Four 28-d trials were conducted using a total of 432 pigs, with average initial weight across trials ranging from 6.3 to 9.7 kg, to estimate the
tryptophan (trials 1 and 2) and
threonine (trials 3 and 4) requirements of pigs fed low
protein, corn-sunflower meal diets. The effect of
tryptophan,
threonine and
protein level on serum
calcium,
phosphorus and
zinc also was studied. The diets contained either 12 or 13%
protein and were calculated to be adequate in all nutrients except crude
protein and the
amino acid being investigated. A
lysine supplemented, 18%
protein, corn-sunflower meal diet was included in all trials as a positive control. In trial 1,
weight gains of pigs increased linearly (P less than .005) while feed conversion improved cubically (P less than .05) as dietary
tryptophan increased from .14 to .22%. Pigs fed the 18%
protein diet gained faster (P less than .05) and required less feed/gain than pigs fed
low protein diets. In trial 2,
weight gains improved quadratically (P less than .005) and feed conversion improved linearly (P less than .05) as dietary
tryptophan increased from .104 to .204%. Serum
phosphorus and
zinc concentrations were lower (P less than .05) in pigs fed the 18%
protein diet. In both trials, serum
urea N responded quadratically (P less than .05) to increasing dietary
tryptophan, and was lower (P less than .05) in pigs that were fed diets supplemented with
L-tryptophan than in those fed the low
protein basal or 18%
protein diets.(ABSTRACT TRUNCATED AT 250 WORDS)