The influence of short-term feeding of amino acid-deficient diets and high dietary leucine levels on the intramuscular fat content of pig muscle

The objective of the study was to investigate the influence of amino acid-deficient diets and high dietary leucine levels offered for intervals of either 22 or 35 days pre-slaughter on the intramuscular fat content of pig muscle. Twenty-four hybrid gilts were offered individually ad libitum one of four diets that comprised combinations of amino acid levels (supplemented or deficient: 5.6 v. 4.0 g lysine per kg) and low or high leucine levels (10.3 v. 30.3 g leucine per kg). Live weights at the start of the study were 74.5 and 87.0 kg for pigs on the 35- and 21-day feeding regimens, respectively. There were no significant effects of dietary amino acid level, leucine level, or feeding interval on food intake, daily live-weight gain or food efficiency. Pigs given the amino acid-deficient diets had lower killing-out proportions (736 v. 747 (s.e. 3.4) g/kg; P <0.05) and longissimus dorsi muscle areas (32.6 v. 35.7 (s.e. 0.71) cm(2), P <0.01) than those given amino acid-supplemented diets. Subjective score for longissimus dorsi colour indicated that pigs on the high leucine diet had darker muscle than those on the low leucine diet. Intramuscular fat contents of the longissimus dorsi muscle at the 10th/11th rib and the 3rd/4th lumbar vertebra and of the semimembranosus muscle were increased by 19, 18 and 18 g/kg, respectively (P <0.05), for pigs given amino acid-deficient compared with those given amino acid-supplemented diets. Dietary leucine level had no significant effect on intramuscular fat level. Pigs given the diets for 35, compared with 21, days had higher fat levels in the semimembranosus muscle (52 v. 30 (s.e. 5.2) g/kg; P <0.01) but not in the other two muscle locations studied. This study suggests that relatively short-term feeding of amino acid-deficient diets can produce substantial increases in intramuscular fat levels.