MicroRNA profiles of dry secretions through the first three weeks of the dry period from Holstein cows

Authors: PUTZ, ELLIS - Iowa State University; PUTZ, AUSTIN - Iowa State University; JEON, HYEONGSEON - Iowa State University; Lippolis, John; Ma, Hao; Reinhardt, Timothy; Casas, Eduardo

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2019
Publication Date: 12/23/2019
Citation: Putz, E.J., Putz, A.M., Jeon, H., Lippolis, J.D., Ma, H., Reinhardt, T.A., Casas, E. 2019. MicroRNA profiles of dry secretions through the first three weeks of the dry period from Holstein cows. Scientific Reports. 9(19658). https://doi.org/10.1038/s41598-019-56193-5.
DOI: https://doi.org/10.1038/s41598-019-56193-5

Interpretive Summary: For dairy cattle, there are vast biological and physiological changes as the cow goes through various stages of lactation. The ‘dry period’ where the cow does not produce milk before she calves again and begins another lactation is an important time for repair and cell turnover in the mammary gland. The health of the mammary gland during the dry period can have an immense impact on disease susceptibility and milk production during the subsequent lactation. MicroRNAs (miRNAs) are small RNAs that can regulate gene expression. This paper explores the miRNA profile from dry secretion samples of six Holsteins from their last day of lactation, through the first three weeks of the dry off period. MiRNAs that are upregulated or downregulated are insightful into the biological processes the mammary gland is undergoing. In addition to increasing our general knowledge of mammary gland biology, have the potential to identify candidate proteins or pathways to target with the development of disease preventative therapeutics, or contribute better dairy cow health practices. We used traditional statistical modeling to evaluate changing expression of miRNAs, but we also cross-analyzed our data using a unique slope based approach looking at miRNA counts over time. Over the 398 miRNAs that met our criteria to be analyzed, we found 46 miRNAs that significantly changed during the first three weeks of the dry period (including both miRNAs that were upregulated and downregulated). Of those significantly expressed miRNAs we found meaningful references of these miRNAs associated with important dairy cow parameters such as lactation, disease and inflammation, and pregnancy and reproduction. These results establish that dry secretions are a valuable sample for studying miRNAs in dairy cow and add contribute to our knowledge and biological characterization of the dry period.

Technical Abstract: In dairy cows, the period from the end of lactation through the dry period and into the transition period, requires vast physiological and immunological changes that are key to mammary health. The mammary gland experiences cellular turnover and repair during dry period. The dry period is, in many ways, key to the success of the next lactation and intramammary infections during the dry period will adversely alter mammary function, health and milk production for the subsequent lactation. MicroRNAs (miRNAs) are small non-coding RNAs that have been shown to post transcriptionally regulate the expression of genes. In this study, we sought to characterize the miRNA profile in dry secretions from the last day of lactation to 3, 10, and 21 days post dry-off. We identified 816 miRNAs known miRNAs and 80 novel miRNAs. There were 398 miRNAs were used for expression analysis that had a minimum of 10 counts in at least four cows on at least one experimental day. We found 46 miRNAs whose expression significantly changed (q-value less than 0.05) over the first three weeks of dry-off. In an additional analysis, we examined the slopes of random regression models of log transformed normalized counts and cross analyzed the 46 significantly upregulated and downregulated miRNAs . These miRNAs were found to be associated with important components of pregnancy, lactation, as well as inflammation and disease. Detailing the miRNA profile of dry secretions through the dry-off period provides insight into the biology at work, possible means of regulation, components of resistance and/or susceptibility, and outlets for targeted therapy development.