Document Type : Research Articles
Authors
Department of Animal Science, Faculty of Agriculture, Urmia University, Urmia, Iran
Abstract
Introduction: Arginine, as a precursor of nitric oxide, one of the main vasodilators, plays a significant role in inhibiting the pathogenesis of ascites (Khajali et al., 2014). Adding arginine to the diet can increase endothelial nitric oxide synthase activity, subsequently increasing nitric oxide production and reducing hematocrit. By reducing blood viscosity and pulmonary vascular resistance, the right ventricle of the heart will require less force to pump blood to the organs (Delfani et al., 2023). One of the most important applications of arginine in the body is its use in the production of guanidinoacetic acid, which is a precursor for creatine synthesis in the body (DeGroot et al., 2018). Guanidinoacetic acid is produced during the transfer of the amidino group from the amino acid arginine to the amino acid glycine by the enzyme arginine-glycine amidinotransferase, along with the amino acid ornithine (Kodambashi Emami et al., 2017; Asiriwardhana and Bertolo, 2022). Guanidinoacetic acid is the only precursor of creatine in the bodies of vertebrates (Kodambashi Emami et al., 2017). Adding guanidinoacetic acid to the diet can conserve arginine by providing creatine, especially in young growing chicks that have a higher need for creatine for rapid muscle growth (Asiriwardhana and Bertolo, 2022). To ensure optimal growth performance and various physiological responses, sufficient amounts of arginine in the diet of birds are essential. However, the level of arginine required for optimal growth is not sufficient for the activity of macrophages and the pulmonary vascular epithelium to produce maximum nitric oxide (Khajali and Wideman, 2010). Despite the beneficial effects of arginine in reducing the incidence of pulmonary hypertension syndrome (Khajali and Wideman, 2010), arginine supplementation in the diet is costly. Using an alternative compound such as guanidinoacetic acid, due to its diverse effects and lower cost compared to creatine and arginine, is more desirable in the diet of broilers (Khajali and Lemme, 2020). Therefore, the aim of this study is to investigate the effects of replacing different levels of guanidinoacetic acid with arginine on performance, carcass characteristics, susceptibility to ascites, and some blood parameters of broilers reared under cold stress conditions.
Materials and Methods: A total of 200 male Ross 308 broiler chicks with an average weight of 42 ± 1.5 g were used. The chicks were individually weighed at 11 days of age and divided into 20 experimental units in such a way that there was no difference in the initial weight of the experimental units. The current study was conducted in a completely randomized design with 4 treatments, 5 replicates, and 10 chicks per replicate. The experimental period started at 12 days of age and lasted until 42 days of age. Body weight gain, feed intake, feed conversion ratio, and ascites-related mortality were measured throughout the entire period (12-42 days of age). On day 42, one chick from each replicate (five chicks from each treatment) was randomly selected and slaughtered. Carcass components including carcass, breast, leg, and internal organs including heart, gizzard, pancreas, proventriculus, bursa, abdominal fat, pancreas, spleen, duodenum, jejunum, and ileum were weighed and their ratios to live weight were calculated. Additionally, after removing the heart, the right ventricle was separated from the septum between the ventricles. After washing, the weight of the right ventricle and total ventricles was measured using a digital scale with an accuracy of 0.001 g to calculate the ascites index. On day 41, blood samples were taken from the wing vein of two chicks per replicate (10 chicks from each treatment). The blood samples were placed in tubes containing the anticoagulant heparin. A portion of the blood samples was centrifuged at 2500 RPM for 10 minutes to separate the plasma for measuring nitric oxide levels, and the remaining samples were sent to the laboratory for analysis of blood characteristics including partial pressure of oxygen, partial pressure of carbon dioxide, pH, hemoglobin concentration, percentage of red blood cells, and red blood cell count. All data were analyzed using the ANOVA option of the general linear model of SAS software. Significant differences between treatment means were determined by Tukey's multiple range test. Differences in means were regarded as significant at P < 0.05.
Results and Discussion: The results of this experiment showed that supplementation with 0.5% arginine or 0.18% guanidinoacetic acid significantly improved feed conversion ratio compared to the control group. In addition to its role in preserving arginine and glycine for other metabolic pathways, guanidinoacetic acid plays a crucial role in nitric oxide synthesis and improves energy efficiency through ATP production via the creatine-phosphocreatine shuttle (Khalil et al., 2021). Additionally, increasing the level of guanidinoacetic acid supplementation linearly increased breast muscle yield and decreased relative weights of the small intestine, duodenum, and ileum. Khajali and Wideman (2010) stated that increasing arginine availability resulting from adding guanidinoacetic acid to the diet promotes cell proliferation and protein synthesis, which plays an important role in improving carcass traits. Supplementing with 0.18% guanidinoacetic acid also led to reductions in relative heart weight and the ratio of right ventricle weight to total ventricles compared to the control group. Nitric oxide concentration also significantly increased with supplementation of 0.18% guanidinoacetic acid and 0.5% arginine compared to the control group. Arginine is an essential substrate for nitric oxide synthesis produced by endothelial cells lining blood vessels. Nitric oxide acts as a potent vasodilator, expanding smooth muscle cells of blood vessels and regulating or inhibiting the production of vasoconstrictors such as endothelin-1 and serotonin, thereby reducing pulmonary vascular resistance (Khajali et al., 2011; Delfani et al., 2023). Reduced synthesis and availability of nitric oxide are contributing factors to increased pulmonary hypertension (Fathima et al., 2024). Hypoxic vasoconstriction of pulmonary arteries can be alleviated by increasing the synthesis of nitric oxide, which acts as a vasodilator (Khajali et al., 2014).
Conclusion: Generally, the results of the current study indicate that guanidinoacetic acid can effectively substitute arginine in the diet of broiler chickens raised under cold stress conditions.
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