Effect Of Betaine On Lipid Metabolism,Meat Quality And Antioxidant Capacity In Broilers

Betaine is effective in reducing body fat deposition,improving carcass composition and meat quality,and enhancing antioxidantive ability of broilers.However,the mechanism for reducing body fat deposition and improving meat quality is still not clear and no information is available about the effect of betaine on redox state in broilers under heat stress.Therefore,the objective of study was conducted to investigate the effects of betaine on lipid metabolism,meat quality and redox state in broilers.The study was composed of 3 trials as below:Trial 1 was conducted to investigate effect of different levels of dietary betaine on lipid metabolism of broilers.A total of 240 1-day-old Arbor Acres broiler chickens with similar body weight(BW)were selected and randomly assigned to 5 dietary treatments with 6 replicates of 8 chickens per replicate cage.Broiler chickens were fed a basal diet supplemented with 0(control),250,500,750 or 1000 mg/kg betaine,respectively.The results showed that growth performance and serum biochemical values of broilers were not affected by betaine.Incremental levels of betaine decreased the absolute and relative weight of abdominal fat(linear P<0.05,quadratic P<0.01),low-density lipoprotein cholesterol(LDL-C),triglyceride(TG)and total cholesterol(TC)(linear P<0.05),and increased concentration of nonesterified fatty acid(NEFA)(linear P =0.038,quadratic P =0.003)in serum of broilers.Moreover,incremental levels of betaine increased linearly(P<0.05)the proliferator-activated receptor alpha(PPARa),the carnitine palmitoyl transferase-?(CPT-?)and 3-hydroxyacyl-CoA dehydrogenase(HADH)mRNA expression,but decreased linearly(P<0.05)the fatty acid synthase(FAS)and 3-hydroxyl-3-methylglutaryl-CoA(HMGR)mRNA expression in liver of broilers.Trial 2 was conducted to evaluate the effects of betaine on the carcass characteristics,breast meat quality and antioxidant capacity of broilers.The experimental design was the same with trial 1.The results showed that compared with the control,750 mg/kg betaine increased(P<0.05)breast muscle percentage of broiler.Incremental levels of betaine increased(linear P =0.001,quadratic P =0.044)crude protein content in breast muscle,but had no significant effect(P>0.05)on ether extract or moisture content in breast muscle.Incremental levels of betaine linearly decreased(P<0.05)drip loss at 48 h postmortem and tended to decrease(P<0.1)pressure loss,but had no effect on meat color,pH,cooking loss(P>0.05)of breast muscle.Moreover,incremental levels of betaine linearly increased(P<0.05)superoxide dismutase activity in breast muscle.Compared with control,betaine decreased(P<0.05)malondialdehyde content in breast muscle.Dietary supplementation with 750 mg/kg betaine increased(P<0.05)glutathione content in breast muscle and 250,500 mg/kg betaine supplementation tended to increase glutathione content in breast muscle compared with the control.Betaine had no effect on activity of GPX in breast muscle(P>0.05).Trial 3 was conducted to evaluate the effects of betaine on growth performance and redox state in broilers under heat stress(HS).A total of 144 21-day-old broiler chickens with similar body weight were assigned randomly to 3 treatments with 6 replicates of 8 chickens per replicate cage.The control broilers received a basal diet and raised at constant environmental temperature of 22 ± 1 ? until 42 days of age.Birds in the other two groups were fed a basal diet without(HS)or with 1000 mg/kg betaine(HS+BET)and raised at 34± 1 ? for 8 h from 9:00 to 17:00 and at 22 ± 1 ? at the rest of time until 42 days of age.The results indicated that compared with the control group,HS decreased average daily gain(ADG),average daily feed intake(ADFI),but increased(P<0.05)rectal temperature,cockscomb temperature and activities of aspartate aminotransferase(AST)and alanine aminotransferase(ALT)in serum and malondialdehyde(MDA)content in liver.In addition,HS decreased(P<0.05)activities of superoxide dismutase(SOD)and glutathione peroxidase(GPX)in both liver and hepatic mitochondria and catalase(CAT)activity,glutathione(GSH)content and GSH/glutathione disulphide(GSSG)ratio in liver of broilers.Betaine supplementation tended to increase(P<0.1)ADG and ADFI of broiler,but decreased(P<0.05)ALT activity in serum compared with HS.Moreover,betaine inclusion decreased MDA content and increased CAT activity,GSH content and GSH/GSSG ratio in liver(P<0.05)and activities of SOD and GPX in both liver and hepatic mitochondria(P<0.05)compared with HS.The HS led to less mRNA expression of GPX and avian uncoupling protein(avUCP)in liver,whereas betaine increased mRNA expression of GPX and avUCP in liver under HS.The mRNA expression of SOD and CAT in liver were no different among groups.It can be concluded as follows:(1)Dietary betaine supplementation did not affect growth performance of broilers,but was effective in reducing abdominal fat deposition in a dose-dependent manner.The lower abdominal fat deposition was related to reducing hepatic FAS and increasing PPARa,CPT-I and HADH mRNA expression in liver.(2)Dietary supplementation with 750 mg/kg betaine was effective in improving breast muscle percentage and the crude protein content in breast muscle of broiler.Moreover,dietary supplementation with 750 mg/kg betaine had positive effect on water holding capacity and antioxidant function in breast muscle of broilers.(3)Dietary betaine supplementation relieved the negative effects of HS on growth performance and redox state of broilers,which was reflected as increased ADG,ADFI and antioxidant function in both liver and hepatic mitochondria.