Scholljegerdes, E. J., Lekatz, L. A. and Vonnahme, K. A. 2011. Effects of short-term oilseed supplementation on reproductive performance in beef heifers. Can. J. Anim. Sci. 91: 221-229. The objective of this experiment was to evaluate the role of a short-term increase in linolenic acid around the timed artificial insemination (TAI) on plasma fatty acid concentrations, estrous behavior, and pregnancy. Therefore, 96 cross-bred heifers (Initial BW=394±18.1 kg) fed chopped grass hay were allotted to one of three dietary treatments: no supplement (CON); 1.8 kg head^-1 d^-1 (DM basis) of a soybean-based pellet (SOY) high in linoleic acid (C18:2n-6); or 1.5 kg head^-1 d^-1 (DM basis) of a flaxseed-based pellet (FLX) high in linolenic acid (C18:3n-3). On day -9, relative to TAI, supplementation began, and heifers received a controlled internal drug-releasing (CIDR) device and gonadotropin releasing hormone (GnRH; 100 µg). On day -2, CIDRs were removed and heifers received 25 mg prostaglandin F₂α (PGF₂α). Heifers were bred by TAI (day 0) 54 h after CIDR removal and received GnRH. Estrous behavior was monitored throughout the feeding period by radiotelemetry. Supplementation ended on day 18 relative to TAI. Plasma concentrations of C18:2n-6 were greater by day 0 and day 18 (P<0.001) above that of CON for both SOY and FLX with SOY being greater than (P<0.001) FLX. Likewise, C18:3n-3 was also greater for supplemented heifers by day 0 and day 18 (P<0.001). The number of heifers that did not respond to estrous synchronization was not affected by dietary treatment (P=0.61). Conception to AI was not affected by treatment (P=0.24). Overall pregnancy rates tended to be lower for FLX (P=0.08) than SOY. Conception to a TAI program was not enhanced when oilseeds were fed to beef heifers during estrous synchronization and continuing past day 18 relative to artificial insemination.