LAUSR

Our objectives were to determine the effects of feeding vitamin and mineral (VTM) and (or) energy (NRG) supplements to beef heifers during the first 83 days of gestation on concentrations of progesterone (P4), corpus luteum (CL) size, and fetal body measurements. Crossbred beef heifers (n = 35; initial BW = 359.5 ± 7.1 kg) were blocked by weight and assigned to one of four treatments (n = 8 or 9/group) in a 2 × 2 factorial arrangement with main effects of vitamin and mineral (NoVTM or VTM) and energy (NoNRG or NRG) supplements. A basal total mixed ration was fed once daily with VTM and NRG top-dressed. The VTM treatment (113 g•heifer-1•d-1) was initiated 71 to 148 d before AI. At AI, heifers were bred to a single sire, and NRG was initiated with target gains of 0.28 kg/d for NoNRG and 0.79 kg/d for NRG. Serum was collected on d 14, 28, 42, 56, 70, and 83 after AI and analyzed for. Gravid reproductive tracts were collected by ovariohysterectomy on d 83 ± 0.27 of gestation, and fetuses were dissected. An NRG × day interaction (P = 0.006) was observed for P4, with concentrations similar on d 14 to 56, a tendency (P = 0.09) for divergence at d 70, and greater (P = 0.002) concentrations for NRG on d 83 compared with NoNRG heifers. Furthermore, NRG heifers had greater CL weights than NoNRG (P = 0.003). Fetuses from NRG dams had greater (P = 0.009) femur weights than fetuses from NoNRG. Fetal liver weight was greater (P = 0.05) from dams fed VTM than NoVTM. Overall, providing NRG supplements during early gestation resulted in heavier CLs, that produced more P4, and greater fetal femur growth, whereas providing VTM supplements enhanced fetal liver growth.