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 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 (0.5mg/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'd. Data were combined for locations 1 and 2 to test the effect of 0 and 60 d sunflower feeding. Data from locations 2, 3, and 4 were combined to test the effect of 0 and 30 d sunflower feeding. Heifers fed the control diet had a higher (P < 0.01) ADG than heifers fed sunflower seeds for 60 d. There was a location x treatment interaction (P < 0.01) for ADG in the comparison of 30 and 0 d sunflower treatments. Neither 72 h estrous response nor pregnancy rate were affected (P > 0.10) by 30 or 60 d sunflower feeding. Pregnancy rate for heifers detected in estrus was 68% and 33% for mass bred heifers, estrous response by 72 h was 71%. 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.