Effect of Dietary Lysine on the Skeletal Muscle Intramuscular Fat Content and Fatty Acid Composition of Late-Stage Finishing Pigs

Pork eating quality can be largely influenced by the intramuscular fat (IMF) content and its fatty acid (FA) composition in the skeletal muscle. This study was conducted to investigate if dietary lysine at different levels could affect the IMF content and its FA composition of longissimus muscle in late-stage finishing pigs. Nine crossbred barrows (94.4 ± 6.7 kg BW) were randomly allotted to three dietary treatments (3 pigs/treatment). Three corn and soybean-meal based diets were formulated to meet the NRC (2012) recommended requirements of various nutrients for late-stage finishing pigs, except for the lysine content, which were 0.43, 0.71, and 0.98% (as-fed basis) for Diets 1 (lysine-deficient), 2 (lysine-adequate), and 3 (lysine-excess), respectively. During the 5 week feeding trial, pigs were allowed ad libitum access to their respective diets assigned and fresh water. At the end of the trial, pigs were harvested and muscle samples were collected from the middle portion (between the 10^th and 12^th ribs) of longissimus dorsi. Fatty acids in the samples were directly derivatized and measured using a gas chromatographic method. The IMF content of the longissimus muscle, calculated as total FA, was increased (P < 0.05) with the decreased dietary lysine content (from Diet 3 to Diet 1). Dietary lysine level did not affect the percentages of individual and total saturated FA, except for that of stearic acid (C18:0), which tended to be reduced with Diet 1 (P = 0.09). In terms of unsaturated FA, the percentage of oleic acid (C18:1 n-9) and total mono-unsaturated FA were greater (P < 0.05), whereas that of linolenic acid (C18:3 n-3) were less (P < 0.05), in the pigs fed Diet 1 than the pigs fed Diet 2. These results suggest that the IMF content of longissimus muscle of late-stage finishing pigs can be increased with reduced level of dietary lysine. Dietary lysine level can also alter the proportions of FA, especially that of mono-unsaturated FA, which improve pork nutritive values and eating quality. Further research, however, is needed to study if transient use of a lysine-deficient diet can improve pork eating quality via altering the IMF content and its FA composition without compromising the growth performance of pigs at their late finishing stage. This project was supported by USDA Hatch/Multistate Project 1007691.