Eighty-six crossbred (Duroc x Yorkshire) gilts were used in two trials (50 gilts in Trial 1 and 36 gilts in Trial 2) for an assessment of the effect of supplemental dietary fat during early gestation on fetal survival, fetal development, and fatty acid concentration in gilt plasma and fetal head and body. Three diets contained 4% (w/w) added fat either as coconut, soybean, or fish (menhaden) oils. A fourth diet was used as a control. On d 37 to 45 postbreeding, gilts were slaughtered and numerous fetal and ovarian measurements made. Two sets of four randomly selected fetuses per gilt from Trial 1 were prepared. Blood samples from each gilt were obtained on the day of slaughter for determination of the plasma fatty acid profile. Across both trials, percentage fetal survival did not differ according to treatment, but in Trial 2 fetal survival was higher (P < .06) for gilts fed fish oil, compared with the controls. The fatty acid profile of plasma of gilts and the conceptus tissues were similar; both were influenced by the fatty acid concentration of the diets. The ratio of n-3/n-6 fatty acids was higher in conceptus tissue than in maternal plasma and the ratio was higher (P < .05) for the fish oil diet compared with the other diets. The relatively high concentration of omega-3 fatty acids in fetal tissues supports the hypothesis that omega-3 fatty acids play a role in the development of the pig conceptus and contributes to improve fetal survival. However, the high percentage fetal survival observed in all the treatments may have masked benefits of supplemental oil. / Master of Science