L‐Carnitine and level of feed intake alter hepatic nutrient metabolism and tissue carnitine distribution in lactating dairy cows

Abstract

Dairy cows are prone to excessive hepatic lipid accumulation around parturition. Carnitine stimulates fatty acid oxidation by bovine liver slices and may prevent or reduce hepatic lipid accumulation. Eight lactating cows were used in a replicated 4 × 4 Latin square design. Treatments were factorial combinations of feed intake (FI) restriction and abomasal carnitine (20 g/d) infusion: water infusion + ad libitum FI (WA), water infusion + restricted FI (WR), carnitine infusion + ad libitum FI (CA), carnitine infusion + restricted FI (CR). Each period of 14 d consisted of infusions on d 5–14, restricted FI imposed on d 10–14, and liver and muscle biopsies obtained on d 14 of each period. Milk was sampled on d 9 and 14. L-carnitine infusion increased the rate and proportion of palmitate oxidation and decreased the proportion of palmitate esterified by liver slices (P < 0.05). Liver triacylglycerol concentration tended to be lower (P < 0.10) in WA, CA, and CR (0.3% wet basis) than in WR (0.9%). Restricted FI reduced propionate conversion to CO2 by liver slices. Alanine conversion to CO2 was higher in CA versus other treatments. Conversion of alanine and propionate to glucose was unaffected by treatment. Liver carnitine was not altered in WR compared with WA, but was elevated in CR versus CA. Muscle carnitine was increased by carnitine infusion and restricted FI without interaction. Carnitine infusion increased milk carnitine content on d 9, while carnitine infusion and restricted FI increased milk carnitine content on d 14. L-Carnitine prevents hepatic lipid accumulation in feed-restricted lactating dairy cows. Supported by Lonza, Inc. (Allendale, NJ).