We studied the effect of conjugated linoleic acid (CLA) on rat development and growth. Primigravid female Fischer rats were fed control or CLA-supplemented (0.25% or 0.5% CLA) diets during gestation and/or lactation. Conjugated linoleic acid was incorporated into milk fat and tissue lipids proportional to the level of CLA fed and the duration of CLA feeding. Conjugated linoleic acid was incorporated into fetal and neonatal tissues; it did not affect litter size nor induce apparent abnormalities. To the contrary, feeding CLA to the dams during gestation and lactation improved the postnatal body weight gain of pups (P < 0.05), measured on d 10 of lactation. Pups that continued to receive the CLA-supplemented diet after weaning had significantly greater body weight gain and improved feed efficiency relative to control animals (P < 0.05).