Effects of L-carnitine supplementation in diets with low or normal energy level on growth performance and carcass traits in broilers

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1 Effects of L-carnitine supplementation in diets with low or normal energy level on growth performance and carcass traits in broilers S. ÇAKIR 1 * and S. YALÇIN 2 1 University of Abant zzet Baysal, Mudurnu Süreyya Astarcı Vocational School of Higher Education, Bolu, TURKEY. 2 University of Ankara, Veterinary Faculty, Department of Animal Nutrition and Nutritional Disease, Ankara, TURKEY. * Corresponding author: cakirsf@yahoo.com ; cakir-s@ibu.edu.tr SUMMARY The aim of the present experiment is to determine the effects of a dietary L-Carnitine supplementation on growth parameters, carcass composition, and some serum biochemical markers (total cholesterol, protein and albumin concentrations) in broiler chickens according to the energy level of the ration. 288 one day old ROSS 308 broiler chicks were equally divided into 4 groups (n = 72): birds of the groups I and II were fed with energy-depressed diets supplemented or not with L carnitine (100 mg/kg of food) respectively whereas the 2 other groups received diets with a normal energy level supplemented (group IV) or not (group III) with L carnitine. Carcass weights and their corresponding indexes were significantly lowered in birds with energydepleted diets. Mortality rates and growth parameters (body weights, weight gains, food intake and food conversion ratio) did not significantly differ between groups although the dietary L carnitine supplementation appeared to weakly improve the growth of birds receiving low energy diets (group II). However, L carnitine induced significant increases of the liver weights and of serum albumin concentrations in dietary energy depleted birds (group II) compared to the respective controls (group I). The Bursa Fabricius weight and its index were also markedly enhanced in the group II compared to the other groups. The weights of the other organs (abdominal fat, heart and gizzard) as well as serum total cholesterol and protein concentrations were not significantly altered by L carnitine supplementation and/or by the dietary energy level. These results suggest that, except a putative positive effect on humoral immunity, L carnitine did not provide significant effects on growth performance in young broilers even if the dietary energy level was weakly lowered. Keywords : Broiler, carnitine, growth, carcass trait, albumin, ration, energy level. RÉSUMÉ Effets de l addition de L-Carnitine dans des rations faiblement ou normalement énergétiques sur la croissance et les caractéristiques des carcasses chez le poulet. L objectif de cette étude était de déterminer les effets de l incorporation dans la ration de L carnitine sur la croissance, la composition des carcasses et sur quelques paramètres sériques (concentrations en cholestérol total, en protéines totales et en albumine) en fonction du niveau énergétique de la ration chez le poulet. 288 poussins ROSS 308 de 1 jour ont été répartis en 4 groupes égaux (n = 72) : les oiseaux des groupes I et II ont reçu une ration peu énergétique respectivement supplémentée ou non par la L carnitine (100 mg/kg d aliment) tandis que les 2 autres groupes ont bénéficié d une ration normalement énergétique supplémentée (group IV) ou non (groupe III) en L carnitine. Les poids des carcasses et leurs index pondéraux ont été significativement plus faibles chez les oiseaux recevant une ration peu énergétique. Les taux de mortalité et les paramètres de croissance (poids vifs, gain de poids, consommation alimentaire et efficacité alimentaire) n ont pas significativement varié entre les groupes bien que la supplémentation en L carnitine ait semblé légèrement améliorer la croissance des animaux recevant une ration faiblement énergétique (groupe II). Cependant, la L carnitine a induit une augmentation significative des poids des foies et de l albuminémie dans ce groupe par rapport aux contrôles correspondants (groupe I). Le poids moyen de la bourse de Fabricius ainsi que l index pondéral correspondant ont également été fortement augmentés dans ce groupe comparé aux autres groupes. Les poids des autres organes (graisse abdominale, gésier et cœur) ainsi que la cholestérolémie et l albuminémie n ont pas été significativement affectées par la supplémentation en L carnitine et/ou le niveau énergétique de la ration. Ces résultats suggèrent que, hormis un possible effet positif sur l immunité humorale, la L carnitine ne produirait pas d effets significatifs sur la croissance des jeunes poulets même si le niveau énergétique de la ration est faiblement réduit. Mots-clés : Poulet, carnitine, ration, niveau énergétique, croissance, carcasse, albumine. Introduction L-Carnitine has gained interest in the recent years as a potential food additive for improving domestic animal production and also as a substance with possibly ergogenic properties for increasing physical performance [25]. L-Carnitine (β-oh- ϒ-N-trimethylamino-butyrate) is a water-soluble quaternary amine. It is synthesized endogenously from the 2 essential amino acids, lysine and methionine [1, 6], and in normal physiological and nutritional conditions, L-Carnitine requirements are largely covered by dietary sources. The major metabolic role of L-Carnitine appears to be the transport of long-chain fatty acids into the mitochondria for β-oxidation [7]. Thus, dietary L-Carnitine supplementation could improve fatty acid and energy utilization and therefore gain and food efficiency, especially in young animal where synthesis is insufficient to meet endogenous requirements [11]. As broiler diets contain a high percentage of cereals which have very low L-Carnitine levels [4], insufficient endogenous L-Carnitine synthesis together with a low dietary carnitine supply could become limiting for metabolic requirements in case of increased metabolic demands. This insufficiency of L-Carnitine could lead to fatter animal [7].

2 292 ÇAKIR (S.) and YALÇIN (S.) Several studies have been conducted to determine whether dietary L-Carnitine may influence the broiler performances. BARKER and SELL [3] and LEIBETSEDER [12] failed to observe any effect of L-Carnitine supplementation on broiler performance, whereas other studies reported that L-Carnitine supplementation increased body-weight gain, reduced carcass fat and improved food conversion in pigs [24] and in broilers [19, 20]. The availability of L-Carnitine may become a limiting factor for fat oxidation when energy demands are elevated. In these circumstances, additional exogenous L-Carnitine might prove beneficial effect. The aims of the present experiment are to increase metabolic rate by decreasing diet energy, and to determine the effects of dietary L-Carnitine supplementation to diet with LE (low energy) or NE (normal energy) levels on growth performance, carcass composition, and some blood parameters. Materials and Methods ANIMALS AND EXPERIMENTAL PROTOCOL A total of 288 one day old ROSS 308 broiler chicks were obtained from a commercial hatchery and equally divided into 4 experimental groups (n=72) with 4 replicates of 18 birds per replicate. Diets were formulated to supply low energy (LE) (2800 and 3000 kcal/kg metabolisable energy, for starter and finisher diet respectively) or normal energy level (NE) (3000 and 3200 kcal/kg metabolisable energy, for starter and finisher diet respectively). Nutrients levels of the diets for broilers were based on the National Research Council [16] (Table I). The L-Carnitine content of the basal diets was calculated according to the L-Carnitine amount of the ingredients used [4]. The basal starter and the finisher diets with LE and NE contained 10.86, 10.74, and mg/kg L-Carnitine, respectively. Non supplemented LE and NE diets were given to control birds (groups I and III respectively) whereas the assay groups received L-Carnitine (100 mg/kg of food) supplemented LE and NE diet (groups II and IV respectively). Food and water were offered ad libitum to animals. Temperature in poultry house was maintained at 34 C for the first 5 days and then gradually reduced according to normal management practices, until a temperature of 23 C. A photoperiod of 23 light and 1 h dark was used. The trial was terminated 6 weeks later. Ingredient (%) Starter diets Finisher diets Low energy Normal energy Low energy Normal energy Corn Wheat Barley Soybean meal Full-fat soybean Fish meal Oil Limestone Dicalcium phosphate Common salt Vitamin premix Mineral premix Methionine Lysine Calculated analysis Metabolisable energy (kcal/kg) Crude protein (%) Lysine (%) Methionine (%) Ca (%) P (%) Linoleic acid (%) Carnitine (mg/kg) Provides per kg : IU vitamin A, IU vitamin D3, 30 g vitamin K3, 2 g vitamin B1, 5 g vitamin B2, 40 g niacin, 12 g panthotenic acid, 5 g vitamin B6 0,015 g vitamin B12, 0,75 g folic acid, 0,05 g biotin, 50 g vitamin C. 2 Provides per kg : 160 g Mn, 120 g Fe, 120 g Zn, 10 g Cu, 0,4 g Co, 2 g I, 0,3 g Se TABLE 1: Chemical composition of experimental diets given to broilers.

3 EFFECTS OF L CARNITINE AND DIETARY ENERGY LEVEL ON GROWTH OF BROILERS 293 PARAMETERS OF GROWTH PERFORMANCE AND BIO- CHEMICAL ANALYSES Mortality was recorded daily. At weekly intervals, broilers were weighed individually, and food intake and food conversion ratios (FCR) (kg food intake / kg body weight gain) were determined. Blood samples of 5 ml were obtained from each bird by Vena Subcutanea ulnaris puncture, allowed to clotting at room temperature for 6 hours and then centrifuged at g for 10 minutes. Serum total cholesterol, total protein and albumin concentrations were analyzed by the photometer (Merck Microlab 200, Netherlands, Serial No: ), using the commercial kits (Randox, United Kingdom). At the end of the trial, 16 broilers per group were individually weighed just prior to slaughtering for determining absolute and proportional weights of cold carcass, abdominal fat, liver, heart, gizzard and Bursa Fabricius. Chickens were slaughtered by severing the jugular vein. STATISTICAL ANALYSIS All data were analyzed by ANOVA using SPSS program (Inc., Chiago, II, USA). Significant differences among treatment were determined using Duncan s multiple range tests [8] with a 5 % level of probability. Effects of dietary treatments on mortality were evaluated using chi-square test. Results No significant difference was observed among the groups for mortality rates ranged from 1.33 % (group III: NE diet) to 4.0 % (group I: LE diet). Body weights (BW) and BW gains are presented in Table II. The final BW (obtained when birds were 42 day old) and cumulative BW gains appeared to be lower in broilers fed with L-Carnitine supplemented or not LE diets than in those fed with NE diets. However, differences between groups were not statistically significant. Furthermore, L-Carnitine supplementation had no significant effect on the weight growth (group I vs. group II and group III vs. group IV: not significant), even if final BW and cumulative BW gains of birds receiving L-Carnitine supplemented LE diets were improved by 4.3 % compared to the corresponding control. In the same way, when 2 periods of growth were considered (period 1: day 1 - day 21; period 2: day 22 - day 42), intermediate body weights and weight gains tended to be higher in birds fed with normal energy diets, and L carnitine supplementation tended to improve weight growth in birds receiving LE diets but no significant differences were evidenced between groups. Addition of L-Carnitine to the diets did not significantly influence periodic or cumulative food intake (Table II). Chickens fed with supplemented LE diet consumed more food Growth parameters Low energy diet Normal energy diet I (-C) II (+C) III (-C) IV (+C) P Body weights (BW) (g) At 14 days 244 ± ± ± ± 39 NS At 28 days 874 ± ± ± ± 145 NS At 42 days 1691 ± ± ± ± 285 NS BW gains (g) 1-21 days 481 ± ± ± ± 14 NS days 1175 ± ± ± ± 146 NS cumulative: 1-42 days 1655 ± ± ± ± 134 NS Food intake (g) 1-21 days 796 ± ± ± ± 40 NS days 2451 ± ± ± ± 67 NS cumulative: 1-42 days 3247 ± ± ± ± 94 NS Food Conversion Ratio (g/g) 1-21 days 1.66 ± ± ± ± 0.06 NS days 2.11 ± ± ± ± 0.21 NS cumulative: 1-42 days 1.97 ± ± ± ± 0.15 NS TABLE 2: Intermediate and final body weight (BW), body weight gain (BW gain), food intake and FCR in broilers receiving LE (low energy) and NE (normal energy) diets supplemented by L-Carnitine (C) (100 mg/kg food) (groups II and IV respectively) or not (groups I and III respectively). Results are expressed as means ± standard deviations. and showed a 2.6 % increase of cumulative food intake compared to the non supplemented controls, but the difference was not significant. On the other hand, food intake appeared to be lowered (-3.4 %) in the group IV (NE + carnitine diet) compared to the respective control (group III) but, again, this effect was not statistically significant. Furthermore, any significant effect of dietary energy level on food intake was evidenced. In the same way, cumulative FCRs did not significantly differ between groups even if this parameter appeared enhanced in birds receiving non supplemented LE diet (group I) and decreased in supplemented birds, particularly those of the group II.

4 294 ÇAKIR (S.) and YALÇIN (S.) The highest carcass weights (Table III) were obtained in birds fed with NE diets (groups III and IV) (p<0.05). Whereas differences of carcass weights between L-carnitine supplemented or non supplemented birds receiving the same dietary energy level were not significant, the carcass yield was significantly increased (p<0.05) in birds of the group IV (NE + carnitine diet) compared to the other groups. Carcass traits Low energy diet Normal energy diet I (-C) II (+C) III (-C) IV (+C) P Carcass Weight (g) 1286 ± 169 b 1334 ± 146 b 1490 ± 222 a 1429 ± 187 ab < 0.05 Index (%: carcass / slaughter weight) 70.0 ± 2.0 b 68.9 ± 3.7 b 71.4 ± 3.1 a 73.8 ± 6.6 a < 0.05 Gizzard Weight (g) ± ± ± ± 5.30 NS Index (%) 2.01 ± ± ± ± 0.28 NS Liver Weight (g) ± 7.80 b ± 4.80 a ± 8.90 a ± 6.10 a < 0.01 Index (%) 1.97 ± ± ± ± 0.44 NS Heart Weight (g) 8.75 ± ± ± ± 1.50 NS Index (%) 0.48 ± ± ± ± 0.15 NS Abdominal fat Weight (g) 17.0 ± ± ± ± 5.3 NS Index (%) 0.96 ± ± ± ± 0.25 NS Bursa Fabricius Weight (g) 2.47 ± 1.32 b 4.13 ± 1.20 a 3.07 ± 1.75 b 3.07 ± 1.22 b < 0.05 Index (%) 0.14 ± 0.10 b 0.21 ± 0.06 a 0.15 ± 0.09 b 0.16 ± 0.06 b < 0.05 Means on the same line with different superscript differ significantly. TABLE 3: Mean absolute (g) and proportional (%: g/100 g BW) organ weights in 42 day old broilers receiving LE (low energy) and NE (normal energy) diets supplemented by L-Carnitine (C) (100 mg/kg food) (groups II and IV respectively) or not (groups I and III respectively). Results are expressed as means ± standard deviations. In birds fed with supplemented or not NE diet (groups III and IV), the proportion of the gizzard weight appeared to be weakly but not significantly depressed compared to the groups I and II. By contrast, supplementation with L-Carnitine of LE diet (group II) has provided significant increase of absolute liver weight (p<0.01). Nevertheless, the proportions of liver and heart weights were similar in the different groups although the liver and heart weight indexes tended to be altered in the groups I and III respectively. Although the differences were not significant, the absolute heart weights were increased in L-Carnitine supplemented birds receiving LE and NE diets by 7.9 % and 5.0 % respectively. Interestingly, the lowest proportion of the abdominal fat was obtained in the group III (non supplemented NE diet) but the difference with the other groups was not significant. On the other hand, birds from the group II (supplemented LE diet) presented a marked increase of the Bursa Fabricius weight and of the corresponding index (p<0.05) compared to the other groups. While serum total cholesterol and total protein concentrations were identical in all groups, significant increases of the albumin concentrations (p<0.05) were evidenced in birds receiving supplemented LE diets (group II) compared to non supplemented birds (group I) (Table IV). Serum parameters Low energy diet Normal energy diet I (-C) II (+C) III (-C) IV (+C) Total cholesterol (mmol/l) 87.3 ± ± ± ± 39.4 NS Total protein (g/l) 25.3 ± ± ± ± 3.7 NS Albumin (g/l) 11.8 ± 3.0 b 15.7 ± 6.1 a 13.3 ± 1.5 ab 13.4 ± 1.6 ab < 0.05 Means on the same line with different superscript differ significantly. TABLE 4: Serum total cholesterol and proteins concentrations in 42 day old broiler receiving LE (low energy) and NE (normal energy) diets supplemented by L-Carnitine (C) (100 mg/kg food) (groups II and IV respectively) or not (groups I and III respectively). Results are expressed as means ± standard deviations. P

5 EFFECTS OF L CARNITINE AND DIETARY ENERGY LEVEL ON GROWTH OF BROILERS 295 Discussion In the present study, the effects of L carnitine dietary supplementation on growth parameters and weights of carcass and various organs of broiler chickens differ according to the energy level of the ration. Although differences were nor statistically significant between groups, L carnitine seemed to increase body weights, weight gains, food intake and the carcass weights when chickens received an energy-depressed diet, whereas these parameters tended to diminish in supplemented birds receiving a recommended dietary energy level. Free carnitine contents are low in tissues from neonatal chickens [21], and exogenous L-Carnitine supplementation during this critical period might be beneficial. Positive effects of the L-Carnitine supplementation were reported in broilers in some recent studies [19, 20]. These effects could be probably due to the increased requirement of L carnitine during this period due to a rapid growth. Studies with layers, young pigs and fishes have also shown some favourable responses to dietary L-Carnitine supplementation [22, 24]. Normally, feeding the birds with LE diet provides an increase of the food intake [9]. Some studies have shown some favourable effects of the dietary carnitine on food intake and FCR: supplementation with L-Carnitine at 0 to 1000 mg/kg starter diet to young pigs induced a dose-dependent improvement in food efficiency [17]. Other several studies [3, 13, 18] reported similar results for food intake and FCR in poultry. BAYRAM and AKINCI [5] detected a decrease of food intake and of FCR in quails about 7.84 and 8.91 % respectively by supplementation of 500 mg/kg diet with L-Carnitine. However, in most other studies with broilers [2, 3, 13] addition of L-Carnitine to the diet had no significant effect on growth rate, food conversion ratio and on the abdominal fat content. The exact reasons for the discrepancies between these studies are speculative but they might have been due to different levels of L-Carnitine supplementation, age at which L-Carnitine is added to diet, sex and broiler genotype, chick weight or basal diet composition. In the present study, although gizzard and liver weight indexes were not statistically modified, a relative hypertrophy of some organs (gizzard, liver and Bursa Fabricius) was observed in supplemented birds feeding with an energy-depressed ration, suggesting an enhancement of metabolism capacity of these tissues. It is not exactly clear how carnitine dietary supplementation can induce the increase of the Bursa Fabricius weight. L- Carnitine was recently reported to improve immune functions in broiler chickens [15]. Detailed evaluations of immunological parameters will be required for confirming immune positive effects of L carnitine in broilers, and particularly the relation between serum specific Ig titres and Bursa Fabricius weight. Albeit not extensively studied, the observed variations of the gizzard weight were in agreement with a previous study [18]. The significant increase of the liver weight in broilers receiving a low energy diet supplemented with L carnitine is rather surprising. Indeed, because L carnitine is known to promote mitochondrial fatty acid degradation, the fatty acid synthesis would be depressed, leading to the probable reduction of this organ weight and to a constant acetyl-coenzyme A production and a consequent increase of cholesterol biosynthesis. In this way, the liver weight appeared to be weaker in supplemented birds feeding with a normal energy diet compared to the respective controls and cholesterolemia tended to increase in parallel. Nevertheless, apparent conflicted effects of L carnitine on cholesterol concentrations were previously reported [14], the administration of L carnitine to hyperlipidemic fat-loaded rats inducing a marked reduction of cholesterolemia. In this case, the intense degradation of fatty acids promoted by L carnitine induced a massive release of acetylcoenzyme A residues which contributed with cholesterol excess to down-regulate the cholesterol synthesis. Consequently, the model presented by MACCARI et al. [14] was not comparable to the present study, in which birds were not hyperlipidemic. Measurements of serum triglyceride, HDL, LDL, VLDL and some long-chain fatty acids concentrations could be more relevant than cholesterol concentration to evaluate some effects of L-Carnitine on lipid metabolism. On the other hand, serum albumin concentrations were significantly increased by L carnitine supplementation in birds receiving low energy diet but not in birds receiving normal energy diet, suggesting that the albumin synthesis or an albumin sparing effect was induced by the food additive. Similarly, UYSAL et al. [23] detected in quails that 500 mg/kg diet L-Carnitine caused a significant increase of serum albumin concentration but decrease of total protein concentration. It would be also probable that the increase of the liver weight in the group of supplemented birds feeding with an energy-depressed ration was due to hyperplasia and not to fat deposits in liver. Histological examinations would be required for clarifying this point. The tendency of the heart weight hypertrophy in supplemented birds would be related to cardiovascular adaptive mechanism to the increased afflux and utilisation of fatty acids into cardiomyocytes triggered by L carnitine. Nevertheless, any effect of L carnitine on heart weight was reported in previous studies [18, 20]. Because L-Carnitine could play a major role in the regulation of the fat deposition in body [10], by acting on transport of long-chain fatty acids from cytosol into the mitochondria where the β-oxidation of these fatty acids occurs, L carnitine supplementation would induce a decrease of the abdominal fat weight. This fact was previously confirmed in broilers [19] and in young pigs [24]. However, other authors failed to obtain a significant reduction of abdominal fat content in geese but they have observed significant modifications of the proportions of saturated and polyunsaturated fatty acids in the abdominal fat [2]. In the present study, no significant alteration of the abdominal fat weight was evidenced in supplemented broilers: it was probable that the dietary energy level was not sufficiently lowered or that the duration of the experiment was not enough long for significantly throwing off balance of lipid metabolism and consequently for observing potential effects of L carnitine.

6 296 ÇAKIR (S.) and YALÇIN (S.) In conclusion, with this experimental design, no beneficial effect of L-Carnitine supplementation on broiler performance characteristics could be clearly demonstrated. However, these results do not exclude the possibility that L-Carnitine supplementation may be beneficial in other circumstances. Future evaluations with greater dietary concentrations of carnitine on growing broilers or with more depressed energy diet may be more relevant for investigating positive L-Carnitine effects. References 1. - ARSLAN C.: L-Carnitine and its use as feed additive in poultry feeding: a review, Rev. Med. Vet., 2006, 157, ARSLAN C., CITIL M., SAATCI M.: Effects of L- Carnitine administration on growth performance, carcass traits, serum lipids and abdominal fatty acid compositions of geese, Rev. Med. Vet., 2004, 155, BARKER D.L., SELL J.L.: Dietary Carnitine did not influence performance and carcass composition of broiler chickens and young turkeys fed low- or high-fat diet. Poult. Sci., 1994, 73, BAUMGARTNER M., BLUM R.: Foods without animal meal: Is adequate L-Carnitine provision still safeguarded LONZA Ltd. Technical Report. August, BAYRAM I., AKINCI H Z.: Uysal Japon bıldırcın (Coturnix coturnix japonica) rasyonlarına katılan L-karnitin ve C vitamininin besi performansı ve yumurta verimi üzerine etkisi. YYÜ Vet. Fak. Derg., 1999, 10, BREMER J.: Carnitine-metabolism and functions. Physiol. Rev., 1983, 63, BUYSE J., JANSSENS G.P., DECUYPERE E.: The effects of dietary L-Carnitine supplementation on the performance, organ weights and circulating hormone and metabolite concentrations of broiler chickens reared under a normal or low temperature schedule. Br. Poult. Sci., 2001, 42, DUNCAN D.B.: Multiple range and multiple F test. Biometrics., 1955, 11, ERGÜN A.: Tavuk Besleme. In: (A. ERGÜN, S.D. TUNCER Eds) Hayvan Besleme ve Beslenme hastalıkları, 2004, Pozitif Matbaacılık. Ankara GRIFFIN H.D., WHITEHEAD C.C.: Plasma lipoprotein concentration as an indicator of fatness in broiler development and use of a simple assay for plasma very low density lipoprotein. Br. Poult. Sci., 1982, 25, GROPP J.M., SCHUMACHER A., SCHWEIGERT F.J.: Recent research in vitamin nutrition with special emphasis to vitamin A, β-carotene and L-Carnitine. In: proceedings of the Arkansas Nutrition Conference. pp Fayetteville, AR: Arkansas Poultry Federation, LEIBETSEDER J.: Untersuchungen über die Wirkungen von L-Carnitin beim Huhn. Arch. Anim. Nutr., 1995, 48, LIEN, T.F., HORNG Y.M.: The effect of dietary L-Carnitine on the growth performance, serum components, carcass traits and enzyme activities in relation to fatty acid beta oxidation of broiler chickens. Br. Poult. Sci., 2001, 42, MACCARI F., ARSEN A., CHIODI P., RAMACCI M.T., ANGE- LUCCI L., HULSMANN W.C.: L-Carnitine effect on plasma lipoproteins of hyperlipidemic fat-loaded rats. Lipids, 1987, 22, MAST J., BUYSE J., GODDEERIS B.M.: Dietary L-carnitine supplementation increases antigen-specific immunoglobulin G production in broiler chickens. Br. Poult. Sci., 2000, 83, NATIONAL RESEARCH COUNCIL. : Nutrient Requirements of Poultry. 9th review edition. National Academy Press. Washington, OWEN K.Q., NELSSEN J.L., GOODBAND R.D., WEEDEN T.L., BLUM S.A.: Effect of L-Carnitine and soybean oil on growth performance and body composition of early-weaned pigs. J. Anim. Sci., 1996, 74, ÖZÇELIK H., YALÇIN S.: Broyler rasyonlarında L-karnitin ve humat kullanımı. Ankara Üniversitesi Vet. Fak. Derg., 2004, 51, RABIE M.H., SZILAGYI M., GIPPERT T.: Effects of dietary L-Carnitine supplementation and protein level on performance and degree of meatness and fatness of broilers. Acta Biol. Hung., 1997, 48, RABIE M.H., SZILAGYI M.: Effects of L-Carnitine supplementation of diets differing in energy levels on performance, abdominal fat content, and yield and composition of edible meat of broilers. Br. J. Nutr., 1998, 80, RINAUDO M.T., CURTO M., BRUNO R., PICCININI M., MA- RINO C.: Acid soluble, short chain esterified and free carnitine in the liver, heart, muscle, and brain of pre and post hatched chicks. Internat. J. Biochem., 1991, 23, TORREELE E., SLUISZEN A.V.D., VERRETH J.: The effect of dietary L-Carnitine on the growth performance in fingerlings of the African catfish (Clarias Garipinus) in relation to dietary lipid. Br. J. Nutr., 1993, 69, UYSAL H., BAYRAM I., DENIZ A., ALTINTA A.: L-karnitin ve vitamin C'nin Japon bıldırcınlarında bazı kan parametreleri üzerine etkisi. Ankara Üniversitesi Vet. Fak. Derg., 1999, 46, WEEDEN T.L., NELSSEN J.L., HANSEN J.A., FITZNER G.E., GOODBAND R.D.: The effect of L-Carnitine on starter pig performance and carcass composition. J. Anim. Sci., 1991, 69, 105 (Abstract) ZEYNER A., HARMEYER J.: Metabolic functions of L-Carnitine and its effects as food additive in horses. A review. Arch. Anim. Nutr., 1999, 52,