Threonine requirement of pigs weighing 5 to 15 kg.

Weanling crossbred pigs (avg initial wt 6.4 kg) were fed diets containing six levels of threonine to determine the threonine requirement of young pigs fed diets somewhat similar to those used in commercial swine production. The diets (16% crude protein) were composed primarily of grain sorghum, oat groats and soybean meal supplemented with minerals, vitamins, lysine, tryptophan, methionine and isoleucine, and were calculated to be adequate in all nutrients except threonine and crude protein. Threonine levels were .53, .57, .62, .68, .75 and .83% of the diet. There were two trials, each with 96 pigs. The pigs were fed the experimental diets for 28 d. The addition of threonine increased weight gain (P less than .02) and feed efficiency (P less than .001), with most of the response occurring between .53 and .68% threonine. There was little further response when threonine was increased above .68%. Plasma threonine concentrations increased as dietary threonine increased, with a sharp rise when dietary threonine exceeded .68%. Concentrations of most other essential amino acids in the plasma declined in response to increasing dietary threonine, and reached minimum values at either .68 or .75% threonine. Plasma urea concentrations decreased as threonine was increased in the diet, reaching a plateau at .68% dietary threonine. The data indicate the young pigs weaned at 3 to 4 wk of age require approximately .70% threonine.