RNA-seq analysis of mammary transcriptome in lactating dairy cows as affected by oral sodium salicylate

Previous studies have demonstrated non-steroidal anti-inflammatory drug (NSAID) treatment in early lactation had a positive impact on whole-lactation milk production in older cows. The objective of this study was to evaluate transcriptional changes in the mammary gland that could explain increased production responses due to NSAID treatment. Sodium salicylate (SAL; 125 g/d) or water (CON) were administered via oral drench to multiparous cows (n = 8/treatment) once daily for 3 d beginning approximately 24 h after parturition, and mammary tissue was collected on d 1, 4, and 45 postpartum. Day 1 tissue was collected immediately preceding the initial drench, and d 4 tissue was collected 24 h following the final drench. Cows were milked twice daily until d 7 of lactation, and thrice daily for the remainder of the study. Total RNA extracted from tissue was deep-sequenced and analyzed for differential gene expression using DESeq2. We detected no treatment effect on milk yield or plasma metabolites through 45 d of lactation. Comparison of SAL vs. CON revealed that only 16 of 18,286 genes were differentially expressed (false discovery rate < 0.1) in mammary tissue collected on d 45, while no differentially expressed genes due to treatment were detected on d 1 or d 4. Analysis of transcriptional differences over time showed downregulation of pathways related to immune cell recruitment and differentiation, and extensive overlap with pathways related to cholesterol synthesis and liver X receptor signaling.