اثرات پیش‌مخلوط مواد معدنی بر عملکرد، پر درآوری، خصوصیات استخوان درشت‌نی و میزان تجمیع عناصر معدنی در سرم و پر جوجه‌های گوشتی

Introduction:
 In commercial production, there is often concern about the quantity and/or quality of feathering in both broilers and layers. For broilers, the concern is adequacy of protective feather cover, while in layers usually the necessary degree of feathering needed to optimize feed efficiency. Feather development is under the control of hormones such as thyroxine and estrogen and indirectly by testosterone. Therefore, environmental or nutritional status affecting the hormonal output of the birds will indirectly influence their feathering. Nutrition influences rate of feathering as well as feather structure, color and molting. In spite of the fact that minerals constitute a little proportion of body weight (2 to 5%) in vertebrates, their significance is high for growth, enzyme activation, immune system, regulation of the osmotic pressure, egg production and feathering. Urine and blood serum or plasma are the most commonly used bio fluids for metabolomics-based studies for the simple reasons that they both contain hundreds to thousands of detectable metabolites. In blood, the minerals undergo homeostatic controls, thus the ranges of concentrations are narrow, but the concentration of minerals in hair and feather is broad and can reflect long term metabolic changes. Blood tests can vary significantly depending upon animal’s diet, activity level, the time of day and many other factors. Contrary to the blood, the concentration of minerals in hair and feather is broad and can reflect long term metabolic changes. Hair or feather can be considered as a metabolically inactive tissue, and its composition indicates the levels of trace elements that store in its structure through nutritive blood flow. Feather chemistry has been investigated as a means of identifying the geographic origins of migrating and wintering populations of birds, and as an indicator of environmental pollution. Since the minerals are crucial to the functioning of enzymes, hormones and other biochemical systems, it is possible to read the hair or feather test and see where metabolic patterns are deviating from the norm. The present study was amid to examine the potential applicability of serum or feather samples as a biological indicator to evaluate the broiler responses to (un)sufficient diets with regards to the trace mineral supplementation at 0, 25, 50, 75 and 100% of the recommended requirements.
 
Material and Methods:
 A total of 200 one-day-old Ross 308 strain of broiler chicks (male and female) were used in a completely randomized design with 4 replicates of 10 chicks each. A large batch of corn and soybean meal basal diet was prepared for each age period (0-14, 14-35 and 35-42 days) and aliquots used for mixing the experimental diets. The experimental diets were prepared by mixing mineral premix at 100, 70, 50, 25, and 0% of normal inclusion rates, resulting in five experimental diets. At the end of the experiment, two male chicks close to average weight of each experimental unit were selected for bone quality assessment and feathering scores for wing and tail using scores of 1 to 5 for feather coverage with 1 representing minimal coverage, i.e. <25% coverage; 2 for 25-50% coverage; 3 for 50-75% coverage; 4 for >75% coverage and 5 for complete coverage. The wing and tail were further evaluated on a scale of 0 to 2 for the occurrence and severity of poor feathering with 0 indicating no defect; 1 for lesion and torn feathers, and 2 indicating blisters had developed on the shaft, near failure of feather to emerge from the follicle, broken feathers and retarded feathering. Tibia bone morphometric parameters, i.e. weight, diameter, length, density, volume and ash, were determined. The serum mineral concentration was measured in the fasting state at the end of the experiment. At this time, a total of 3mL of the blood samples was accumulated in plain vacutainer tubes from the veins under the wing. After collecting, the blood samples were left undisturbed for at least 1 hour to reach the room temperature. The serums were centrifuging at 3,000 rpm for 15 minutes. The obtained sera were kept in 1.5mL micro tubes at -80°C until they were analyzed for mineral concentration. The method of American Society for Testing and Materials, D4638–03 standard, was used for preparing the serum and feather samples.
 
Results and Discussion:
 The results showed that treatments supplemented with mineral premix caused increase in average daily gain and feed intake compared to the control group (P<0.05), but the difference among mineral premix-supplemented groups was not significant (P>0.05). Feed conversion ratio in the starter period was not affected by the experimental treatments; nevertheless, in the growing and finishing periods a significant difference was indicated compared to the control. Bone parameters including weight, diameter, length and volume showed significant differences to the control group; but the difference for density and ash were not significant. Effects of dietary trace mineral supplementation on the feathering scores of broilers were described.. The results showed that the effect of trace mineral supplementation was significant for feather coverage and defect feather in both wing and tail regions (P<0.05). Feathering score was increased and the amount of damaged feathers was reduced in concordance with the increase in mineral supplementation. Serum concentration of Ca increased in response to trace mineral supplementation. Feather K (p<0.01) and Zn (p<0.05) concentrations were affected by the dietary treatments. Serum concentration of Zn increased linearly in proportion to the dose of Zn supplementation when 10, 25 or 40 mg/kg Zn were added to the basal diet. The diagnostic usefulness of feather analysis is confirmed by authors who have proven the correlation between the concentration of basic elements in feather and their concentrations in the body both in the physiological and pathological states. With regard to the use of feather as a nondestructive monitoring tool, it is noticeable that it presented inter-tissue correlation with the serum in most occasions.
Conclusion: Feather could be considered as an appropriate criterion to diagnose the mineral status in the body.