Dietary L-carnitine improves nitrogen utilization in growing pigs fed low energy, fat-containing diets

Growing pigs (n = 25; 17.8 +/- 0.1 kg) were used to study the effects of L- carnitine and protein intake on nitrogen (N) balance and body composition. Fat-supplemented (40 g soy oil/kg diet), corn-soybean meal basal diets cont aining low or high protein (136 or 180 g/diet) were formulated so that prot ein accretion would be limited by metabolizable energy (ME), Each basal die t was supplemented with 0 or 500 mg/kg L-carnitine and fed to pigs for 10 d in a nutrient balance trial. Final body composition was compared with weig ht and age-matched pigs measured on d 0 to calculate nutrient accretion rat es. High protein feeding increased (P < 0.01) average daily gain (ADG) by 3 4%, as well as nitrogen digestibility (4.4%), retention (5.2%), urinary exc retion (29%) and crude protein (CP) accretion (33%). Total-body carnitine a ccretion rate was 4.5 fold greater and total body carnitine concentration w as almost 100% greater than in unsupplemented controls (P < 0.01). irrespec tive of protein level, carnitine increased ADG (by 7.3%, P < 0.10) and CP a ccretion rate (9%, P < 0.10). Congruently, carnitine supplementation improv ed the efficiency of nitrogen retention (P < 0.05) and reduced urinary nitr ogen excretion (14%, P < 0.10). Carcass fat content also was reduced in car nitine-supplemented pigs (P < 0.10). Collectively, these data support the h ypothesis that carnitine can improve the efficiency of nitrogen utilization in 20-kg pigs fed energy-limited, fat-containing diets. We conclude that e ndogenous carnitine biosynthesis may be adequate to maintain sufficient tis sue levels during growth, but that supplemental dietary carnitine (at 500 m g/kg) may be retained sufficiently so as to alter nutrient partitioning and thus body composition of 20-kg pigs.