TRYPTOPHAN NEEDS OF LACTATING SOWS FED DIETS SUPPLEMENTED WITH CRYSTALLINE LYSINE

Large White x Landrace primiparous and multiparous sows (n = 115) were used to evaluate the tryptophan needs of lactating sows fed diets sup plemented with crystalline lysine to contain .75% lysine. Sows were fe d 1.8 kg of their allotted diets from d 110 of gestation until parturi tion and then were allowed ad libitum access to diets analyzed to cont ain either .12 (n = 58) or .17% (n = 57) tryptophan during a 21-d lact ation. Diets were created by crystalline tryptophan and lysine additio ns to a corn-soybean meal basal diet that contained .12% tryptophan. T ryptophan level in the lactation diet did not affect number or weight of pigs at 21 d (P > .10). Sows fed .17% tryptophan were heavier at d 21 of lactation than those fed .12% tryptophan (P = .09) due to less w eight loss during the 21-d lactation (P = .09). Feed intake was greate r (P < .05) for sows fed .17% tryptophan than for sows fed .12% trypto phan. A reference diet analyzed to contain .11% tryptophan and .63% ly sine was fed to an additional 11 sows only as a baseline for measuring plasma urea nitrogen and amino acids. Plasma tryptophan concentration s were higher (P < .05) for sows fed .17% tryptophan than for sows not fed added L-tryptophan. Among sows fed the low-tryptophan diets, sows fed the reference diet (.60% lysine) had higher (P < .05) plasma phen ylalanine and valine concentrations than sows fed .75% lysine. Diet di d not affect plasma concentrations of any other essential amino acid ( P > .10). Plasma urea N levels were lower (P = .11) for sows fed the d iet supplemented with tryptophan. Lactating sows allowed ad libitum ac cess to diets containing .75% lysine benefited from higher feed intake and lower weight loss when dietary tryptophan levels were increased f rom .12 to .17%.