چكيده لاتين :
Introduction: 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.
Materials and Methods: 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.
Results and Discussion: 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 <0.05). Serum tri-iodothyronine (T3) amount increased (P <0.05), while serum thyroxine (T4) amount decreased (P <0.05). Serum ratio of T4/T3 in in groups receiving slow-release bolus was significantly lower (P <0.05) than that of the control group. Glutathione peroxidase activity, the average final weight and average daily gain of male’s lambs were higher than those of female lambs (P <0.05). Copper and iron concentrations in plasma of male and female lambs were not affected by treatment (P >0.05). Similar to our findings, supplementation of 65 mg Zn/kg DM in the basal diet (15 mg Zn/kg DM) in female (Chhabra and Arora, 1985) and male (Chhabra and Arora, 1993) goats significantly increased serum Zn concentration. Kendall et al., (1997 and 2012) indicated that administration a slow-release bolus (Zn, Co and Se) to sheep was increased plasma Zn concentration in bloused animals than control group. Changes in the rate of plasma ALP tend to reflect changes in concentration of Zn in plasma among animals (Kirchgessner, 1980; Vergnes et al., 1990). It is reported that ALP activity increases at higher levels of Zn supplementation (Wan et al., 1993; Kraus et al., 1997; Nagalakshmi et al. 2009). It seems that the level of Zn was not sufficient for adequate ALP activity in lambs and the administration of a slow-release bolus (Zn, Co and Se) improved ALP activity. Selenium deficiency has been shown to reduce the activity of deiodinase in liver (Beckett et al. 1992). Similar to our findings in growing male calves (Arthur et al. 1988), heifers (Wichtel et al. 1996) and suckling calves, selenium supplementation increased plasma concentration of T3 and decreased T4. Higher concentration of T3 in bolus receiving lambs in our study shows that deiodinase activity was improved by selenium supplementation. The only known animal requirement for cobalt is as a constituent of vitamin B12, which has 4% cobalt in its chemical structure. This means that a cobalt deficiency is really a vitamin B12 deficiency (Berger, 2006). Microorganisms in the rumen are able to synthesize vitamin B12 needs of ruminants if the diet is adequate in cobalt. Normally, cobalt is not stored in the body in significant quantities. Zervas et al. (1988) indicated that administration a slow-release bolus (Cu, Co and Se) at 3 month prepartum to ewes increased the plasma concentrations of vitamin B12 until three months postpartum.
Conclusion: Overall results showed that slow-release bolus can meet the requirements of male and female lambs for the above mentioned trace elements and increase their performance. This result indicated that higher performance of bolus receiving group can be related to continuous release of Zn, Se and Co from the bolus.
