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An experiment with twenty male 10-week-old crossbred pigs [(German Landrace x Large White) x Pietrain] with an average body weight of 21 kg was conducted. One group of pigs received the basal diet without further supplementation (control diet). The analysed lysine concentration of that diet was 9.7 g/kg. The second group received the same basal diet supplemented with 7 g L-lysine hydrochloride at the expense of barley (high-lysine diet). The analysed lysine concentration of that diet was 16.8 g/kg. Concentrations of all the other amino acids did not differ between the diets. The diets had a low concentration of L-carnitine (5 mg/kg). Animals were given free access to diet. To control the feed intake, unconsumed feed was weighed weekly. Water was available ad libitum from a nipple drinker system. Diets were administered for 2 weeks.
Pigs fed the high lysine diet had lower concentrations of free and total carnitine in plasma, liver, kidney and skeletal muscle than control pigs (P<0.05). Pigs fed the high-lysine diet moreover had an increased concentration of trimethyllysine (TML), a reduced mRNA abundance of TML dioxygenase and reduced concentrations of g-butyrobetaine (BB) in muscle, indicating that the conversion of TML into BB in muscle was impaired. Concentrations of BB, the metabolic precursor of carnitine, in plasma, liver and kidney were also reduced in pigs fed the high-lysine diet while the activity of BB dioxygenase in kidney was not different and that in liver was even increased compared to control pigs (P<0.05).
In conclusion, this study shows that a moderate dietary excess of lysine lowers plasma and tissue carnitine concentrations in pigs. Reduced concentrations of BB in liver and kidney suggest that the depressed carnitine status was likely caused by a decreased rate of carnitine synthesis due to a diminished availability of carnitine precursor, probably mainly as a result of an impaired BB formation in muscle.
M Fischer, F Hirche, H Kluge and K Eder. 2009. British journal of Nutrition. 101:190-196.
