Effects of low protein diets on pigs with a lean genotype. 1. Carcass composition measured by dissection and muscle fatty acid composition

Pigs with a lean genotype were fed diets differing in protein and amino acid contents between 40 and 115 kg live weight. A high protein control regime (C) was compared with one supplying 11% less total protein but the same essential amino acid levels (LP1) and one supplying 16% less protein but lower amino acid levels (LP2). Regime LP2 produced fatter pigs in terms of subcutaneous, intermuscular and intramuscular fat (IMF), the latter measured in longissimus and semimembranosus muscles. The percentage of linoleic acid was lowest and that of oleic acid highest in IMF from LP2 pigs (11.57 and 34.59% respectively in longissimus). Pigs in regime LP1 had more longissimus IMF than C but similar semimembranosus IMF although both muscles had lower percentages of linoleic acid in LP1 than C, suggesting a tendency towards greater fat deposition in LP1. The high IMF content in LP2 produced the most tender, juicy steaks.