THE INFLUENCE OF SHORT-TERM FEEDING OF AMINO ACID-DEFICIENT DIETS ANDHIGH DIETARY LEUCINE LEVELS ON THE INTRAMUSCULAR FAT-CONTENT OF PIG MUSCLE

The objective of the study was to investigate the influence of amino a cid-deficient diets and high dietary leucine levels offered for interv als of either 22 or 35 days pre-slaughter on the intramuscular fat con tent of pig muscle. Twenty-four hybrid gilts were offered individually ad libitum one of four diets that comprised combinations of amino aci d levels (supplemented or deficient: 5.6 v. 4.0 g lysine per kg) and l ow or high leucine levels (10.3 v. 30.3 g leucine per kg). Live weight s 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 e ffects 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-s upplemented diets. Subjective score for longissimus dorsi colour indic ated that pigs on the high leucine diet had darker muscle than those o n 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, re spectively (P <0.05), for pigs given amino acid-deficient compared wit h those given amino acid-supplemented diets. Dietary leucine level had no significant effect on intramuscular fat level. Pigs given the diet s for 35, compared with 21, days had higher fat levels in the semimemb ranosus muscle (52 v. 30 (s.e. 5.2) g/kg; P <0.01) but not in the othe r two muscle locations studied. This study suggests that relatively sh ort-term feeding of amino acid-deficient diets can produce substantial increases in intramuscular fat levels.