THE USE OF SYNTHETIC LYSINE IN THE DIET OF LACTATING SOWS

We conducted an experiment to determine the proportion of the lysine r equirement of lactating sows that can be met using L-lysine . HCl. A t otal of 247 Pig Improvement Company (PIC) sows (parity one to four) we re randomly allotted to one of five experimental diets containing .79% apparently digestible lysine. The first four diets contained 0, .075, .150, and .225% L-lysine . HCl replacing the intact lysine, primarily derived from soybean meal. Dietary crude protein was reduced from 17. 9 to 16.9, 15.8, and 14.8% respectively. The fifth diet contained .174 % L-lysine . HCl (15.5% CP) with added synthetic methionine, threonine , and tryptophan to restore the ratios of these amino acids to lysine to those in the control diet with no synthetic amino acids. The averag e lactation length was 15.7 +/- .3 d. Diet did not affect ADFI, sow ba ckfat loss, sow loin eye area loss, or weaning-to-mating interval. Sow s consumed an average of 4.6 kg/d and were provided 36 g/d of digestib le lysine. Replacing soybean meal with increasing levels of L-lysine . HCl did not affect sow weight change. The number of pigs weaned decre ased and preweaning mortality increased linearly(P = .08) with increas ing levels of L-lysine . HCl. Litters from sows fed the .174% L-lysine . HCl with added methionine, threonine, and tryptophan grew slower an d had a higher mortality rate than litters from sows fed no synthetic amino acids(P < .05). The addition of synthetic methionine, threonine, and tryptophan to the .174% L-lysine . HCl diet did not improve litte r growth rate, but it did increase preweaning mortality(P = .05) and d ecrease the number of pigs weaned (P = .06) compared to the .15% L-lys ine . HCl with no additional synthetic amino acids. These additions al so resulted in an increased sow weight loss (P = .10). These results s uggest that when more than .075% L-lysine . HCl is used to meet the ly sine requirement preweaning mortality is increased and the number of p igs weaned is decreased. Supplementation with methionine, threonine, a nd tryptophan failed to ameliorate the negative response associated wi th L-lysine . HCl, which suggests that other amino acids may be limiti ng.