| This research was conducted to investigate the effects of a novel organic selenium (Se) source-selenomethionine (Se-Met) and its different forms on growth performance, feed utilization and meat quality in broilers, and approached to the mechanism of effects by Se deposition, antioxidant ability, immunity, hormone level, key metabolism enzymes activities and selenoprotein gene expression, consequently to provide a theoretical basis for the industrialization and scientific application of Se-Met. Five experiments were conducted in this paper.Experiment 1 was conducted in a 2×4 factorial arrangement in a randomized complete block design to investigate the effects of DL-Se-Met on broilers and its optimum supplemented level, sodium selenite (SS) served as control. A total of 840 7-day-old Straight-run Ross 308 broilers with an average body weight of 162±0.59 g were randomLy allotted to seven treatments, each of which included three replicates of 40 birds. There were a control diet containing 0.04 mg Se/kg and six additional diets that included 0.05,0.15,0.25 mg Se/kg from SS or DL-Se-Met. The experiment lasted 42 days. Feed and water were provided ad libitum throughout the experiment. At 49 days of age, four male broilers per replicate were randomLy selected based on the similar body weight for slaμghter experiment, and serum, liver, kidney, pancreas and breast muscle were sampled for laboratory analysis. The resμlts showed that:(1) DL-Se-Met coμld act as an effective Se source in broilers, and the optimum supplemented level was 0.15 mg Se/kg.(2) Compared with SS, DL-Se-Met significantly increased the feed utilization (P < 0.05). The Hunter a value of breast muscle at 16 h was increased and the drip loss of breast muscle at 24 and 48 h was reduced by DL-Se-Met supplementation in comparison with SS supplementation (P< 0.05). The Se concentration in serum and organs was significantly higher in the DL-Se-Met-treated group than that in the SS-treated group (P< 0.05). DL-Se-Met supplementation significantly increased total antioxidation capability (T-AOC) and glutathione (GSH) content in serum and tissues, superoxide dismutase (SOD) activity in breast muscle, while decreased malondialdehyde (MDA) content in tissues and glutathione peroxidase (GPx) activity in breast muscle and pancreas, compared with broilers fed SS diet (P< 0.05). The thymus index and serum IgG, IgA, IgM contents were greatly improved by DL-Se-Met in comparison with SS (P< 0.05). The addition of DL-Se-Met significantly increased TT3 concentration and decreased the ratio of TT4 to TT3 (P< 0.05), when compared with broilers fed SS diet.Experiment 2 was conducted to compare the effects of different forms of Se-Met on broilers, SS served as control. A total of 8001-day-old Straight-run Ross 308 broilers with an average body weight of 44.30±0.49 g were randomLy allotted to four treatments, each of which included five replicates of 40 birds. These four groups received the same basal diet containing 0.04 mg Se/kg, supplemented with 0.15 mg Se/kg from SS, L-Se-Met, D-Se-Met or DL-Se-Met. The experiment lasted 42 days. Feed and water were provided ad libitum throμghout the experiment. At 42 days of age, four male broilers per replicate were randomLy selected based on the similar body weight for slaμghter experiment, and serum, liver, kidney, pancreas and breast muscle were sampled for laboratory analysis. The resμlts showed that:(1) Average daily gain, average daily feed intake and feed conversion ratio were not affected by the dietary treatments in any period of growth or in the overall data (P>0.05).(2) Se-Met groups were more effective in decreasing drip loss of breast muscle at 24 and 48 h after slaμghter and depositing Se in serum and different organs studied than SS group (P< 0.05).(3) The antioxidant status was greatly improved in broilers of DL-and L-Se-Met-treated groups in comparision with the SS-treated group and was illuminated by the increased GSH concent in serum and liver, T-AOC in pancreas and breast muscle and decreased MDA concent in tissues of broilers (P< 0.05). Besides, supplementation with D-Se-Met was more effective in increasing serum GSH concent and decreasing breast muscle MDA concent than SS (P< 0.05). When compared with broilers fed SS diet, supplemental DL-and L-Se-Met significantly increased serum IgG content and trypsinase activity (P< 0.05). The TT3 concentration was increased and the ratio of TT4 to TT3 was reduced by DL-and L-Se-Met compared with SS (P< 0.05). The SS supplemented diet increased more cellμlar glutathione peroxidase (GPxl) and thioredoxin reductase 1 (TrxRl) activities in liver and kidney as well as selenoprotein P (SelP) content in serum and liver than the D-Se-Met supplemented diet (P< 0.05). In addition, liver and kidney TrxRl activities were significantly decreased by DL-and L-Se-Met in comparison with SS (P< 0.05).(4) Compared with L-Se-Met, DL-Se-Met significantly increased T-AOC in pancreas, GSH, IgA and IgG contents in serum, Se concentration in serum, kidney and breast muscle, while decreased MDA content in liver (P< 0.05). GPx1 activity and GSH content in liver, T-AOC in pancreas and breast muscle as well as amylase and trypsinase activites in pancreas were significantly decreased by D-Se-Met supplementation in comparison with L-and DL-Se-Met supplementation (P< 0.05).(5) In the aspects of GPx1> TrxR1,Se1P and selenoprotein W (SelW) relative mRNA level, DL-Se-Met was superior to D-Se-Met (P< 0.05); D-Se-Met was superior to L-Se-Met (P< 0.05); L-Se-Met was superior to SS (P< 0.05).(6) Partial cDNA sequence of chicken GPx1 gene was first successfμlly cloned by using RT-PCR method, the sequence was 416 bp.Experiment 3 was conducted to study the antioxidant ability of different forms of Se-Met in vitro by primary cultured kidney cell of chicken embryo, SS served as control. The resμlts showed that:(1) The T-AOC, GSH content and SOD activity were greatly improved and MDA content was notably decreased in broilers fed Se-Met compared with those in broilers fed SS (P< 0.05); while GPx activity was significantly decreased by DL-and L-Se-Met in comparison with SS (P< 0.05).(2) Compared with D-Se-Met, L-and DL-Se-Met significantly increased SOD and GPx activities, T-AOC and decreased MDA content (P< 0.05); GSH content in DL-Se-Met group was significantly higher than that in L-Se-Met group (P< 0.05).Experiment 4 was conducted to investigate the effects of different hydrogen peroxide (H2O2) contentrations and exposed time on relative cell viability and lactate dehydrogenase activity in medium of cultured chicken embryo kidney cell. The resμlts showed that oxidative stress of kidney cells of chicken embryo coμld be induced, when they were treated with 100μmol/L H2O2 for 12 h.Experiment 5 was conducted in a 4×7+1 factorial design to investigate the anti-oxidative stress effects of SS and different Se-Met forms on kidney cells damaged by H2O2. The resμIts showed that:Oxidative stress decreased the antioxidant status of kidney cells, GPx activity, T-AOC and GSH content decreased, while MDA content increased (P< 0.05); Se-Met and SS supplementation coμld attenuate H2O2-induced stress injury in kidney cells, but when compared with the normal control group, DL-and L-Se-Met coμId restore the activities of antioxidants to the normal level, while D-Se-Met significantly decreased GPx activity and T-AOC (P< 0.05), SS significantly decreased SOD activity, T-AOC and GSH content as well as increased MDA content (P< 0.05). In addition, DL-Se-Met increased more GSH content than L-Se-Met (P< 0.05); D-Se-Met supplementation significantly increased T-AOC, GSH content and increased MDA content compared with SS (P< 0.05).The resμlts of this study indicated:(1) Se-Met coμld act as effective organic sources of Se supplementation of feed mixtures for broilers, and the optimum supplemented level was 0.15 mg Se/kg for DL-Se-Met; (2) DL-and L-Se-Met had higher nutrient-biological effects than SS in the aspects of meat quality, Se deposition, antioxidant ability, immunity, hormone level and key metabolism enzymes activities; while D-Se-Met possessed higher nutrient-biological effects than SS in the aspects of meat quality, Se deposition and antioxidant ability; (3) With respect to antioxidant ability, the tendency was that:Se-Met was superior to SS, while DL-Se-Met> L-Se-Met> D-Se-Met. |
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