Mature sows were evenly assigned to six dietary treatments, which differed only in the concentration of total (apparent ileal digestible, AID) tryptophan (Trp) amounting per kg feed to 1.2 g (0.8 g) to 4.2 g (3.8 g) in diets 1-6. For a total of 72 lactations (28 days) sows' feed intake was measured daily and body weight was measured on day 110 of pregnancy and on days 1 and 28 of lactation. Litter size was standardized to 10-12 piglets within 1 week after farrowing. The piglets were weighed at days 1, 21 and 28. Milk yield was recorded by the weigh-suckle-weigh method on days 20 and 21. Concentrations of milk fat and protein were measured in manually drawn samples (days 20 and 21) by infrared spectroscopy. Average daily feed intake of the sows was 3.4, 4.7, 4.7, 6.1, 5.1 and 4.7 kg (diets 1-6 respectively, p < 0.001). Body weight losses of the sows during lactation were 30.8, 16.9, 19.2, 9.5, 14.1 and 13.1 kg (diets 1-6 respectively, p < 0.05). Milk output in the average of days 20 and 21 was 6840, 8192, 8362, 9035, 8618 and 8140 g/day, respectively (p < 0.01). There were no differences in milk fat or protein contents. Daily weight gain of the piglets in the average of lactation was 157, 184, 184, 187, 185 and 177 g, respectively (p < 0.10). Based on the results of this study the estimated Trp requirement of lactating sows for optimal performance was calculated with 1.9 g AID Trp/kg in the lactation diet (according to 2.0 g true ileal digestible Trp and approximately 2.6 g Trp on total basis).

Mature sows were fed for a total of 72 lactations with diets which provided an adequate supply of energy and nutrients except for tryptophan (Trp). By supplementing a basal diet [native 1.2 g Trp/kg, equivalent to 0.8 g apparent ileal digestible (AID) Trp or 0.9 g true ileal digestible (TID) Trp] with L-Trp, five further diets (2-6) containing 1.5-4.2 g Trp/kg were formulated. The dietary Trp content had no effect on amino acid contents in milk on days 20 and 21 of lactation, but Trp in blood plasma on day 28 of lactation reflected the alimentary Trp supply with an increase from 2.74 +/- 1.14 mg/l (diet 1) to 23.91 +/- 7.53 mg/l (diet 6; p < 0.001). There were no directional differences between the diets with regard to the other amino acids. Concentrations of urea in milk and blood were higher with diet 1 (211 and 272 mg/l, respectively) than with diets 3-6 (183 and 227 mg/l, respectively). Serotonin levels in the blood serum were lower with diet 1 (304 ng/ml) than the average of diets 4-6 (540 ng/ml). This study confirms previously given recommendations for the Trp content in the diet of lactating sows, estimated by means of performance, of 1.9 g AID Trp (equivalent to 2.0 g TID Trp; approximately 2.6 g gross Trp) per kg diet.