اثر بلوس آهسته‌رهش حاوی روی، سلنیوم، مس، کبالت، منگنز و ید بر عملکرد رشد و فراسنجه‌های خونی بره‌های نر مهربان

Introduction:
Trace minerals are essential for supporting growth and health of animals. Trace element deficiencies are common in many countries and affect animal health, productivity and welfare. Trace elements imbalance conditions may be manifested as a consequence of a single or a multiple elements deficiency. The trace elements; selenium, copper, zinc, manganese, iodine and cobalt have been shown to be involved in immune function of domestic farm animals and will therefore potentially have roles in the etiology of infectious diseases of these species (kendall et al, 2012). In addition, many structural proteins, enzymes and cellular proteins rely on the presence of these minerals to function properly (spears et al, 2004). Among them, we can mention the activation of enzymes, strengthening the immune system and improving performance (Aliarabi et al., 2017).
Zinc is essential for the metabolism of carbohydrates, proteins and nucleic acids (Hosnedlova et al., 2007). Selenium is part of the glutathione peroxidase enzyme, which plays an important role in protecting the cell membrane and oxidative processes. In addition, selenium plays an important role in the protection of the thyroid gland as well as the metabolism of thyroid hormones, and selenium deficiency causes the destruction of mitochondrial and cell membranes (Awadeh et al., 1998). Copper is essential for growth and prevention of pathological and clinical problems in animals (Underwood and Suttle, 1999). Copper deficiency can cause anemia, bone disorders, connective tissue disorders, insufficient growth of lambs, and abortion (Thompson et al., 1994). Manganese is an essential element in bone growth, reproduction and improving the functioning of the nervous and immune system (Harley, 1981). Cobalt is another essential element that is underutilized in ruminants. Cobalt is part of vitamin B12 and plays a role in protein and energy metabolism (Kadim et al., 2003). The most important task of iodine in the body is the synthesis of thyroid hormones, which leads to goiter (Zimmerman et al., 2006). Using supplemental feed as a trace element carrier incurs the costs of both feed and labour, if additional feed is not required. Free access minerals, mineral licks and blocks are subject to variable intakes with animals consuming between nothing and many times the required intake. daily supplementation has a short-term effect and is impractical for systems such as grazing that manual feeding is not possible (Masters and White, 1996). Methods such as injection, which provide specific doses at regular intervals, are suitable for elements with storage capability in the body, but injection is also an expensive and time-consuming practice. Oral dosing with trace element drenches is another possible alternative. Although this ensures that each animal receives a dose, it may need regular handling, storage mechanisms for the element and/or a high animal tolerance to the levels of element given for long term dosing (Kendall et al, 2001). The use of slow-release boluses can provide a certain amount of minerals to the animal over time. It has been reported that the use of slow-release bolus containing copper, cobalt and selenium has improved the performance of sheep compared to the control group (Kendall et al., 2012).
The aim of this trial was to determine the effect of slow-release bolus containing zinc, selenium, copper, cobalt, manganese and iodine (multitace) on the performance and blood parameters of Mehraban male lambs.

Materials and methods: 14 Mehraban male lambs aged 5.5 months with an average weight 29±2kg were used in a completely randomized design in two treatments and seven replicates. The control group received basal diet and the bolus treatment received basal diet + slow release bolus. The slow-release boluses used in this study was made in accordance with the method of Fadayifar and Aliarabi (2013), and contained 150000ppm Zn, 2282.5ppm Se, 21600ppm Cu, 2574ppm Co, 20250ppm Mn and 2125ppm I and released 150 to 200 mg daily on average. Bolus was administered on day 0 prior to feeding via a bolus gun. The duration of the experiment was 56 days. To obtain the amount of feed consumed (based on dry matter), daily feed consumption and its residue were measured. Lambs were weighed in the first days of the experiment and days 14, 28, 42 and 56 of experiment in order to determine weight changes and performance of lambs. blood sample were taken on first and last day of the experiment before the morning meal. Alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), mineral elements concentration (zinc, copper, iron, calcium and phosphorus), total protein, albumin, globulin and blood urea nitrogen concentrations were measured. Data were analyzed in a completely randomized design using GLM procedure of SAS 9.1 of software.

Results and discussion: Although the final weight and feed conversion ratio in the lambs receiving bolus showed a numerically higher than control, but statistically no significant difference was observed in the measured parameters. Blood parameters including liver enzymes activities, concentrations of total protein and globulin showed no significant difference between the treatments, but the blood serum albumin was significantly higher in lambs that received bolus than control (P<0.05). Plasma zinc concentration also increased significantly in the group receiving bolus compared to the control group (P<0.05).
Conclusion: In general, the use of slow-release bolus containing (zinc, selenium, copper, cobalt, manganese, iodine) had an effect on the concentration of albumin and zinc element, and a significant difference was observed in group receiving bolus and the control group. But it had no significant effect on the performance of lambs, liver enzymes activities and the concentration of other mineral elements and blood proteins parameters. According to the results, although the difference in performance was not significant, the daily weight gain of lambs receiving the bolus was about six percent higher than the control group, and this could improve efficiency.