Betaine suppresses carnitine palmitoyltransferase I in skeletal muscle but not in liver of finishing pigs

An experiment was conducted to investigate the effect of dietary betaine supplementation on the enzyme activity and mRNA abundance for carnitine palmitoyltransferase I (CPT I) in liver and skeletal muscle of finishing pigs. Forty-eight crossbred barrows and gilts [Duroc × (Seghers × Seghers)] weighing about 55 kg were divided into two dietary treatments, each with three replicates of eight pigs (four barrows and four gilts) per replicate. Pigs were fed a corn–soybean meal basal diet supplemented with betaine at 0 or 1250 mg/kg feed for 42 days. At trial termination, two pigs (one barrow and one gilt) weighing about 90 kg were selected from each replicate (six pigs per dietary treatment) and slaughtered for analyses. The results showed that intramuscular fat content in the longissimus muscle of pigs fed betaine was 23.6% higher than that of controls (P < 0.05), whereas hepatic fat content was not affected with dietary betaine treatment. Muscle-type CPT I (M-CPT I) activity, but not liver-type CPT I (L-CPT I) activity was decreased by betaine supplementation. Furthermore, betaine supplementation reduced M-CPT I mRNA abundance by 14.6% (P < 0.05) but did not affect L-CPT I mRNA abundance. There was a positive correlation between enzyme activity and mRNA abundance for both L-CPT I and M-CPT I (r = 0.67 and r = 0.72 for L-CPT I and M-CPT I, respectively; P < 0.05). The study suggests that betaine may be involved in fat partitioning in pigs by reducing the activity and mRNA abundance of M-CPT I, with a resultant increase in intramuscular fat content.