| Three experiments were conducted in the present study to determine the effects of pres-laughter oxidative stress on meat quality and the regulations of dietary selenium and vitaminE on oxidative stress in broiler by injection of dexamethasone (DEX) in order to provide abeneficial accumulation to establish the technology of nutrient regulation against stress inbroiler industry.In trial one, effects of preslaughter oxidative stress on meat quality of broilers were in-vestigated. Twenty-four broiler chickens (Cobb500,39-day-old) with near-mean body weight(BW) were randomly divided into three following treatments: sham injection of saline (con-trol), daily subcutaneous (s.c.) injection of DEX (3mg/kg or6mg/kg of BW, respectively)for3days. The results showed that average daily feed intake and BW of chickens were sig-nificantly decreased in the DEX treatment (P<0.05), it was the same as the change of thedressing percentage and leg muscle rate, however, the variation of breast muscle rate was notsignificant difference(P>0.05). The DEX treatment significantly decreased the pH at24hoursafter slaughter of breast muscle (P<0.05), simultaneously, significantly increased the redness(a*) and water-loss rate of breast muscle (P<0.05), but had no significant influence on shearforce of breast muscle (P>0.05). The pH at45minutes,24hours after slaughter of thigh mus-cle were significantly dropped in the DEX treatment(P<0.01), while the shear force of thighmuscle was significantly augmented(P<0.05), the change of water-loss rate of thigh musclewas not significant difference (P>0.05).The plasma,breast muscle and thigh muscle MDAwere signigicantly enhanced in the DEX treatment (P<0.05), simultaneously,the plasma activ-ity of glutathione peroxidase(GSH-Px),total antioxidant capacity(T-AOC) levels and activityof catalase(CAT) were signigicantly increased(P<0.05). Our reaearch results suggested thatthe body anti-oxidative systerm could be activated when broilers exposed to oxidative stress.Although such response could be useful to prevent oxidative injury, the following sequenceresulted in decreasing growth performance and meat quality.In trail two, effects of dietary selenium and vitamin E on growth performance,meat qual-ity,immunity and oxidation resistance in broiler chickens exposed to DEX-induced oxidativestress was evaluated. A total of200one-day-old broiler chicks (Cobb500) were randomly di- vided into four treatments with5replicates of10birds. The first treatment was fed acorn–soybean meal basal diet, while the residual treatments were fed the basal diet supple-mented with selenium0.2mg/kg, vitamin E200mg/kg, or selenium0.2mg/kg＋vitamin E200mg/kg, respectively. All the treatments were randomly divided into two groups (A, B) at16days of age. Subsequently, the group B was injected at abdomen s.c. with DEX (3mg/kgBW) for3times every other day, while the group A was injected with saline and served ascontrol. The results were as follows:(1)The average daily feed intake and BW gain were significantly suppressed (P<0.01)during DEX injection (16~21days), while the DEX treatment had no significant influence ongrowth performance in22~42days (P>0.05).(2)The DEX treatment had no significant impact on slaughter parameters of42-day-oldbroilers (P>0.05).(3)At21days of age, the pH at45minutes,24hours after slaughter of thigh muscle weresignificantly dropped in the DEX treatment compared with control (P<0.05).At the same timethere was significant interaction of selenium,vitamin E and DEX treatments for pH at45mi-nutes after slaughter (P<0.05).However,the DEX treatment had no significant influence onlightness(L*), redness(a*) and yellowness(b*)(P>0.05).In addition,the water-loss rate ofbreast muscle was significantly enhanced in the DEX treatment (P<0.05).At42days of age,the variation of pH,color,shear force and water-loss rate of breast muscle were not significantdifference among the treatments (P>0.05).(4)The DEX treatment signigicantly decreased the thymus index and bursa of fabriciusindex of21-day-old broilers (P<0.01).There was significant interaction of vitamin E and DEXtreatment on bursa of fabricius index of21-day-old broilers (P<0.05).In contrast,the DEXtreatment had no significant influence on immue organ index of42-day-old broilers(P>0.05).Furthermore, the vitamin E (P<0.01) and DEX (P<0.05) treatment significantlyaugmented the serum immunoglobulin A(IgA) of21-day-old broilers.However,the DEXtreatment had no significant effect on newcastle disease antibody level of35-day-old and42-day-old broilers(P>0.05).Dietary selenium and vitamin E significantly enhanced the new-castle disease antibody level of35-day-old broilers (P<0.05).(5)At21days of age,the DEX treatment significantly increased the plasma MDA levels(P<0.05), activity of GSH-Px(P<0.01) and bursa of fabricius activity of GSH-Px(P<0.01).Dietary vitamin E significantly declined the breast and bursa of fabricius MDA le-vels (P<0.01) and enhanced plasma T-AOC levels (P<0.05).Dietary selenium significantlyincreased plasma activity of CAT and decreased breast muscle MDA levels (P<0.05).At42days of age,there was no significant influence on plasma and breast muscle MDA le- vels,T-AOC levels and activity of GSH-Px (P>0.05).These results suggested that growth performance, meat quality and immunity were sig-nificantly declined when broilers suffered from acute oxidative stress induced by DEX.Moreover, dietary supplementation with selenium and vitamin E during early growth andacute oxidative stress stage could not completely eliminate the injuries of oxidative stress forbroilers.However, dietary supplementation with selenium and vitamin E was favorable forimproving immunity and oxidation resisitance to alleviate DEX-induced oxidative stress, alsocontributed to chickens retrieve from stress state to the normal.In trail three, effects of oxidative stress on DNA damage, DNA methylation and themodulation by vitamin E were evaluated. A total of100one-day-old broiler chicks (Cobb500)were randomly and equally assigned to two treatments with5replicates.The birds were fedeither a basal diet or a basal diet supplemented with vitamin E (200mg/kg basal diet). All thetreatments were randomly divided into two groups (A,B) at16days of age. Subsequently, thegroup B was injected at abdomen s.c. with DEX (3mg/kg BW) for3times every other day,while the group A was injected with saline and served as control. The results indicated that thegrowth performance was significantly suppressd when birds exposed to DEX-induced oxida-tive stress (P<0.01).8-hydroxydeoxyguanosine (8-OHdG) concentration enhanced by DEXtreatment (P<0.05), while activity of DNA demethylase declined (P<0.05).Dietary vitamin Esignificantly augmented average daily feed intake and daily gain (P<0.05) and tended to atte-nuate8-OHdG concentration (P>0.05).However, the activity of DNA demethylase was notinfluenced by vitamin E supplementation (P>0.05). The results of current research suggestthat broilers had a poor performance under oxidative stress through increasing degree of DNAdamage or DNA methylation. Supplemented with vitamin E was useful to improve the growthperformance and alleviate DNA oxidative injury to some extent, whereas no significant effecton DNA methylation was observed. |
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