Tryptophan Needs of Lactating Sows Fed High Lysine Diets

Researchers have recently attempted to minimize the negative nutrient balance status of the high producing lactating sow by increasing the nutrient density of the lactation diet. Stahly et al. (1990) and Tokach et al. (1991 b), have reported increases in sow productivity due to feeding higher crude protein levels during lactation. Throughout the industry, these responses have been attributed mostly to lysine, the most limiting amino acid in corn-soybean meal diets. Synthetic lysine has been used as an economically viable alternative to soybean meal in lactation diets, but excessive use could create deficiencies of other essential amino acids. Tryptophan is found in very small amounts in corn (NRC, 1988) and is most often the second limiting amino acid in corn based diets (ARC, 1981). Tryptophan is known to have many metabolic roles besides being an essential component of body muscle tissue (Sidransky, 1985). Marginal or limiting tryptophan levels in swine diets have been shown to have a marked effect on feed intake (Uttecht et al., 1991), a major obstacle in minimizing the negative nutrient balance status of lactating sows. The objective of our experiment was to determine if the responses of increased productivity sometimes occurring in high producing lactating sows fed high protein levels (≥16%) are due entirely to lysine or if tryptophan is involved as well