Determining the Optimal Threonine:Lysine Ratio in Starter Diets for the Segregated Early-Weaned Pig

Kansas State University Swine Research. A 14-day growth trial was conducted to determine the threonine:lysine ratio necessary to optimize growth performance of the segregated early-weaned (SEW) pig. Twelve experimental diets included two levels of lysine (1.15% and 1.5% apparent digestible lysine) and six apparent digestible threonine: lysine ratios (40, 45, 50, 55, 60, and 65%) in a 2 6 factorial arrangement. Growth performance was improved by feeding 1.5% rather than 1.15% digestible lysine. Growth performance decreased linearly as the digestible threonine:lysine ratio increased. Although a significant quadratic response was not observed, this reduction in growth performance did not appear to occur until the threonine ratio exceeded 45% of lysine on an apparent digestible basis. These data indicate that the threonine requirement for the SEW pig is approximately 45% of digestible lysine.