Interactions of the Rumen with L-Carnitine When Used as Feed Supplement

Metabolic effects of supplemental L-carnitine have been reported in dairy cows [1], growing steers [2] and growing sheep [3]. It was of interest to investigate whether there is an interaction between the rumen and the supplemental carnitine. Three distinct questions were asked in this context.

Is there any carnitine present in the rumen of non-supplemented ruminants?

Will carnitine be absorbed by the rumen epithelium?

Will carnitine be degraded by rumen microbes?

Methods

The experiments were carried out with six fistulated sheep, 6 to 7 years old, weighing 59 to 68 kg. They were fed a pure hay diet ad lib. Water was available at all times. A bolus of 1 g L-carnitine in the form of Carniking^® was administered for 14 days immediately after the morning feed either directly into the rumen or into the omasum. CrEDTA was used as a rumen fluid marker. Artificial rumen fluid with CrEDTA and with and without L-carnitine was incubated for 3 h in the emptied and washed rumen. Serial samples of rumen fluid and blood were collected over 10 to 12 h.

Results

• 1. L-carnitine was present in normal rumen content at concentrations of 4 to 4 μmol/l. The concentration was unaffected by the time of feeding and was only 5 to 10% of that present in blood plasma. A small but significant amount of L-carnitine was secreted into the emptied and washed rumen at a rate of 15 to 30 μmol/h which amounted to 0.1% of the carnitine pool of the body in three hours.

• 2. L-Carnitine was not absorbed from the isolated and emptied, washed rumen. Three hours of incubation of artificial rumen fluid which contained 500 μmol/l of L-carnitine (10 times higher than blood plasma) resulted in no change in the amount of carnitine in the bathing solution and had no effect on the concentrations of free and total carnitine in blood plasma. Introduction of 1 g of carnitine directly into the omasum for 14 days resulted in a throughout and significantly 20 to 30% higher concentration of total carnitine in plasma than administration of this amount of carnitine into the rumen.

• 3. L-carnitine was extensively degraded in the rumen. When L-carnitine was administered into the rumen together with the rumen fluid marker CrEDTA L-carnitine disappeared about six times faster from the rumen fluid than CrEDTA. The corresponding rate constants of disappearance were 60.2 and 10.5%/h, respectively. Since carnitine was not absorbed from the rumen, from this it can be concluded that only 17% of the administered carnitine passed out of the rumen with the rumen fluid. The remaining fraction was probably degraded.

Summary and conclusions. L-Carnitine is not absorbed by the rumen epithelium. Instead, there is a small but significant secretion of carnitine across the epithelium into the rumen. L-carnitine is extensively degraded in the rumen. Its rate of disappearance from the rumen is about six times faster than that of CrEDTA. When L-carnitine is used as a feed supplement for ruminants carnitine should either be protected from being degraded in the rumen or losses through microbial degradation should be taken into account.