SUMMARY

Chiba, L. I., D. L. Kuhlers, L. T. Frobish, S. B. Jungst, E. J. Huff-Lonergan, S. M. Lonergan, and K. A. Cummins.

Sixty-four pigs, 32 pigs selected for lean growth efficiency and 32 control pigs selected randomly, were used to investigate the effect of genotype and realimentation diets on growth performance and carcass quality of pigs subjected to marginal dietary restrictions during the grower phase. When pigs weighed approximately 20 kg, 16 pens containing two gilts and 16 pens containing two castrated males were randomly assigned within genetic lines to grower diets and finisher diets in a 2 x 2 x 2 factorial arrangement of treatments. Grower diets contained 0.421 or 0.765 g lysine/MJ DE, whereas finisher diets contained 0.421 or 0.612 g lysine/MJ DE.

Genotype had no effect on growth performance, but select line pigs had better carcass quality (P < 0.05) and seemed to utilize amino acids more efficiently for growth than control line pigs as indicated by lower blood urea nitrogen (P = 0.07). During the grower phase, pigs fed the high-amino acid grower diet grew faster and more efficiently (P < 0.01) and had less ultrasound backfat (P < 0.001) than those fed the low-amino acid diet. Although some grower x finisher diet interactions were observed, there was no indication that pigs subjected to early amino acid restrictions exhibited compensatory weight gain, or had different amino acid requirements in the subsequent phase. The rate of lean accretion was similar between pigs fed the low- and high-amino acid grower diets regardless of genotype, indicating that compensatory lean tissue growth may have occurred in pigs subjected to early amino acid restrictions. Furthermore, restricted pigs had better feed efficiency in the subsequent phase, which may have a positive impact on the environment by reducing the excretion of unutilized nutrients. Select line pigs fed the low-amino acid grower diet had lower overall weight gain compared with other groups (genotype x grower, P < 0.001).

The results indicate that compensatory lean tissue growth may have occurred in pigs subjected to early amino acid restrictions, but pigs selected for lean growth efficiency may be less tolerant of early amino acid restrictions. Therefore, offering a grower diet containing adequate amino acids might be important in optimizing overall growth performance of select line pigs.

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