Performance of Weanling Pigs Fed Increasing Levels

Experiments were conducted to estimate the threonine requirement of pigs weighing 5 to 15 kg and to determine whether excess methionine increased the threonine requirement. Feeding .70% dietary threonine in Exp. 1 maximized (P<.01) gain/feed and minimized (P<:01) plasma urea N. Plasma threonine was increased (P<.01) by threonine supplementat ion and the rate of increase accelerated above .65% dietary threonine. Threonine supplementat ion did not affect plasma methionine, t ryptophan and(or) lysine, but it increased leucine (P<.01) and isoleucine (P<.05). In Exp. 2, additions of .40% methionine and(or) .30% threonine to a 16% crude protein diet that had calculated concen trations of .57% sulfur amino acids and .68% threonine did not affect (P>.10) pig .performance or plasma urea N. In Exp. 3, a 15% crude protein diet that had calculated concentrations of .54% sulfur amino acids and .61% threonine was supplemented with .40% methionine and(or) .15% threonine. Amino acid addit ions did not affect performance of pigs, but pigs fed supplemental threonine had the least plasma urea N, indicating that .61% dietary threonine was marginally deficient for pigs weighing 5 to 15 kg. (