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

Kansas State University Swine Research. A 14-d growth trial was conducted to evaluate effects of increasing isoleucine: lysine ratios on growth performance of the segregated early-weaned pig. Twelve experimental diets included two levels o f lysine (1.15% and 1.50% digestible lysine) and six digestible isoleucine:lysine ratios (40, 45, 50, 55, 60, and 65% relative to lysine) in a 2 6 factorial arrangement. From d 0 to 14, growth performance was improved by feeding 1.50% digestible lysine. A linear improvement in growth performance occurred from d 0 to 7 as the isoleucine:lysine ratio increased. Although a significant quadratic response was not observed, little improvement in pig performance occurred above the 60% apparent digestible isoleucine:lysine ratio. Increasing isoleucine had no effect on the overall gr owth performance from d 0 to 14, but pla sma urea nitrogen (PUN) was linearly reduced on d 14. These data suggest that the isoleucine requirement for the SEW pig is approximately 60% of lysine on an apparent digestible basis. However , because this response was observed only in the first week postweaning, further research is required to confirm this high a requirement for isoleucine.