Nitrogen (N) is a pivotal element that drives plant growth, yet it is the most limiting nutrient for pasture production (Mills, Moot, & Jamieson, 2009). In particular, dryland pasture soils in arid and temperate regions are often low in N. Therefore, increasing N availability in dryland pastures that are managed under low-input production systems is a primary need to improve productivity. Application of chemical fertilizers can be costly and challenging, particularly in difficult terrains such as hill and high-country pastures. In such environments, biological N 2 fixation by legumes, through their symbiotic relationship with soil bacteria, is an excellent tool to increase N availability for pasture plants (Ledgard & Steele, 1992). Nitrogen recycled through the grazed grass-legume pasture systems improves forage quality. Additionally, a higher legume content of pastures leads to higher herbage intake and productivity of grazing livestock

Selenium (Se) is an essential micronutrient for growth and immune function in beef cattle. We previously showed that supranutritional maternal organic Se supplementation during late pregnancy improves immune function in their newborn calves; however, the effects of maternal organic Se-supplementation on fetal programming during different pregnancy stages have yet to be elucidated. Herein, we investigated the effects of supranutritional maternal organic Se-supplementation in different pregnancy trimesters on their beef calf’s genome-wide transcriptome profiles. Within 12 to 48 h of birth, whole blood and Longissimus dorsi (LD) muscle biopsies were collected from calves born to 40 crossbred Angus cows that received, except for the control group (CTR), Se-yeast boluses (105 mg of Se/wk) during the first (TR1), second (TR2), or third (TR3) trimester of gestation. Whole-blood Se concentrations of newborn calves increased from CTR, TR1, TR2 to TR3, whereas muscle Se concentrations of newborn calves were only increased in TR3 group. We identified 3048 unique differentially expressed genes (DEGs) across all group comparisons (FDR ≤ 0.05 and |log2FC| ≥ 1.5). Furthermore, we predicted 237 unique transcription factors that putatively regulate the DEGs. Independent of supplementation trimester, supranutritional maternal organic Se supplementation downregulated genes involved in adaptive immunity in all trimesters. Dependent on supplementation trimester, genes involved in muscle development were upregulated by TR3 Se supplementation and downregulated by TR1 Se-supplementation, and genes involved in collagen formation were downregulated by TR2 Se-supplementation. Supranutritional maternal organic Se supplementation in the last trimester of pregnancy resulted in upregulation of myosin and actin filament associated genes, potentially allowing for optimal muscle function and contraction. Our findings suggest a beneficial effect of supranutritional maternal organic Se supplementation during late gestation on Se-status and muscle development and function of newborn calves.