Study the Effects of Different Levels of Fat and L-carnitine on Performance, Carcass Characteristics and Serum Composition of Broiler Chicks

MATERIALS AND METHODS

In a factorial arrangement with 3 levels of soy oil (1, 3, 5 %) and 2 levels of L-carnitine (0 and 250 mg kg ¹), three hundreds and sixty, one-day old Ross 308 male broiler chicks were randomly distributed in 24 pen with 15 chicks in each pens. This experiment was carried out in a local poultry farm in Mashhad in summer 2004. The chicks were kept in litter pens under uniform environmental condition from hatch until 6 week of age. Temperature was kept 32°C for the first week and reduced 3°C weekly thereafter. A continuous lighting program was provided during the experiment. Diets were formulated by using of UFFDA software. All diets were isocaloric and isonitrogenous. Prior to experimental diets formulation, feed ingredients were analyzed for their moisture, CP, EE, CF and ash (AOAC, 1984). The main ingredients in diets were corn, soybean meal and fish meal. Experimental diets were fed from 1 to 42 days of age. Starter and grower diets were fed from 1 to 21 and 21 to 42 days of age respectively. The ingredients percentage and chemical composition of in starter and grower periods are shown in Table 1. Feed and water were provided ad-libitum during the entire experimental period. During the experiment feed intake, body weight gain, feed conversion ratio were measured weekly. Mortality was measured throughout the experiment. In day 42, one chick from each pen, with body weight similar to pen average body weight, was selected and slaughtered to determine carcass, breast meat, abdominal fat, heart, liver weight and percentage. Feed and water were withdrawal 12 and 4 h respectively before slaughtering. For determination of TG, cholesterol, VLDL, glucose, LDL, HDL, 10 mL of blood were taken from wing vein of each bird in each unit. There were 6 (3 levels of fat and 2 levels of L-carnitine) treatments and 4 replicates with 15 chicks in each replicate. Data from this experiment were analyzed using the General Linear Model (GLM) procedure of SAS (SAS Institute, 1998). When differences among means were found, means were separated using Duncan's multiple ranges test at p<0.05 (Steel and Torrie, 1980).

Table 1:	Composition of diets used in starter (1-21 days) and grower period (22-42 days) (%)
1Supplied per kilogram of diet: 6050 µg vitamin A (retinyl acetate+retinyl palmitate), 55 µg vitamin D3, 22.05 µg vitamin E (dl- -topheryl acetate), 2.0 mg K3, 5 mg B1, 6.0 mg vitamin B2, 60 mg vitamin B3, 4 mg vitamin B6, 0.02 mg vitamin B12, 10.0 mg pantothenic acid, 6.0 mg folic acid, 0.15 mg biotin, 0.625 mg ethoxyquin. 2Suppled per kilogram of diet: 500 mg CaCO3, 80 mg Fe, 80 mg Zn, 80 mg Mn, 10 mg Cu, 0.8 mg I, 0.3 mg Se

RESULTS AND DISCUSSION

The effects of dietary fat supplementation at different levels on feed intake, body weight gain and Feed Conversion Ratio (FCR) of broiler chicks in starter, grower and whole periods of the experiment are summarized in Table 2 and 3. Effects of fat on feed intake was significant in all periods of the experiment (p<0.05). With increasing the level of fat in diets feed intake increased. Broiler fed with diets containing 5% fat consumed the most feed in all phases of the experiment. Supplemental fats increase the palatability of the diet and reduced the dustiness of the feed, thus the feed intake can be increased (Bisplinghoff, 1992; Wiseman and Salvdor, 1991). Addition of fat to diets increased body weight gain and improved FCR in grower and whole period of the experiment (p<0.05). Chicks fed with diets containing 3 or 5% fat had the most body weight gain and best value for FCR. There were not significant differences between treatments containing 3 and 5% fat for these traits and therefore, the optimum level of supplemental fat in broiler diets was 3% on basis of the situation of the present study. Diet fat per se can affect rate of passage of digesta and this can influence overall diet digestibility. Delay rate of passage suggests that digesta spends more time in contact with digestive enzymes, carriers or co-factors and absorptive sites, therefore addition of fat to the diet may increase digestion of non-fat components of the diets (Mateos and Sell, 1981; Sell et al., 1986). These findings are in agreement with results of previous studies (Lien and Horng, 2001; Xu et al., 2003). The effects of different levels of fat on carcass traits are shown in Table 4. Dietary fat also had significant effect on breast meat percentage and fat content of breast meat (p<0.05). Increasing the level of fat in diets from 1-3 or 5% improved breast meat yield (p<0.05). It may be related to increasing the fat content of breast meat. With increasing the level of fat from 1-3 or 5% in diets the fat content of breast meat significantly increased too (p<0.05). The results are in agreement with the findings of the other researchers (Ajuyah et al., 1991; Cortinase et al., 2004). Effect of dietary fat was significant on abdominal fat and liver weight percentage (p<0.05). There were significant differences between treatments containing 1 and 3% and between diets containing 3 and 5% fat for this trait. With increasing dietary fat, more energy was available for the chicks and it is stored in adipose tissues and as abdominal fat. The effects of L-carnitine supplementation at different levels on feed intake, gain and FCR of broiler chicks at different phases of the experiment are presented in Table 5. Adding L-carnitine to diets had not significant effect on feed intake, body weight gain and FCR in all phases of the experiment (p>0.05). These results are in agreement with findings of the previous studies (Leibetseder, 1995; Buyse et al., 2001). Cartwright (1986) reported that growth performance of broilers, in terms of body weight and feed intake, was not affected by feeding diet supplemented with 0.05% L-carnitine of the diet from 5 to 7 weeks of age. Barker and Sell (1994) also reported that the supplementation of dietary L-carnitine at 0, 50, or 100 mg kg ¹ diet did not affect body weight gain, feed intake, or feed efficiency of broiler chickens and young turkeys fed low- or high-fat diets. Likewise, Leibetseder (1995) pointed out that body weight gain and feed conversion ratio of broiler chickens were not influenced by dietary carnitine at 200 mg kg ¹. The dietary addition of 100 mg kg ¹ L-carnitine did not affect body weight gain, feed intake, or feed efficiency of broilers (Buyes et al., 2001). Lien and Horng (2001) noticed that feeding diets supplemented with 0 and 160 mg of L-carnitine kg ¹ did not significantly affect the performance of broiler chickens. Xu et al. (2003) observed no differences in body weight gain, feed intake, or FCR of from 20 to 60 mg kg ¹ tended to improve growth male broilers fed diet supplemented with 0, 25, 50, 75, or 100 mg kg ¹ L-carnitine.

Table 2:	Effect of different levels of fat on performance of broiler chicks in starter and grower periods
Means with different superscript(s) in each rows differ significantly (p<0.05)

Table 3:	Effect of different levels of fat on performance of broiler chicks in whole period (1-42 days) of the experiment
Means with different superscript(s) in each rows differ significantly (p<0.05)

Table 4:	Effect of different levels of fat on carcass characteristics of broiler chicks
Means with different superscript(s) in each rows differ significantly (p<0.05)

Table 5:	Effect of different levels of L-carnitine on performance of broiler chicks
Means with different superscript(s) in each rows differ significantly (p<0.05)

Table 6:	Effect of different levels of L-carnitine on carcass characteristics of broiler chicks

However, Lettner et al. (1992) showed that dietary supplementation with L-carnitine performance of broiler chickens. Rabie et al. (1997b) indicated that the supplementation of dietary L-carnitine at 3 levels (50, 100, or 150 mg kg ¹) to a basal diet significantly increased body weight gain of broiler chickens compared with those of broilers fed the basal diet. The discrepancies between studies may result from different levels of L-carnitine supplementation, ingredients and metabolizable energy, methionine and lysine levels of diets, sex and physiological status of the animals. The calculated methionine and lysine (the precursors of L-carnitine) levels in the present experimental diets were sufficient for broiler chicks according to the nutrient requirements established by the National Research Council (NRC, 1994)

The effects of different levels of L-carnitine on carcass traits of broiler chicks are shown in Table 6. Adding L-carnitine had not significant effect on breast meat yield and liver and heart weights. These findings are in agreement with results of other experiments (Barker and Sell, 1994; Leibetseder, 1995; Sarica et al. 2005; Deng et al., 2006). Likewise, Celik et al. (2003) indicated that supplementary carnitine did not influence carcass weight, carcass yield, or relative weight of abdominal fat in broiler chickens. Due to increasing the oxidation of fats, adding L-carnitine to diets trend to have a significant effect in lowering (1.32 vs 1.57%) abdominal fat (p<0.07). It also reduced the fat percentage of breast meat (1.07 vs 1.27%). The fat-lowering effect of dietary L-carnitine obtained in the present study may be explained, at least partly, by a reduction in hepatic lipogenic capacity, since liver is the major site of lipogenesis in poultry, but other factors may be also responsible for the regulation of the rate of fat accumulation in adipose tissue. This may imply that abdominal fat is the most susceptible component of a broiler carcass for alternation by dietary L-carnitine. Rabie and Szilagyi (1998) and Xu et al. (2003) reported that the abdominal fat percentage of body weight was significantly reduced by adding L-carnitine to diets. Conversely, other studies with poultry have been shown that abdominal fat did not affected by adding dietary L-carnitine (Barker and Sell, 1994; Cartwright, 1986). Cartwright (1986) observed no significant effect on abdominal fat when L-carnitine was fed at 0.05% of the diet from 5 to 7 weeks of age. Barker and Sell (1994) reported that addition of L-carnitine to the diet (50 or 100 mg kg ¹) did not influence abdominal fat weight of broiler chickens fed low- or high-fat diets. Leibetseder (1995) also reported that abdominal fat content of broilers was not affected by dietary carnitinet 200 mg kg ¹ of diet. Rabie et al. (1997a, b) pointed out that supplementary carnitine did not significantly affect live body weight or the relative weights of liver, heart and gizzard, except abdominal fat pad weights. Daskiran and Teeter (2001) observed no significant effect in dressing percentage and abdominal fat pad contents of broilers in response to dietary L-carnitine supplementation. Xu et al. (2003) showed that crude fat content in breast muscle of male broilers is significantly increased by supplementing with 50 or 75 mg of L-carnitine kg ¹ of diet. Interaction of different levels of fat and L-carnitine on feed intake, gain, FCR are summarized in Table 7.

Table 7:	Effect of different levels of fat and L-carnitine on performance of broiler chicks (1-42 days)
Means with different superscript(s) in each rows differ significantly (p<0.05)

Table 8:	Effect of different levels of fat and L-carnitine on carcass characteristics of broiler chicks (% live weight)
Means with different superscripts in each rows differ significantly (p<0.05)

Table 9:	Effect of different levels of fat and L-carnitine on blood serum composition of broiler chicks (mg dL 1)
Means with different superscript(s) in each rows differ significantly (p<0.05)

Interaction of fat and L-carnitine had not significant effect on above traits (p>0.05). Interaction of fat and L-carnitine on carcass traits are shown in . The levels of TG and glucose in blood serum were affected by increasing dietary fat. There was significant difference between treatments containing 3 and 5% fat for serum TG. Increasing the level of serum glucose in chicks fed with diets containing 5% fat probably related to glycerol content of TG, which converted to glucose via gluconeogenesis pathway. Adding L-carnitine to diets significantly decreased the level of serum TG, cholesterol and VLDL (p<0.05). Decreasing the level of serum TG in chicks fed with diets supplemented with L-carnitine probably related to increasing oxidation of fatty acids. With increasing the transportation capacity of fatty acids to inner mitochondrial membrane, the serum TG level was reduced. L-carnitine supplementation to diets containing high level of fat, increases oxidation of fatty acids and reduces the secretion of VLDL in liver, thus the level of serum VLDL reduces. The results are in agreement with the previous findings (Lien and Horng, 2001; Xu et al., 2003). Interaction of fat and L-carnitine on blood serum components are presented in Table 9. Interaction between fat and L-carnitine on serum TG and glucose wasm significant (p<0.05). In general use of 3% vegetable oil inn this experiment caused the best performance in male broiler chicks and under the condition of this experiment, adding 250 mg kg ¹ L-carnitine to broiler diets in some extend reduced abdominal fat percentage. The effectiveness of supplemental dietary L-carnitine for increasing performance and carcass characteristics may be depend on condition which L-carnitine is added. Results of the present experiment showed positive effect of fat on performance and the significant effect of L-carnitine on decreasing the levels of serum TG, cholesterol and VLDL. For future researches, use of L-carnitiune in broiler diets without rich sources of carnitine (fish meal) containing high level of fat and also with feed restriction status are recommended.