| Low-protein diets formulated with industrially synthesized crystalline amino acids can greatly reduce feed costs and alleviate the shortage of protein raw materials.The application of protease preparation can improve the digestion and absorption of feed nutrients,indirectly reduce the content of dietary crude protein and reduce nitrogen emission.Through the above measures,the implementation of low-protein diet technology can not only reduce the import dependence of soybean meal raw materials,but also save costs,improve environmental pollution,and make full use of domestic miscellaneous meal,corn and various amino acid products.This experiment was conducted to investigate the effects of amino acid or protease supplementation on performance,nutrient digestibility,key liver growth genes,intestinal amino acid transporter genes and TOR pathway related genes in broilers by reducing dietary crude protein level by two percentage points.A total of 540 1-day-old AA white-feathered broilers with similar body weight were selected and randomly divided into 5 groups with 6 replicates in each group and 18 chickens in each replication,half male and half female.Bords in the control group(NC)was fed with basic diet(23%CP in the early period,20%CP in the late period);the low protein group(LP)was fed with low protein diet(21%CP in the early period,18%CP in the late period);amino acid balance group(LP+AA)was fed with low protein diet(21%CP in the early period,18%CP in the late period)and added L-lysine hydrochloride.DL-methionine and L-threonine reached the feeding standard of AA broilers,protease group(LP+PRO)was fed with low protein diet(21%CP in the early period,18%CP in the late period)and added with 500 mg/kg protease(the enzyme activity is 30 000 U/g),amino acid balanced protease group(LP+AA+PRO)was fed with low protein diet(21%CP in the early period,18%CP in the late period)and added with L-lysine hydrochloride,DL-methionine,L-threonine and 500 mg/kg protease.The experimental period was 42 days.The results showed that:(1)The average body weight(BW)of 21 d and 42 d and the average daily gain(ADG)and average daily feed intake(ADFI)of 1～21 d,22～42 d and 1～42 d of the LP group were significantly lower than NC group(P<0.05);the BW of 21 d and 42 d and the ADG and ADFI of 1～21 d,22～42 d and 1～42 d of the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than LP group(P<0.05),and the BW of 42 d of the three groups was not significantly different from that of the control group(P>0.05),but the BW of 21 d and 42 d and the ADG and ADFI of 1～21 d and 1～42 d of the LP+AA+PRO group were significantly higher than those of LP+AA and LP+PRO groups(P<0.05).The breast muscle rate and leg muscle rate in the LP group were significantly lower than those in the NC group(P<0.05);the breast muscle rate and leg muscle rate in the LP+AA group,LP+PRO group,and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05)),and the breast muscle rate and leg muscle rate in the LP+AA+PRO group were significantly higher than those in the LP+AA group and LP+PRO group(P<0.05);the abdominal fat rate in the LP+AA group was significantly higher than that in the NC group,LP group,and LP group+PRO group and LP+AA+PRO group(P<0.05).The contents of serum total protein(TP),albumin(ALB),and uric acid(UA)in the LP group was significantly lower than those in the NC group(P<0.05),and the content of serum total cholesterol(CHO)was significantly higher than that in the NC group(P<0.05);the contents of serum TB and ALB in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05);the content of serum UA in the LP+AA group,LP+PRO group and LP+AA+PRO group was significantly lower than that in the NC group(P<0.05),and the content of serum urea nitrogen(BUN)in the LP+AA+PRO group was significantly lower than that of the NC group(P<0.05),the content of serum CHO in the LP+AA group was significantly higher than that in the NC group,LP+PRO group and LP+AA+PRO group(P<0.05).(2)The digestibility of crude fat in the LP group was significantly lower than that in the NC group(P<0.05);the digestibility of crude protein,crude fat,calcium and phosphorus in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05),the digestibility of crude protein and phosphorus in the LP+AA+PRO group were significantly higher than those in the LP+AA and LP+PRO groups(P<0.05).The digestibility of tyrosine,methionine,leucine and phenylalanine in the LP group were significantly lower than those in the NC group(P<0.05);the digestibility of threonine,tyrosine,valine,methionine,leucine,phenylalanine and lysine in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05);the digestibility of threonine and methionine in the LP+AA+PRO group were significantly higher than those in the LP+AA group and LP+PRO group(P<0.05).The pancreatic trypsin,lipase,amylase and the duodenal trypsin and amylase activities in the LP group were significantly lower than those in the NC group(P<0.05);the pancreatic trypsin,lipase,amylase and the duodenal trypsin and amylase activities in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05),and the LP+AA+PRO group pancreatic trypsin and duodenal trypsin And amylase activity were significantly higher than those in LP+AA group and LP+PRO group(P<0.05).(3)The expression levels of IGF-I,IGF-IR,GH and GHR genes in the liver of the LP group were significantly lower than those in the NC group(P<0.05),and the expression level of IGFBP-I gene was significantly higher than that in the NC group(P<0.05),the expression level of IGFBP-I gene in LP+AA+PRO group was significantly lower than that in NC group(P<0.05);the expression levels of IGF-I,IGF-IR,GH and GHR genes in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05),and the expression level of IGFBP-I gene was significantly lower than that in the LP group(P<0.05);the expression levels of IGF-I,GH and GHR genes in the LP+AA+PRO group were significantly higher than those in the LP+AA group and LP+PRO(P<0.05),and the expression level of IGFBP-I gene was significantly lower than that in the LP+AA group and LP+PRO(P<0.05).The expression levels of duodenum SLC7A1,SLC7A5,SLC7A7,jejunum SLC7A1,SLC7A7 and ileum SLC1A4,SLC7A1,SLC7A5,SLC7A7 genes of the LP group were significantly lower than those in the NC group(P<0.05).The expression levels of duodenal SLC7A1,SLC7A5,jejunum SLC7A1,SLC7A7 and ileum SLC7A1,SLC7A5,SLC7A7 genes of the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05).The expression levels of the duodenal SLC7A7 gene and the ileum SLC7A5 and SLC7A7 genes in the LP+AA+PRO group were significantly higher than those in the LP+AA group and LP+PRO group(P<0.05).The expression levels of TOR,S6K1 and 4E-BP1 genes in the breast and leg muscles of the LP group were significantly lower than those of the NC group(P<0.05),the expression levels of TOR,S6K1 and 4E-BP1 genes in the LP+AA group,LP+PRO group and LP+AA+PRO group were significantly higher than those in the LP group(P<0.05);the expression levels of TOR gene in breast muscle and S6K1 and 4E-BP1 genes in leg muscles of the LP+AA+PRO were significantly higher than those in LP+AA and LP+PRO groups(P<0.05).In summary,reducing the level of dietary crude protein by two percentage points seriously damages the health of broilers.Supplementation of amino acids or protease can improve the expression of key liver growth genes and intestinal amino acid carrier genes at the molecular level,and activate the skeletal muscle TOR signaling pathway,enhance the activity of digestive enzymes,improve the digestibility of nutrients,promote the deposition of proteins,and improve growth performance,the effect of supplementing amino acid and protease at the same time was more significant. |
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