The impact of feeding flax as seed, meal, or oil to late-pregnant and lactating sows on hormone concentrations, immune responses, and sow and litter performances was studied. Sixty sows were fed 1 of 4 diets from 68 d of gestation until 21 d of lactation. Diets were standard (CTL; n = 15); 10% flaxseed supplementation (FS; n = 16); 6.5% flaxseed meal supplementation (FSM; n = 14); and 3.5% flaxseed oil supplementation (FSO, n = 15). On d 88 and 101 of gestation, sows were immunized against ovalbumin (OVA). Jugular blood samples were obtained on d 62, 88, and 110 of gestation and on d 2 and 21 of lactation to measure concentrations of estradiol, prolactin, and progesterone as well as antibody (Ab) against OVA (anti-OVA), lymphocyte proliferation, and lymphocyte production of interferon-γ (IFN-γ). Milk samples were obtained on d 3 and 20 of lactation. One piglet per litter was slaughtered on d 1 for compositional analyses, and a jugular blood sample was obtained for anti-OVA analyses. Remaining piglets were weighed on d 2, 7, 14, 21 (weaning), 28, and 56. Circulating hormone concentrations in sows were not affected by treatment overall. On d 20 of lactation, milk from FS, FSM, and FSO sows had more protein than that from CTL sows. The FSM piglets weighed more on d 56 than FS and FSO piglets. Carcasses of 1-d-old FSM piglets also had greater glycogen and DM contents than FS and FSO piglets, but organ weights and circulating concentrations of glucose and IGF-I did not differ. In CTL sows, IFN-γ production decreased between d 101 of gestation and d 2 of lactation, whereas, in FS sows, IFN-γ production increased. Anti-OVA for the whole experimental period was greater in FS than in FSO sows. Concentrations of anti-OVA in milk on d 3 of lactation and lymphocyte proliferative responses were not affected by treatments. Serum concentrations of anti-OVA in 2-d-old piglets that gained BW during the first 24 h after birth were greater in FS, FSM, and FSO litters than in CTL litters and percent mortality on d 2 and 21 postpartum was less for FS, FSM, and FSO litters compared with CTL. Therefore, feeding flax to sows may have beneficial effects on immune resistance of piglets and feeding FSM improved postweaning growth of piglets. 

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