Effects Of Diets With Different Fat And Bile Acids Levels On Growth Performance,Meat Quality And Lipid Metabolism In Broilers

With the rapid development of modern livestock industry,people normally cannot pay sufficient attention to health and the meat quality of broilers,when they pursue the rapid growth of broilers.Lipids provide livestock and poultry with energy and necessary nutrients for their growth and are one of the most important raw materials in the feed.However,broilers cannot fully digest and absorb the lipids in the feed due to the limited digestive enzymes and emulsifiers in the intestine.As one of the most commonly used feed additives,emulsifiers can enhance the emulsification of fats and fat-soluable nutrients in animal digestive tract,thereby enhancing the nutrient absorption and promoting the growth performance of animals.At present,bile acids(BAs)are used as a natural emulsifier in animal husbandry.It can not only promote the digestion and utilization of lipids in animals,but can also be used in human medicine as a signal molecule,which has positive therapeutic effects on fatty liver in humans.In this study,Arbor Acres(AA)broilers were used as an animal model.The effects of BAs the on growth performance,meat quality,blood lipid levels and liver lipid metabolism of broilers were investigated by adding BAs to diets with different fat levels.This study may provide scientific basis and reference to the livestock industry and animal husbandry medicine industry.The study is divided into three parts as follow:Experiment 1 was conducted to investigate the effects of diets with different fat and bile acids levels on growth performance and nutrient utilization rate in broilers.The experiment period was 42 d and was divided into starter period(1-21 d)and finisher period(22-42 d).480 one-day-old AA broilers(45.01±0.26 g)were allotted to a 2×2 factorial design with 2 levels of dietary fat(basic diets:2%in the starter period,4%in the finisher stage;high-fat diets:3%in the starter period and 5.5%in the finisher period)and 2 levels of BAs(level 1:starter 0,finisher 0;level 2:starter 60 g/t,finisher 80 g/t).Therefore,there are 4 groups:BF(basic diets),BF-B(basic diets+BAs),HF(high-fat diets),and HF-B(high-fat diets+BAs),with 8 replicates of 15 broilers each group.The body weight and feed intake were recorded to calculate the growth performance.The fecal sample and intestinal chyme were collected to determine the feed nutrient utilization rate and digestive enzymes activity,and the heart,spleen and thymus were weighed for organ indexes.The results showed that:(1)1-21 d,compared with the basal diets,high-fat diets significantly reduced the feed/gain ratio(F/G)of broilers(P<0.05),while BAs diets significantly increased broilers’21 d body weight and average daily gain(P<0.05);21-42 d,compared with non-BAs diets,BAs diets significantly reduced broilers’ F/G(P<0.05);1-42 d,dietary supplementation with BAs significantly reduced the full-term F/G(P<0.05).(2)On 21 d,dietary fat and BAs levels had no significant effect on organ indexes in broilers(P>0.05).On 42 d,dietary supplementation of BAs decreased thymus index(P<0.05).(3)On 21 d and 42 d,dietary supplementation of BAs significantly increased the crude fat digestibility of broilers(P<0.05),while high-fat diets had no significant effect on the feed nutrient utilization rate of broilers in the starter and finisher stages(P>0.05).(4)On 21 d,dietary supplementation of BAs significantly increased ileal lipase activity in broilers compared with the broilers fed without BAs diets(P<0.05);On 42 d,dietary supplementation of BAs significantly increased jejunum lipase activity in broilers(P<0.05).Experiment 2 was conducted to investigate the effects of diets with different fat and bile acids levels on meat quality and abdominal fat deposition in broilers.The experiment design was the same as that of experiment 1.The results showed that:(1)Compared with the basal-fat diets groups,the high-fat diets groups had significantly increased abdominal fat percentage(P<0.05),while the addition of BAs to the diets significantly reduced the abdominal fat percentage(P<0.05);dietary supplementation with BAs significantly increased broilers’ breast muscle rate and thigh muscle rate(P<0.05)compared with non-BAs diets.(2)Compared with broilers in the basal-fat diets groups,the area and perimeter of fat cells in the abdominal fat in high-fat diets groups were significantly larger and these cells were arranged more closely(P<0.05),while these two parameters were significantly reduced upon the addition of BAs in diets(P<0.05).(3)Compared with the diets without BAs,the diets with BAs significantly reduced the pH24h value and increased the yellow value in the breast muscles of broilers(P<0.05).Compared with the diets without BAs,the addition of BAs in diets significantly reduced the pH45min and pH24h values of thigh muscles of broilers(P<0.05).In addition,BAs also significantly reduced the drip loss of 48 h of thigh muscles(P<0.05).(4)Compared with the broilers fed without BAs,the intramuscular fat content in the breast and thigh muscles were significantly increased in broilers fed with BAs diets(P<0.05).Experiment 3 was conducted to investigate the effects of diets with different fat and bile acids levels on serum lipid levels and liver lipid metabolism in broilers.The experiment design was the same as that of experiment 1.The results showed that:(1)On 21 d,the liver index and liver total triglyceride(TG)levels of the broilers fed with B As were significantly lower than those of the broilers fed without BAs(P<0.05);On 42 d,compared with the basal diets groups,liver index and TG levels in high-fat diets groups were significantly increased(P<0.05),while dietary supplementation of BAs significantly decreased liver index and liver TG content(P<0.05).And compared with adding BAs in basal diets,adding BAs to high-fat diets reduced the liver index of broilers more significantly(P<0.05).(2)On 21 d and 42 d,the serum alanine aminotransferase(ALT)and aspartate aminotransferase(AST)activity in the high-fat diets groups were significantly higher than those in the basal diets groups(P<0.05).Dietary supplementation of BAs significantly reduced serum ALT and AST activity in broilers on 42 d(P<0.05).(3)Compared with the basal diets,the high-fat diets significantly increased the serum TG content on 21 d and 42 d and increased serum high-density lipoprotein cholesterol(HDL-C)content on 42 d in broilers(P<0.05).The diets supplemented with BAs significantly reduced serum TG levels on 21 d and 42 d and reduced serum low-density lipoprotein cholesterol(LDL-C)levels on 42 d(P<0.05);(4)On 21 d and 42 d,the activity of lipoprotein lipase(LPL)in the liver of broilers fed with high-fat diets were significantly higher than that of broilers fed with basal diets(P<0.05).The addition of BAs in diets significantly decreased the LPL activity of liver in broilers on 42 d(P<0.05).(5)The mRNA expression levels of sterol regulatory elements in combination with transcription factor 1(SREBF1)of 21 d and 42 d,acetyl-CoA carboxylase(ACC)on 21 d and fatty acid synthase(FAS)on 42 d in the liver of broilers in high-fat diets groups were significantly increased(P<0.05),while the mRNA expression of carnitine palmitoyltransferase 1(CPT1)in the liver was significantly lower than that in the basal diets groups on 21 d and 42 d(P<0.05).Compared with non-BAs diets group,the mRNA expression levels of SREBF1 on 21 d and 42 d,ACC on 21 d and FAS on 42 d in BAs diets gruop were significantly decreased and the mRNA expression levels of peroxisome proliferator-activated receptor alpha(PPARα)and CPT1 were increased on 21 d and 42 d.In summary,high-fat diets could reduce the F/G of broilers in the starter stage.The high-fat diets could also increase lipid accumulation in the liver and cause abnormal serum lipid levels in broilers.Dietary supplementation of BAs could significantly increase the intestinal lipase activity and the utilization of dietary crude fat to promote the growth performance of broilers,and had positive effects on the meat quality of broilers.Dietary BAs could also upregulate the expression level of lipid hydrolysis-related genes and down-regulate the expression level of genes related to lipid synthesis.In addition,BAs could improve the serum lipid profile and reduce the body fat deposition by regulating lipid metabolism-related enzyme activities in broilers.