Effect of Slow-release Bolus of Zinc, Selenium and Cobalt on Some Blood Metabolites and Performance of Male and Female Mehraban Lambs

Zinc (Zn) is cofactor of more than 300 enzymes and is needed for growth, DNA synthesis, immunity and other important cellular processes (Wood, 2000). Cobalt (Co) has been demonstrated to be an essential nutrient for ruminants and is required by ruminal microorganisms for the synthesis of vitamin B12 (McDowell, 2000). Selenium is an integral component of the enzyme glutathione peroxidase (GSH-Px) which neutralizes the effects of hydrogen peroxide and lipid hydroperoxide (Awadeh et al, 1998). Trace element deficiencies occur most frequently in the grazing animal where the use of extra food is limited. Supplementation of these grazing ruminants with trace elements can prove difficulties. Trace elements can be supplemented in different ways. For example, the free-access methods (minerals, licks and blocks), but this suffers from variable intakes (Kendall, 1977). Oral drenches require frequent dosing in order to prevent deficiencies due to the short acting response of this type of supplement (Kendall et al., 2000). Injections require long term storage within the animal or frequent dosing. The controlled release bolus route should provide each animal with a consistent dose in line with its requirements sustained over a long period of time, such that one treatment of the animals should ensure adequate trace element cover for a number of months. The objective of our study was to determine the effects of slow-release bolus (Zn, Se and Co) on some blood metabolites and performance of male and female Mehraban lambs. To conduct this experiment, 20 male and 20 female Mehraban lambs with average body weight of 30.37±1.71 kg grazing on the waste of agricultural land were used in a completely randomized design as 2×2 factorial experiment for 70 days. Treatments consisted of: 1) control male lambs not receiving slow-release bolus; 2) control female lambs not receiving slow-release bolus; 3) male lambs receiving a slow-release bolus; and 4) female lambs receiving a slow-release bolus. Final body weight, average daily gain, zinc, selenium, copper, iron, vitamin B12 concentrations of plasma, serum alkaline phosphatase activity, GSH-Px activity in whole blood and concentrations of serum T3, T4 and ratio of T3 to T4 were determined on days 35 and 70. Data collected for different parameters and determined in different days, were analyzed as repeated measures in a completely randomized design. The model used for analysis was: Yijkl = µ + Ai + Bj + ABij + Eaijl + Ebijkl Where µ is overall mean, Ai: effect of treatment i, Bj: effect of day, ABij: interaction effect of treatment × day, Eaijl: error A, Ebijkl: error B. Duncan’s multiple range tests was used for comparison of means, considering P ≤ 0.05 as the significant level. The MIXED procedure of SAS (SAS Institute, 2004) was used for analysis of data. The average final body weight, average daily gain, plasma concentrations of zinc and selenium, alkaline phosphatase and glutathione peroxidase activity, plasma concentrations of vitamin B12 in groups receiving slow-release bolus were significantly higher than the control group(P