Linoleic and linolenic acids are involved in both implantation and central nervous system development of the embryos. By supplementing gestation diets with these essential fatty acids (FAs), it may be possible to enhance embryo survival, litter size and piglet survivability. Approximately 60 sows and gilts were used for each of 3 trials. Animals were housed on straw in groups of 14 to 16 and were fed once daily in individual feeding stalls. On day of breeding (d0) animals were randomly assigned within pen to 1 of 3 treatments; diet 1 (T1) - control (commercial dry sow), diet 2 (T2) - starch (equal energy intake to diet 3, but no supplemental fatty acids), diet 3 (T3) - oil (supplemented with flax seed oil to bring linoleic acid content to 2%). Animals were formula-fed according to body weight (BW) during gestation (1%BW + 0.7kg). The test diets were fed until day 40 of gestation, after which all animals returned to the commercial gestation ration (control). In trial 1, the younger growing animals were weaned in relatively poor body condition and older mature animals tended to be over-conditioned. For trials 2 and 3, the feeding formula was adjusted to account for body condition as well as body weight. (Abstract shortened by UMI.)