Technical Abstract: The objective of this study was to evaluate synchronization and pregnancy rates of beef heifers supplemented with 0.91 kg of whole sunflower seeds for either 0, 30, or 60 d before AI. Beef heifers from four locations (n = 1,014) were assigned by body weight (BW) to treatment (within location) and randomly to AI sire. Heifers at Location 1 (n = 176; mean BW = 332 kg) received either 0 or 60 d treatments. Heifers at Location 2 (n = 397; mean BW = 334 kg) were fed sunflower seeds for 0, 30, or 60 d. Heifers at Locations 3 (n = 211; mean BW = 345 kg) and 4 (n = 230; mean BW = 343 kg) received 0 or 30 d treatments. Within location, diets were formulated to be isocaloric and isonitrogenous. All heifers received melengesterol acetate (0.5 mg/hd/d) for 14 d followed 19 d later by an injection of PGF (25 mg). Heifers were bred by AI according to the AM/PM rule except on d 3 during which all heifers which had not exhibited estrus were mass AI. Neither 72 h estrous response nor pregnancy rate were affected (P>0.10) by 30 or 60 d sunflower feeding. Neither estrous response nor pregnancy rate was affected (P>0.10) by treatment. In summary, feeding 0.91 kg of whole sunflower seeds for either 30 or 60 d before AI did not improve estrous response or pregnancy rate compared to controls.