Evaluation of Standardized Ileal Digestible Tryptophan:Lysine Ratio on Growth Performance and Carcass Characteristics of Finishing Pigs Fed with or without Ractopamine HCl
growth, late finishing pig, ractopamine HCl, tryptophan
Previous research has shown that increasing the SID Trp:Lys ratio up to 24.5% in finishing pigs fed ractopamine HCl (RAC) improved ADG by 0.15 and 0.08 lb/d in comparison with ratios of 18 and 21%, respectively. The objective of the present experiment was to determine the effects of feeding higher SID Trp:Lys ratios with and without RAC on growth performance and carcass characteristics of finishing pigs. A total of 1,101 pigs (PIC 1050 × 327, initially 218.9 lb BW) was used in a 30-d experiment. Pens of 26 pigs were randomly assigned to 1 of 6 dietary treatments arranged in a 2 × 3 factorial, with main effects of RAC (0 or 10 ppm) and SID Trp:Lys (20, 24, and 28%) with 7 replications per treatment. Diets with and without RAC were formulated to 0.90 and 0.66% SID lysine, respectively. Overall (d 0 to 30), RAC × SID Trp:Lys interactions were observed (linear, P < 0.05) where increasing SID Trp:Lys ratio in pigs fed RAC improved BW, ADG, and F/G; however, these criteria decreased when pigs did not receive diets containing RAC. Similarly, RAC × SID Trp:Lys interactions were observed (linear, P < 0.05) for carcass criteria with improvements in carcass ADG, carcass G:F, and HCW when pigs were fed increasing SID Trp:Lys in diets containing RAC, but not without RAC. In summary, increasing SID Trp:Lys ratio to more than 20% improved growth and carcass performance when diets contained RAC, whereas for pigs fed diets without RAC, increasing SID Trp:Lys ratio to more than 20% had poorer performance.
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Soto, J.; Tokach, M. D.; Touchette, K. J.; Dritz, S. S.; Woodworth, J. C.; DeRouchey, J. M.; and Goodband, R. D.
"Evaluation of Standardized Ileal Digestible Tryptophan:Lysine Ratio on Growth Performance and Carcass Characteristics of Finishing Pigs Fed with or without Ractopamine HCl,"
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