Growth performance and carcass traits of pigs subjected to marginal dietary restrictions during the grower phase

Sixty-four individually housed pigs were used to investigate the effect of amino acid content of finisher diets on growth performance of pigs subjecte d to marginal dietary amino acid restrictions (80% of the 1988 NRC lysine r ecommendation) during the grower phase. In each of the two trials, low- and high-amino-acid grower diets (.421 and .765 g lysine/MJ DE, respectively) and four finisher diets (.421, .516, .612, and .707 g lysine/MJ DE) were ra ndomly assigned within sex to 16 gilts and 16 castrated males weighing 23.0 +/- 2.0 kg in a 2 x 4 factorial arrangement of treatments. The average wei ght of pigs after a completion of diet change was 50.4 +/- 2.1 kg. All pigs were slaughtered at an average weight of 105.2 +/- 4.1 kg. Ultrasound back fat thickness was measured at the time of diet change and before slaughter. Pigs were allowed ad libitum access to feed and water. During the grower p hase, pigs fed the high-amino-acid diet grew faster (P < .001) and mole eff iciently(P < .001) and had less ultrasound backfat (P < .001) than those fe d the low-amino-acid diet. The grower diet had no effect on weight gain dur ing the finisher phase. Consequently, pigs fed the high-aminoacid grower di et had better overall weight gain (P < .01) than those fed the low-amino-ac id diet. The rate of lean accretion was, however, similar between the two g roups of pigs. Furthermore, pigs fed the low-amino-acid grower diet seemed to have better carcass quality, as indicated by less ultrasound backfat (P < .01) and larger carcass longissimus muscle area (P < .05). Average and 10 th rib carcass backfat decreased linearly (P less than or equal to .05) and lean accretion rate improved linearly ( P < .05) as the amino acid content of finisher diets increased, but there was no grower x finisher diet inter action in these and other response criteria. Although no evidence of compen satory weight gain was observed, it is possible that compensatory lean tiss ue growth may have occurred in pigs subjected to early amino acid restricti ons at the expense of fatty tissue growth.