PSXIV-29 Differential placental gene expression in response to winter feeding high-forage and high-concentrate diets in beef cows.

Abstract The objective of this study was to determine the effects of high forage (2.02 Mcal/kg dietary ME) or high concentrate (2.84 Mcal/kg dietary ME) diets on the differential gene expression and underlying biological pathways in cotyledonary placental tissue of beef cows. Forty-six pregnant (210 ± 10 d of gestation) Angus and Simmental-Angus cows (BW = 630 ± 12.0 kg) were blocked by breed, age, and body weight (BW) and assigned to one of two treatments: 1) Ad-libitum feeding of a forage-based diet (HFOR; n = 23); or 2) a corn-based diet limit-fed at 1.2% BW (HCON; n = 23). Cows were housed in a group-pen at the SDSU Cow-Calf Research Facility (Brookings, SD). Treatments were applied on d 50 (± 10 d) pre-calving and continued until d 84 post-calving. Calving was observed for each cow, and placentas were collected immediately following natural expulsion. The largest cotyledon closest to the umbilicus was dissected and rinsed with phosphate-buffered saline solution. A 2.5 ´ 2.5 cm2 of cotyledonary tissue (n = 10 per treatment) was snap-frozen in liquid nitrogen and stored at -80°C. Total RNA was isolated from the samples and subjected to RNA sequencing (HCON = 7 and HFOR = 6). After quality control, the reads were mapped to the Bos taurus reference genome using STAR aligner, and differentially expressed genes (DEGs) were identified using DESeq2. Transcriptomics analysis revealed 460 DEGs between the groups (P ≤ 0.05 and |Log2FC| > 1). Among them, 182 genes were upregulated, and 278 were downregulated in the placenta of HFOR cows. Nutrient transporter genes (SLC4A3, SLC28A3, and SLC25A16) were among the upregulated genes in the HFOR group. Functional over-representation analysis of DEGs through ShinyGO retrieved biological processes (BP) and KEGG pathways. Significant BPs included genes involved with angiogenesis and circulatory system development. Mitochondrial genes (MT-ND2, MT-CO2, MT-ATP6, MT-ND4L, MT-ND4, MT-ND6, andMT-CYB) were upregulated in the placenta from HFOR cows and over-represented in the oxidative phosphorylation pathway. Similarly, histone protein-coding genes were upregulated (H2AC18, H2AC20, H2AC10, and H2BC19), suggesting chromatin remodeling events linked to the regulation of placental gene expression. Differences in maternal diet during gestation affected the transcriptomic profile of cotyledonary placental tissue in beef cows. These transcriptomic changes may reflect underlying mechanisms through which maternal nutrition influences placental function and, ultimately, fetal development and offspring performance. However, further studies are required to explore the long-term implications of these alterations on animal performance.