اثر سطوح مختلف اکسیدروی در جیره‌های حاوی سلنیت سدیم بر عملکرد رشد و برخی شاخص‌های ایمنی گوساله‌‌های شیرخوار هلشتاین

Abstract
Inroduction: Micro elements have a number of structural, catalytic and regulatory functions in organisms and play a major role in the functioning of the immune system. Trace mineral amount of colostrum and milk is not optimal, and dietary inclusion of trace mineral supplements is necessary for suckling calves. Selenium (Se) is an essential mineral for humans and livestock and has now been identified asan integral constituent of over 35 selenoproteins that function in enzymatic, structural or as yet unidentified roles. In livestock, Se is important for fertility and disease prevention. Sufficient Se increases fertility rate, improves antioxidant defense systems and immunological potential. Selenium deficiency in cattle is associated with several problems, including delayed conception, muscular degenerative disease in calves, myocardial necrosis and heart failure, immune dysfunction, increased risk of mastitis, abortion and perinatal mortality, and growth retardation in young animals. Recommendation of National Research Council (NRC 2001), the daily requirements of selenium and vitamin E for growing calves are 0.30 mg and 40 IU, respectively. Selenium plays a role in the defence against the accumulation of hydroperoxides from cellular metabolism. This biological function is accomplished through the selenoproteins, such as the glutathione peroxidase family (GPx) the iodothyronine deiodinases and the thioredoxin reductases, in which selenium is a structural component. Selenium also functions at the active site of enzymesinvolved in the production and regulation of thyroid hormones and isrecogn ized for itsrole in immune function. To prevent Se deficiency and promote animal health, inorganic Se sources (sodium selenite and selenate) are commonly used to supplement livestock diets.
Zinc is associated with more than 300 enzymes either as component or as activator. Zinc involved in immunity, metabolism, growth and reproductive functions. Zinc plays a role in the structure and activity of antioxidant enzymes. The role of Zn as an antioxidant and its importance for cell replication and proliferation are the two most direct connections between Zn and the immune function. Because of mineral interaction, inorganic forms have lower bioavailability in the gastrointestinal tract.
Therefore, the objective of this study was to assess the effect of sodium selenite and zinc oxide oxide supplementation on from two levels on growth performance, immune response ,blood parameters and antioxidant status of Holstein calves.
Materials and methods: The calves were housed in a well ventilated sheds with cement floors having provision for individual feeding and watering. A basal diet was prepared using locally available feed ingredients to meet the nutrient requirements of calves growing (NRC, 2001) except for Zn and Se. The ingredients and chemical composition of basal diet was given in Table 1. Calves fed milk based on 10% of body weight in the morning and evening. The experiment was started at 4 days of age and calves were kept up to 42 days in individual hutches. For this study, 36 Holstein calves with 34.5±2 kg gavarage weight in a completely randomized design for 42 days were used. The basal diet (containing 40 mg zinc and 0.15 mg selenium) was without zinc and selenium supplementation (diet 1). Diet 2 contained 0.3 mg sodium selenite, diet 3 contained 40 mg zinc oxide, diet 4 contained 55 mg zinc oxide, diet 5 contained 0.3 mg sodium selenite + 40 mg zinc oxide, and diet 6 contained 0.3 mg sodium selenite + 55 mg zinc oxide. Feed intake was calculated daily, and calves were weighed weekly to calculate the feed conversion ratio (FCR) and average daily gain. Blood samples were collected on days 20 and 42 to determine the plasma trace mineral levels and biochemical, enzymatic, hormonal, antioxidant, and hematological parameters. growth performance and Blood parameters data were analyzed using the PROC GLM procedure of SAS. Significance among treatments was determined by the duncan test and results were considered as significant the P-value was less than 0.05.
Results and discussion: The results showed that use of sodium selenite and different levels of Zinc oxide had no significant effect on feed intake, final weight, weight gain growth performance, immune response (P>0.05). no significant differences were observed between concentrations of blood metabolites )P>0.05(. whereas supplementing milk with 0.3 mg sodium selenite and 40 and 55 mg Zinc oxide significantly increased the activity of superoxide dismutase and reduced levels of malondialdehyde and aspartate aminotransferase (P<0.05). In summary supplementing milk with composition Zinc oxide and sodium selenite improve the antioxidant status and help to cope with the stress.