Dose-dependent response of intramuscular fat accumulation in longissimus dorsi muscle of finishing pigs to dietary lysine levels

In order to elucidate response of accumulation of intramuscular fat (IMF) in longissimus dorsi (l. dorsi) muscle of finishing pigs to different levels of dietary lysine, we conducted a feeding trial where we prepared test diets of four levels of lysine, 4.0, 4.8, 5.6, and 6.4 g/kg diet. Twenty barrows and 20 gilts, Duroc×(Large White×Landrace) cross breed, from seven litters aged approximately 100 days were used. The average initial body weight was 58.4±3.3 kg. The diets were iso-energetic and iso-nitrogenous, and contained equal amounts of indispensable amino acids apart from lysine. The diets contained all indispensable amino acids apart from lysine in the recommended amounts. When the pigs reached an average body weight of 110 kg, they were slaughtered. After chilling overnight, l. dorsi muscle samples were taken. Live weight gain and feed efficiency linearly responded to the change of dietary lysine levels (P<0.01); the lower the lysine content was, the lower the weight gain and the feed efficiency were. Back fat depth and carcass yield were not affected by dietary lysine levels. Although l. dorsi area was the smallest in the 4.0L group, the effect of the dietary lysine levels was not statistically significant. Concentration of IMF in l. dorsi muscle was affected by the dietary lysine levels; the response was linearly dose-dependent (P<0.01) and a tendency of quadratic effect was observed (P=0.062); pigs given a lower lysine diet (4.0 or 4.8 g/kg lysine) had higher concentrations of IMF in l. dorsi muscle than those given a higher lysine diet (5.6 or 6.4 g/kg diet). As the effects of dietary lysine levels on concentration of IMF in l. dorsi muscle of finishing pigs were dose-dependent, we conclude that it can be regulated by adjusting dietary lysine levels.