AMINO-ACID-REQUIREMENTS OF GROWING-PIGS .1. EFFECTS OF REDUCING PROTEIN LEVEL IN DIETS CONTAINING HIGH-LEVELS OF LYSINE

Sixty-four growing pigs, with equal numbers of females and castrated males, were fed diets containing from 10 to 17·6% crude protein but in which lysine was maintained at 0·95%. Over the 25 kg to 55 kg live-weight range studied, growth performance was unaffected by a reduction in crude protein level from 17·6 to 14·5%. Below 14·5% crude protein, daily live-weight gain and feed conversion ratio deteriorated linearly. Percentages of lean meat and fat in the middle joint showed similar trends. Significant sex effects were confined to carcass characteristics which indicated that the females produced leaner carcasses. It was concluded that below 14·5% crude protein a deficiency of the next limiting amino acid to lysine, or possibly non-essential nitrogen, depressed growth performance. © 1979, British Society of Animal Science. All rights reserved.