Although dietary content of tryptophan has been related to variations of feed intake in lactating sows, the mechanisms remain to be elucidated. Twenty multiparous crossbred Landrace times Large White sows were used to assess variations of tryptophan metabolism around farrowing. Sows were fed 3 kg/d of a standard gestation diet from insemination until farrowing. They were then fed ad libitum a standard lactation diet until weaning. Sows were catheterised on day 70 of gestation and blood samples were drawn on day 37 before parturition, daily during the week before and the week after farrowing, and on days 14 and 21 of lactation. Plasma concentrations of amino acids, kynurenine, niacin, haptoglobin, urea, and vitamin B6 concentration in red blood cells were determined. During the week following parturition, plasma tryptophan and niacin decreased while plasma kynurenine increased (p < 0.05). On the 2nd and 3rd weeks of lactation, plasma tryptophan and kynurenine returned to pre-farrowing concentrations, while niacin increased throughout lactation (p < 0.05). Vitamin B6 increased progressively during the week after farrowing (p < 0.05) and remained constant at a high concentration thereafter. The average feed intake of the sow during lactation was positively correlated with the mean concentrations of niacin (r2 = 0.25; p < 0.001) and kynurenine (r2 = 0.31; p < 0.001) in plasma and with vitamin B6 in red blood cells (r2 = 0.68; p < 0.001). This study suggests that tryptophan catabolism presumably through the kynurenine pathway is high during the 1st week after farrowing, and that dietary supply of niacin and vitamin B6 could be transiently suboptimal in early lactation.