L-carnitine supplementation for periparturient dairy cows

L-Carnitine is required for mitochondrial oxidation of long-chain fatty acids. The objectives of this research were to determine whether L-carnitine supplementation increases hepatic fatty acid oxidation and decreases liver lipid accumulation in dairy cows. In experiment 1, 8 mid-lactation cows were abomasally-infused with water or 20 g/d of L-carnitine in combination with ad libitum or restricted dry matter intake. Carnitine infusion increased in vitro fatty acid oxidation by liver slices and prevented liver lipid accumulation during feed restriction. Feed restriction induced higher carnitine concentrations in muscle and milk but not in liver. In experiment 2, L-carnitine was supplemented as a dietary topdress (0, 6, 50, or 100 g/d) from d -14 prior to expected calving date until d 21 after calving. Cows remained on the experiment until d 56 in lactation. Dry matter intake and milk yield were decreased by the 100 g/d treatment. The 50 and 100 g/d treatments caused greater milk fat concentration. Supplementation of 50 and 100 g/d markedly increased in vitro fatty acid oxidation by liver slices on d 2 and 10 after calving, whereas supplementation of 6 g/d stimulated conversion of palmitate to acid-soluble products (ketone bodies) on d 2 but not on d 10. Accordingly, plasma beta-hydroxybutyrate concentrations were elevated in the 50 and 100 g/d treatments in the first 2 wk of lactation. Carnitine supplementation decreased liver triglyceride, increased liver glycogen, and stimulated in vitro conversion of alanine to glucose regardless of supplementation amount. Liver carnitine concentration was not altered by supplementation of 6 g/d but was potently increased by 50 and 100 g/d. Milk carnitine output was increased for all carnitine treatments versus the unsupplemented control treatment. In experiment 3, a cattle-specific 7,872 cDNA microarray was used for transcript profiling using liver samples obtained from experiment 1. Hierarchical clustering revealed that carnitine infusion altered hepatic gene expression patterns in cows fed for restricted and ad libitum feed intake. Expression of several target genes was increased by feed restriction but the effect was dampened by carnitine infusion during feed restriction, indicating that carnitine affects gene expression patterns during negative energy balance.