start of a library of information to better understand this critical period in dairy cow management.
Technical Abstract: The dry period and concomitant mammary involution in dairy cattle are critical to mammary health and the success of the next lactation. The changes in the expression of proteins as mammary involution and the dry period progresses need to be characterized to provide information on both the process of involution and dry period immune functions important during the dry period. Consistent with the literature both 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 using 7 mastitis pathogens. Interestingly bacterial growth inhibition was not correlated with lactoferrin concentration for 4 coliforms tested nor for all 7 mastitis pathogens in day 21 dry secretions. Significant cow to cow variation was seen in the ability of day 21 dry secretion to inhibit of bacterial growth. 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 with a false discovery rate of 0.1 %. 109 proteins were upregulated at one or more of the sample times in the dry period. The most significant enriched GO and Reactome functional terms for the up-regulated proteins were immune function and stress related. 68 proteins were down regulated at one or more times in the dry period. The most significant enriched GO and Reactome functional terms for the down-regulated proteins were stress and immune function related. We found evidence that the expression of 12 proteins were significantly correlated with coliform growth in day 21 dry secretions. The dry secretion protein composition changes we found do provide new information important for understanding the first 3 weeks of the dry period and mammary involution.