عملكرد و پاسخ به تنش انتقال بره هاي ماده بلوچي تغذيه شده با سطوح مازاد بر نياز مكمل هاي آلي كروم و سلنيوم

Performance and Physiological Response to Transportation Stress of Baluchi Ewe Lambs Fed Selenium-methionine and Chromium-methionine Supplements

به منظور بررسي اثرات تغذيه مكمل هاي آلي سلنيوم و كروم بر عملكرد و پاسخ بره به شرايط تنش انتقال، تعداد 24 راس بره ماده بلوچي در سن چهار ماهگي با ميانگين وزن اوليه0/4 ± 24/2 كيلوگرم در قالب يك طرح كاملا تصادفي به 4 تيمار با 6 تكرار اختصاص داده شدند. تيمارها شامل جيره پايه فاقد مكمل آلي سلنيوم و كروم (كنترل)، جيره پايه + 1/5 ميلي گرم در كيلوگرم مكمل آلي سلنومتيونين (گروه سلنيوم)، جيره پايه + 0/8 ميلي گرم در كيلوگرم مكمل آلي كروم متيونين (گروه كروم) و جيره پايه حاوي 1/5 ميلي گرم سلنومتيونين + 0/8 ميلي گرم كروم متيونين (گروه سلنيوم-كروم) بود. طول دوره پژوهش شامل 2 هفته سازگاري و 9 هفته آزمايش بود. در ابتداي هفته 8، آزمايش تنش انتقال به مدت 30 دقيقه انجام شد و خونگيري قبل و بعد از تنش انجام شد. نتايج آزمايش نشان داد كه تغذيه بره هاي ماده با مكمل هاي آلي سلنيوم و كروم سبب افزايش وزن زنده و بهبود ضريب تبديل غذايي شد (ضريب تبديل براي گروه هاي كنترل، سلنيوم، كروم و سلنيوم-كروم به ترتيب 5/99، 5/41، 5/22 و 5/45 بود). در بين تيمارها، بره هاي تغذيه شده با مكمل كروم-متيونين بيشترين مصرف خوراك روزانه و افزايش وزن زنده را نشان دادند. گروه تغذيه شده با مكمل كروم غلظت گلوكز كمتري نسبت به گروه كنترل داشت. پاسخ فيزيولوژيك بره ها در شرايط تنش انتقال حاكي از اثرات كاهش دهندگي غلظت كورتيزول و گلوكز مكمل هاي آلي سلنيوم و كروم بود. گروه تغذيه شده با مكمل كروم-متيونين غلظت گلوكز خون را بطور معني داري نسبت به گروه كنترل كاهش داد. بر اساس نتايج بدست آمده، استفاده از مكمل آلي كروم-متيونين و سلنيوم-متيونين مي تواند سبب بهبود عملكرد و كاهش اثرات نامطلوب تنش بر فراسنجه هاي خوني و عملكرد بره هاي ماده شود.

Introduction Most parts of Iran are located in arid and semi-arid areas which animals undergo feed shortage due to poor natural vegetation. Metabolic modifiers such as anabolic steroids, somatotropin, beta agonists, vitamins and minerals, fed in extra-nutritional levels, increase growth rate, feed efficiency, carcass leanness, profitability of livestock production and decrease carcass fatness. Moreover, heat and transportation stress results in decreased feed intake, body weight, average daily gain and reproductive performance of animals. Chromium (Cr) and selenium (Se) are micronutrients which could be considered as metabolic modifiers. It has been reported that dietary Se supplementation improves reproductive performance, oxidative stress, immune system, as well as growth performance of the animals. Cr supplement, as a constituent of low-molecular-weight Cr-binding substance (LMWCr) or chromodulin, also increases glucose tolerance by potentiating the action of insulin. However, there are a few information regarding the effects of organic Se and Cr supplements on performance and blood metabolites of ewe lambs under transportation stress. Thus this study aimed to evaluate the impacts of feeding selenium-methionine (Se-Met) and Chromium-methionine (Cr-Met) supplements on growth performance and blood metabolites of ewe lambs. Materials and Methods Twenty-four Baluchi ewe lambs with mean body weight of 24.2 ± 0.4 kg and 4 months old were allocated randomly to 4 dietary treatments including (1) control diet (no Se or Cr supplementation), and control diet supplemented with (2) Se-Met (1.5 mg kg-1 dry matter (DM)), (3) Cr-Met (0.8 mg kg-1DM) and (4) Se-Cr-Met (1.5 mg of Se-Met plus 0.8 mg of Cr-Met kg-1DM).The whole experimental period divided into two periods of adaptation (2 weeks) and data collection (9 weeks). A transportation stress was applied by transporting the animals in a truck in a bumpy road for 30 minutes in 8th week of the experiment. Blood samples were collected at commencement and the end of experiment. For transportation stress, blood samples were obtained just before the lambs were loaded and unloaded from the truck. Serum glucose, urea, creatinine, total protein and albumin concentrations were measured by spectrophotometer and cortisol by enzyme-linked immunosorbent assay (ELISA) method. Statistical analysis was carried out using SAS software. A mixed model with fixed effects of treatment, time and random effect of lamb within treatment × time were used. A paired T-test was used to compare the blood metabolite concentrations pre-transportation with post-transportation stress. Results and Discussion The results indicated that, feeding ewe lambs diets contained organic Se and Cr supplements improved average daily gain )ADG( and feed conversion ratio (FCR: control, Se, Cr, and Se-Cr were 5.99, 5.41, 5.22, 5.45 respectively). Lambs in Cr-Met group showed the highest feed intake and live weight gain compared those in the control. Blood glucose concentration decreased in Cr-Met fed lambs in comparison with control animals. Feeding Se-Met and/or Cr-Met supplements had no effect on blood urea, creatinine, cholesterol, total protein and albumin concentrations. Based on the findings, blood glucose and cortisol concentrations were increased in response to transportation stress. Feeding Cr reduced the concentration of blood cortisol. It seems that the beneficial effects of Cr are associated with its role in carbohydrate and protein metabolisms. Chromium potentiates insulin action by enhancing its binding to target cell receptors and also by improving its post-receptor signaling. Insulin increases protein synthesis, efficiency of amino acid transport, and carbohydrate and lipid utilization and reduces protein degradation. Selenium supplements also improve feed efficiency by increasing triiodothyronine activity and enhancing antioxidant status. Moreover, Cr can prevent the deleterious effects of transportation stress. Conclusion It could be concluded that feeding ewe lambs with organic selenium (0.8 mg kg-1) and chromium (1.5 mg kg-1) supplements may improve feed to gain ratio and ameliorate the changes in blood glucose and cortisol concentrations in response to transportation stress.