Effect of some antioxidant sources on reducing salinomycin toxicity in pullet chicks

Introduction: Coccidiosis is a serious problem in the poultry industry, and medication is required continuously. There are several approaches to the control of coccidiosis. Several drugs have been used in the control of coccidiosis. The ionophore antibiotics such as lasalocid, maduramicin, monensin, narasin, and salinomycin are extensively used in poultry feed for the prevention or treatment of coccidiosis induced by Eimeria species. Unfortunately, the toxic effects of ionophores cause concern because of their narrow safety margin. Ionophores’ toxicity could be probably due to oxidative damage. Therefore, it can be prevented by the supplementation of antioxidants in the diet. It has been reported that 60 or 120 mg/kg of salinomycin caused some pathological changes in the liver, heart, kidney, and muscles, such as degeneration or necrosis of these tissues. However, administration of salinomycin with vitamin E or selenium showed that vitamin E decreases the pathological changes.  The present study aimed to investigate the effects of salinomycin administration in combination with some natural antioxidants on reducing salinomycin toxicity in laying chickens.
Materials and methods: A total number of 400 day-old hy-line w36 chicks were used in a completely randomized design with five treatments and four replications for 35 days. Treatments were included: 1) control diet, 2) negative control diet containing 0.05% salinomycin sodium, 3) negative control + garlic powder (15 g/kg of diet), 4) negative control + selenium (450 mg/kg of diet) + vitamin E (2 g/kg of diet), and 5) negative control + zinc-methionine (160 mg/kg of diet). Body weight gain, feed intake, and body weight uniformity were measured weekly. Blood samples were taken to evaluate the levels of antioxidant enzymes, liver enzymes, electrolytes, and malondialdehyde levels at the end of the experimental period.
Results and discussion: The results showed that the salinomycin diet (T2) decreased body weight and feed intake compared with the control diet in the total experimental period (P<0.05). But the addition of supplemental Zn-methionine to the diet (T5) led to improved body weight and feed intake (P<0.05). Significant differences were observed among various treatments for the relative weight of visceral organs (liver, heart, kidney, gizzard, proventriculus, intestine, and bursa of Fabricius), but there were no significant differences for spleen and lungs. Also, salinomycin increased the activity of liver enzymes including alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and serum malondialdehyde (MDA) in the negative control group and control group, and decreased the level of serum antioxidant enzymes compared to the control group (P<0.05), but the addition of vitamin E + selenium to the diet, eliminated the negative effects of salinomycin on these parameters (P<0.05). Vitamin E plays important roles in various biochemical and physiological processes, including antioxidation. The protective effect of vitamin E against the alterations induced by salinomycin on these estimated parameters in this study could be attributed to the role of vitamin E as a fat-soluble antioxidant, which protects the biological membranes from oxidative damage and decreases osmotic fragility of erythrocytes. Selenium also exerts its protective effect against oxidative damage by a decline in free radicals and increasing the synthesis of glutathione peroxidase, which catalyze the breakdown of toxic hydrogen peroxide and lipid hydroperoxides. Salinomycin decreased serum chlorine and increased serum potassium compared to the control group (P<0.05), and only the use of vitamin E + selenium adjusted these changes (P<0.05). The T2 group reduced the serum level of chlorine and increased the serum level of potassium (P<0.05). But there is no significant effect on the level of blood calcium. Although all treatments with antioxidants changed the levels of these electrolytes. The changes in electrolyte balance can result in metabolic alkalosis and acidosis. However, the T4 group only reduced the serum levels of potassium and calcium and increased the serum level of chlorine significantly, compared to the T2 group (P<0.05). However, there were no significant differences in the serum sodium and creatinine levels among various treatments.
Conclusions: Salinomycin administration in the diet of laying chicken induces undesirable effects on some estimated parameters probably due to oxidative damage. But, the supplementation of pullet diets with vitamin E and selenium can reduce the possible side effects of salinomycin.