Effects of Dietary L-Carnitine and Ideal Protein Levels on Carnitine Biosynthesis, Nitrogen Balance and Body Composition of 20 kg Pigs

K.N. Heo, J. Odle, In K. Han, W.T. Cho, S.W. Seo, E. van Heugten and D.H. Pilkington

North Carolina State University Swine Nutrition Research from 1998-2000. Since the discovery of carnitine in the late 1950’s, considerable research has elucidated it’s role in the transport of fatty acids across the inner mitochondrial membrane. But it is not known how well weaning or growing pigs can synthesize carnitine de novo nor how dependant they are on feed carnitine. Previous studies have revealed apparent controversy as to whether supplemental dietary L-carnitine effects pig growth performance (1, 2); however, high dietary carnitine tended to reduce carcass fat accretion, but did not affect protein accretion (1). These results may lead to the suggestion that endogenous carnitine synthesis is sufficient to maintain optimal growth performance, but that added carnitine might alter nutrient partitioning and thus body composition. To examine this problem, we supplemented carnitine into diets which varied in energy:lysine ratio, and studied the effects on carnitine and nitrogen balance (including carnitine biosynthesis). We hypothesized that amino acid degradation would increase in pigs fed a low ME/lysine ratio diet (0.28ME/g lysine, 1.2% lysine , and 4% added fat) without L-carnitine, but that beta-oxidation would increase in the same diet with 500 ppm L-carnitine (increasing the ME used for protein synthesis) and thereby increase protein accretion in supplemented pigs.

Materials and Methods

Pigs (N=25) were used in 5 identical metabolic trials (5 pigs/trial) to study interactive effects of L-carnitine and ideal protein (IP) level on nitrogen (N) and carnitine balance. PIC genotype pigs were fed corn-soybean meal diets (CP 18% or 13.6%) containing either 0 ppm or 500 ppm added L-carnitine (2×2 factorial by randomized complete block design). Diets were formulated to contain 3,400 kcal ME/kg diet and 4% supplemental soy oil, and to exceed requirements for vitamins and minerals (NRC, 1988). The 13.6% CP diet was marginally adequate in protein and contained 0.9% lysine with a ME/lysine ratio of 0.38 kcal ME/g lysine. The 18% CP diet contained 1.2 % lysine with a ME/lysine ratio of 0.28 kcal ME/g lysine. The two different CP diets had the same optimal essential amino acids: lysine ratio (Illinois Ideal protein (IP) II pattern). After 5 d of adaptation to the 18% CP diet without added L-carnitine and feeding frequency (08:00, 20:00), one pig in each trial was killed for initial empty body composition, and 10-d nitrogen and carnitine balance trials were conducted. Nitrogen was measured using the micro-kjeldahl procedure and L-carnitine was measured by using radioisotopic-exchange methodology.

Results and Discussion

High IP feeding increased ADG (P < .01) and empty body weight (P < .01), and L-carnitine tended to increase ADG by 7.2 % (P < .10) and empty body weight (P < .10) also (Table 1). L-carnitine increased plasma free carnitine both after 2hr and 24 hr from last feeding by 2.7 fold (P < .01). Fasting for 24hr did not affect plasma free carnitine concentration (P > .10). High IP feeding improved N digestibility (P < .01), and N retention ratio (P < .01), but increased urinary N excretion by 29% (P < .01). L-carnitine tended to reduce urinary N excretion by 14% (P < .10), and improved biological value (defined as the percentage of absorbed N retained in the body) by 3.3% (P < .05). Body composition data showed that lysine increased N gain (P < .01) and L-carnitine had a tendency to increase N gain in body by 9.9 % (P < .10). Pigs fed 500 ppm Lcarnitine were 1.8 fold higher in empty body carnitine concentration than pigs fed 0 ppm L-carnitine (P < .01). Apparent carnitine balance was computed as (excretion+body gain) – intake. Balance in pigs fed diets with 0 ppm L-carnitine was positive, but balance in pigs fed diets with 500 ppm L-carnitine was highly negative. We speculate that the negative carnitine balance in these animals was due to microbial degradation of L-carnitine in the gastrointestinal tract caused by low efficiency of carnitine absorption from the small intestine when supplemented at 500 ppm (3). Biosynthesis rate of L-carnitine (umol/kg BW/d) in control pigs fed 0 ppm L-carnitine was 3 fold higher than that of adult humans (4)and no difference in empty body carnitine concentration between 54 d and 64 d pigs fed 0 ppm L-carnitine suggested that growing animals need more L-carnitine biosynthesis or supplementation to match their daily body weight gain compared to adult animals. Collectively, these data support the hypothesis that supplemented L-carnitine improves the efficiency of nitrogen utilization by 20 kg pigs.

Table 1. Effects of L-carnitine and ideal protein levels on growth performance, nitrogen balance, and body composition of 20 kg pigs.

^aHigh IP feeding effect (P < .01).
^bcdL-Carnitine effect (P
¹Body weight except for contents of the gastrointestinal tract and urine of bladder at 64 d age.
²Plasma free carnitine was measured both after 2 and 24 hr from last feeding.

References

K.Q. Owen, J.L. Nelssen, R.D. Goodband, T.L. Weeden, and S.A. Blum. 1996. J. of Animal Science. 74:1612-1619.
 
L.A. Hoffman, D.J. Ivers, M.R. Ellersieck, and T.L. Veum. 1993. J. of Anim. Sci. 71:132-138.
 
C.J. Rebouche, D.L. Mack, and P.F. Edmonson. 1984. Biochemistry J. 23:6422-6426.
 
C.J. Rebouche, and C.A. Chenard. 1991. J. of Nutrition. 121:539-546.