A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of dietary
amino acid contents during the grower (G) phase and selection for lean growth efficiency on growth performance, carcass traits, and meat quality. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two castrated males per pen, and pens were randomly assigned within the genetic line to corn-soybean meal G diets formulated to contain 5.0, 7.0, 9.0, or 11.0 g
lysine/kg. After 50 kg, all pigs were fed common finisher 1 (F1) and finisher 2 (F2) diets. Pigs were allowed ad libitum access to feed and water. After the initial statistical analyses, the data sets from the two trials were combined. During the G phase, pigs consumed less feed [linear (Ln), P < 0.001] and more
lysine (Ln, P < 0.001), grew faster (Ln, P < 0.05) but utilized feed more and
lysine less efficiently (Ln, P < 0.001) for
weight gain as the
amino acid content of G diets increased. Increasing dietary
amino acids resulted in less ultrasound backfat (Ln, P < 0.001) and more serum
urea nitrogen [Ln, P < 0.001; quadratic (Qd), P < 0.01] at the end of the G phase. Pigs grew more slowly during the F1 (Ln, P < 0.01 and Qd, P = 0.05) and F2 (Ln, P = 0.07) phases and utilized feed and
lysine less efficiently (Ln, P < 0.05) for
weight gain during the F1 phase as the
amino acid content of G diets increased. The grower diet had no effect on overall
weight gain and feed efficiency, carcass traits, or meat quality scores. The efficiency of
lysine utilization for overall
weight gain (Ln, P < 0.001) and lean accretion (Ln, P < 0.05) improved as the
amino acid content of G diets decreased. The SL pigs grew faster (P < 0.05) and had less (P < 0.001) ultrasound backfat throughout the study compared with the CL pigs. The SL pigs had less 10th rib backfat (P < 0.001) and tended to have larger longissimus muscle area (P = 0.09) than the CL pigs, which were reflected in greater rate (P < 0.001) and efficiency (P < 0.05) of lean accretion. Marbling (P < 0.05) and meat color (P = 0.07) scores were lower in the SL pigs. No grower diet x genotype interactions were observed in response criteria of interest. The results indicate that pigs subjected to dietary
amino acid restrictions during the G phase (as low as 5.0 g
lysine/kg) compensated completely in terms of growth rate and body composition regardless of the genotype. Compensatory growth can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing excretion of unused nutrients.