اثر استفاده از ال-کارنیتین در جیره‌های حاوی روغن ماهی بر عملکرد، پارامترهای آنتی‌اکسیدانی و فراسنجه‌های لیپیدی سرم و زرده تخم‌مرغ در مرغ‌های تخم‌گذار

Introduction: Oils have multiple effects, including improved palatability, increased feed intake, safety, and performance (Stovanovic et al., 2018). Compared to broilers, the amount of oil added to the diet of laying hens is lower because laying hens have a unique physiological status and are more susceptible to lipid metabolism disorders than broilers (Gao et al., 2021). Omega-3 fatty acids play an important role in human nutrition due to their reduced incidence of cardiovascular and inflammatory diseases (Roohanipour et al., 2022). Fish oil is one of the main sources of omega-3 polyunsaturated fatty acids, especially long-chain ones. The fatty acid profile of this oil shows that more than 30% of its fatty acids are omega-3 polyunsaturated fatty acids (Kartal et al., 2003). However, products containing higher proportions of omega-3 fatty acids make them more susceptible to lipid peroxidation, which is an undesirable characteristic (Bassels et al., 2000). The fatty acid profile of the oil plays a role in the susceptibility of oils to oxidation, as unsaturated fatty acids, and especially unsaturated fatty acids with multiple double bonds, are more susceptible to lipid peroxidation than saturated fatty acids (Weissman et al., 1998). Therefore, the use of antioxidants in diets containing fish oil seems to be crucial. Recently, the antioxidant role of L-carnitine has also been considered. L-carnitine is reported to be a potent antioxidant that reduces oxidative damage while enhancing antioxidant enzyme activity, thus protecting cells from damage (Mansouri et al., 2024). In recent years, although fish oil has been used to enrich eggs with omega-3 fatty acids and even its positive effects on egg-laying physiology, its storage and oxidation problems have always been a matter of debate. Therefore, the present study was conducted to investigate the effect of L-carnitine supplementation in diets containing different levels of fish oil on the antioxidant function and parameters of blood and liver, and serum and egg yolk lipid parameters in aged laying hens.
Materials and methods: In this study, 432 laying hens (Hy-line-W36, 65 weeks of age) were used. Birds with similar body weight (1530 ± 50 g) were selected and allocated in a 3 × 3 factorial design with 6 replications and 8 birds per replication. In order to adapt to the experimental conditions, the birds were first fed with the basal diet for 2 weeks and then with the experimental treatments for 8 weeks (56 days). The experimental treatments included diets containing 3 levels of fish oil (0, 1.5 and 3% of the diet) and 3 levels of L-carnitine (0, 300 and 600 mg/kg of the diet), which were adjusted according to the nutritional recommendations of the Hy-line-W36 strain in 2020. To evaluate performance indicators, eggs were collected twice a day (10 am and 4 pm) and the number and total weight of eggs were recorded at the end of each day. Egg mass, feed intake and feed conversion ratio were calculated weekly. To evaluate blood parameters, two serum samples from each replicate (12 samples per treatment) were prepared at the end of the experimental period. To evaluate the antioxidant status of the liver, at the end of the experimental period, 6 chickens from each treatment were slaughtered and after opening the carcass, the livers of the birds were separated and sent to the laboratory to evaluate the antioxidant status. To measure yolk lipids, 100 mg of egg yolk was mixed with 2.5 ml of NaOH solution using a digital scale and neutralized with 2.5 ml of HCl solution (after 24 hours). The samples (liver, yolk and serum) were tested using an automatic analyzer and kits prepared from Pars Azmoun Company. Serum lipids were measured at a wavelength of 550 nm based on the enzymatic method and serum and liver antioxidant parameters were measured based on the methods recommended by the kit manufacturer. All data from this experiment were statistically analyzed in the form of a 3x3 factorial test using SAS software and the Mixed procedure.
Results and discussion: The results showed that hens treated with 3% fish oil and 300 and 600 mg L-carnitine had the highest percentage of production, weight and egg mass, which was significantly higher than the treatment without fish oil and L-carnitine. The feed conversion ratio also increased in the treatments without L-carnitine supplementation compared to the other experimental treatments (P<0.05). Diets containing 1.5 and 3% fish oil caused a decrease in the total antioxidant capacity of the liver and serum and an increase in serum malondialdehyde, which the use of 300 and 600 mg L-carnitine in these diets increased the total antioxidant capacity and reduced malondialdehyde. Also, the main effects of fish oil and L-carnitine showed that 3% fish oil increased liver malondialdehyde levels and 300 and 600 mg L-carnitine increased the activities of superoxide dismutase and glutathione peroxidase enzymes compared to the control treatment (P<0.05). The interaction of L-carnitine and fish oil had synergistic effects on serum triglyceride, cholesterol, and LDL concentrations, and 1.5 and 3% fish oil levels along with 300 and 600 mg L-carnitine significantly reduced serum triglyceride, cholesterol, and LDL concentrations. The main effects of L-carnitine at 300 and 600 mg L-carnitine levels decreased yolk cholesterol concentrations and increased serum HDL (P<0.05).
Conclusion: In general, according to the results obtained, the present researchers recommend using 1.5 and 3% fish oil in the diet of laying hens in order to benefit from the positive effects of fish oil on egg-laying performance and blood lipid parameters. However, based on the present results, if 3% fish oil is used, the use of L-carnitine can be beneficial to prevent lipid peroxidation and reduce yolk cholesterol.