Maternal supplementation with omega-3 fatty acids during late gestation has been shown to have a variety of benefits for neonates. The current study utilized 13 mares and their foals, assigned to one of three dietary treatments: an unsupplemented control diet (CON; n = 5), or the addition of either fish oil-derived omega-3 (FO; n = 5) or a flaxseed (FLAX; n = 3) supplement. The mares received treatments beginning on day 310 of gestation through day 5 post-parturition. Samples of plasma were collected from the mares prior to beginning supplementation, on days 0, 5, and 30 post-partum. Milk samples were collected from the mares 12 h post-partum. Plasma samples were collected from the foals at birth and at 5 and 30 d post-partum. The fatty acid compositions of the mare plasma, mare milk, and foal plasma were determined using gas chromatography. The data were analyzed using repeated-measures ANOVA. Foals born to FO mares exhibited increased plasma docosahexaenoic acid (DHA) levels at birth compared with those born to CON mares. Across the treatments, the plasma from foals at birth prior to nursing had the highest DHA content compared with on d 5 and 30. No treatment differences were observed in the mare plasma or milk fatty acid composition for DHA levels. FLAX mares had higher 20:3 n6 plasma proportions than FO or CON mares. Beginning supplementation with fish oil on day 310 of gestation may be sufficient to elevate neonatal foal DHA concentrations.