| A total of 5,450 growing-finishing pigs were used in ten studies to: (1) Determine the effects of added dietary fat and increasing lysine:calorie ratios on growth and economic performance; (2) Predict lysine:calorie ratio requirements based on protein and lipid accretion rates estimated using real-time ultrasound; and (3) Determine the effects of increasing L-lysine HCl on growth performance and carcass characteristics. In Exp. 1, graded levels of added dietary fat (0, 2, 4, and 6%) increased (linear, P < 0.05) ADG and G:F. Carcass characteristics were not affected (P > 0.22). In Exp. 2, the carryover effects of adding and removing fat during the different phases of growth were evaluated. A positive carryover existed during later periods of growth when added fat was included in the previous phase. When adding 6% fat during the first three phases, similar growth performance and improved carcass characteristics were obtained compared with adding fat during all four phases. In Exp. 3 and 4, increasing lysine:calorie ratio increased ADG and G:F (gilts; quadratic, P < 0.01) (barrows; linear, P < 0.01). In both experiments, increasing lysine:calorie ratio decreased (linear, P < 0.01) backfat depth and increased (linear, P < 0.01) percentage lean. In Exp. 5 and 6, the modeled lysine:calorie ratios accurately predicted the lysine:calorie ratio requirements observed in the growth performance experiment. Lysine:calorie ratio requirements (g/Mcal VIE) for pigs used in this experiment can be determined at any body weight (x, kg) by the regression equations (0.00019x2 - 0.05635x + 5.499) for gilts, and (0.000049x2 - 0.037319x + 4.929) for barrows. In Exp. 7, regression equations to predict income over feed cost (IOFQ were developed. The study indicated that IOFC is a better indicator of economic performance than feed cost per pig, or feed cost per kg of gain. In Exp. 8, 9, and 10, increasing L-lysine HCl decreased (linear, P < 0.01) ADG, G:F, and percentage lean in two of the experiments. Results indicate that no more than 0.15% L-lysine HCl should be added to diets for growing-finishing pigs to avoid deficiencies of other amino acids. |
