The optimal true-ileal-digestible lysine and total sulfur amino acid requirement for nursery pigs between 20 and 50 LB
Kansas State University Swine Day 2004. An experiment was conducted with 360 pigs (PIC, avg BW = 22.7 lb) to determine the appropriate true-ileal-digestible (TID) lysine and total sulfur amino acid (TSAA) requirement of nursery pigs, and consequently to determine the optimal TSAA-to-lysine ratio. This trial was organized as a combination of two simultaneous experiments, with one set of diets consisting of five treatments with increasing TID lysine (0.9, 1.0, 1.1, 1.2, and 1.3%) and the second set of diets consisting of five treatments with increasing TID TSAA (0.56, 0.62, 0.68, 0.74, and 0.81%). The highest concentrations of both lysine and TSAA (1.3% and 0.81%, respectively) were combined as one diet and used in both the lysine and TSAA titrations, to give a total of 10 treatments. Pigs were randomly allotted to eight replications with five pigs per pen, on the basis of BW. Average daily gain increased (linear, P<0.01), but ADFI decreased (linear, P<0.06) with increasing TID lysine. Increasing TID lysine also improved (linear, P<0.01; and quadratic P<0.05) F/G. Increasing TID TSAA from 0.56 to 0.81% increased (linear, P<0.02) ADG and improved (linear, P<0.01) F/G. The arrangement of treatments in this experiment determined both the lysine and TSAA requirements simultaneously, which allowed the use of a regression approach in the establishment of a TID TSAA-to-lysine ratio. In this approach, ADG and F/G values are plotted as the dependent variables on the X axis and the TID lysine and TSAA concentrations are plotted on the Y axis. A trend line is fit through the data to develop a regression equation to predict the TID lysine and TSAA requirements, which can be used to estimate the TID TSAA-to-lysine ratio. The values for ADG and F/G from the individual lysine and TSAA trials must overlap to allow this approach to work. Regression analysis of the response surface resulted in an estimated TID TSAA-to-lysine ratio range of 55 to 61% for ADG and 57 to 61% for F/G.