عنوان مقاله [English]
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.