Effects Of Different Nutrition Levels Dietary On Growth Performance,Carcass Traits And Meat Quality Of Ningxiang Pigs

Ningxiang pig is a high-quality local pig breed in China with a delicious taste,whereas is limited to promote because of its low lean meat rate and high fat rate.The interaction of dietary energy,protein,and lysine on pig carcass traits have been reported,but at present,there are few studies on the optimization of fat deposition in Ningxiang pigs by the combination of these three nutrients Therefore,this study used the Central Composite Design to investigate the effect on the carcass composition of dietary energy,protein,and lysine in Ningxiang pigs,and the mechanism of the effects of energy excess/restriction and protein excess/restriction on the growth and carcass quality in Ningxiang pigs was further studied.320 Ningxiang pigs（about 43kg）were selected and randomly divided into 20 groups with 4 replicates in each group and 4 pigs in each replicate.The nutritional and physiological effects of dietary energy,protein and lysine on Ningxiang pigs were studied from the aspects of growth performance,carcass traits,meat quality,liver lipid metabolism and intestinal health.The main results are as follows:1)Effects of dietary energy,protein and lysine levels on growth performance,carcass quality and meat quality of Ningxiang pigsIn terms of the highest feed efficiency,the suitable dietary protein/energy to Ningxiang pigs in the fattening period is about 9.22 g/MJ,with nutrients combination of DE 15.22MJ/kg,CP 14.03%,and Lys 0.7%.As far as the optimal carcass composition and intramuscular fat deposition are considered,which refer the lowest back fat thickness and percentage of perirenal fat and carcass fat,as well as the maximized lean meat percentage and IMF,the nutritional level combination was showed as DE 11.88 MJ/kg,CP 9.99%,Lys0.70%,which obtained F/G 4.72,backfat thickness 34.81 mm,perirenal fat 3.46%,fat percentage 36.01%,lean meat percentage 40.56%,and IMF content 4.20%.Among the three factors,lysine has the greatest impact on back fat thickness and perirenal fat,energy has the greatest impact on intramuscular fat and carcass fat.There is an interaction between energy and protein on back fat thickness and fat percentage.Energy and lysine also interacted on back fat thickness2)Study on the mechanism of excessive and restrictive energy on growth,carcass quality and meat quality of fattening Ningxiang pigsExcessive energy increased ADG and fat percentage（P <0.05）.F/G decreased with increasing energy level（P <0.05）.Excessive energy increased the apparent digestibility of crude protein and total energy（P <0.01）,as well as jejunal neutral protease（NP）and ileal lipase（LPS）activities（P <0.05）;as energy levels increased,the apparent digestibility of crude ash,dry matter and crude fat was increased（P <0.01）.Restrictive energy reduced serum GH and IGF-1 concentrations（P <0.05）.Excessive energy increased the shear force,IMF,TG content and muscle fiber CSA of the longissimus dorsi（P <0.05）,and up-regulated the m RNA expression of My HC IIb,FABP4 and FAS of the longissimus dorsi（P <0.05）.Regarding liver lipid metabolism,restrictive energy increased the content of HDL-C,decreased the content of TG,NEFA and TC,and increased the expression of LPL m RNA in the liver（P <0.05）.Excessive energy increased the relative weight of the liver,increased the content of LDL-C and TBA,and up-regulated the m RNA expression of ACC,FAS and SREBP-1C in the liver（P <0.05）.Excessive or restricted energy reduced the content of isobutyric acid,isovaleric acid,and valeric acid in the colon（P <0.05）.Restrictive energy also reduced the content of propionic acid and butyric acid（P <0.05）and has a trend to decreased acetic acid（P =0.081）and total SCFA content（P =0.066）.Excessive or restrictive energy reduced the abundance of Bacteroides and Tenericutes and increased the abundance of Firmicutes.Restrictive energy increased the ratio of Firmicutes and Bacteroides（P <0.05）.In the dominant bacteria at the genus level,excessive energy reduced the abundance of Terrisporobacter,increases the abundance of Clostridium_sensu_stricto₁,and several members of Lacetospiraceae that are positively correlated with fat digestibility.Restrictive energy increased the abundance of Streptococcus and decreased the abundance of Ruminococcaceae_UCG-005 and Ruminococcaceae_NK4A214_group that were positively correlated with the content of acetic acid,propionic acid,butyric acid,and total SCFA.Serum metabolomics results showed,there were nine common serum differential metabolites of glycerophospholipids between EE group and RE group.Seven of them belong to phosphatidylcholine（PC）,which mostly were up-regulated in EE group but down-regulated in RE group when compared with CON group.PC（18:0/22:5（4Z,7Z,10 Z,13Z,16Z））（KEGG ID: C00157）was found to be significantly down-regulated in Groups EE vs CON and Groups RE vs CON,while PC（20:3（5Z,8Z,11Z）/16:0（KEGG ID: C00157）were up-regulated in Groups EE vs CON and down-regulated in Groups RE vs CON,respectively.These phosphatidylcholines hit the pathway of glycerophospholipid metabolism.Excessive energy also lowered the relative content of trimethylamine oxide（TMAO）.The above results indicate that excessive energy can increase the digestibility to fat and other nutrients and the activities of related digestive enzymes,thereby promoting the growth of Ningxiang pigs and increasing carcass fat content.Excessive energy up-regulated the expression of adipogenic genes to promote fat deposition in muscles,whereas also increased the differentiation and growth of glycolytic muscle fibers,significant decreasing meat tenderness,which has greater negative impact to meat quality.Excessive energy promoted cholesterol and bile acid metabolism,while up-regulated the expression of adipogenic genes,causing fat deposition in liver.Dietary energy changes may affect liver lipid metabolism by regulating the glycerophospholipids metabolism pathway.PC（20:3（5Z,8Z,11Z）/16:0）（KEGG ID: C00157）and other PCs may be potential biomarkers.Excessive energy may also participate in the metabolism of glycerophospholipids by regulating the intestinal bacteria.3）Study on the mechanism of excessive and restrictive protein on growth,carcass quality and meat quality of fattening Ningxiang pigsThere was no significant difference in growth performance.Excessive protein reduced fat percentage（P <0.05）,and other carcass traits were not significantly changed.Excessive protein increased the apparent digestibility of protein and crude fat,as well as jejunal LPS activity and ileal NP activity（P <0.05）;excessive or restrictive protein increased the digestibility of dry matter,ash,and energy（P <0.05）.Excessive or restrictive protein increased the brightness（L*）,redness（a*）,yellowness（b*）and IMF content of the longissimus dorsi at 24 h after slaughter and up-regulated the expression of ACC,PPARγ,and FABP4 m RNA（P <0.05）.Compared with restrictive protein,excessive protein reduced the crude protein and non-essential amino acid（NEAA）content in the longissimus dorsi,and the total amino acid content decreased with the increase of dietary protein level（P <0.05）.In addition,excessive protein up-regulated expression of CAPN1 m RNA,while restrictive protein up-regulated expression of CAST m RNA（P <0.05）,which may explain the changes in the degree of protein degradation in muscle caused by changes in dietary protein levels.In serum,excessive protein increased TG,BUN,GLB and IL-6 content（P <0.05）.TP content was also increased,ALB/GLB was decreased（P <0.05）,ALT and AST content trend to be increased（P =0.063,P =0.055）compared with restrictive protein group.In the ileal mucosa,restrictive protein reduced IL-8 and TNF-α content,excessive protein increased the IL-1content,and the IL-6 content increased with the increase in protein level（P <0.05）.In addition,excessive protein increased the relative weight of liver and kidney（P <0.05）.The above results showed that excessive protein reduced the protein utilization rate,increased the burden of liver metabolizing protein,and even caused liver damage and intestinal inflammation.Restrictive protein reduced the content of acetic acid,propionic acid,butyric acid,and total SCFA in the colon contents（P <0.05）.Excessive or restrictive protein reduced the Shannon index of microorganisms in the colon and the abundance of Bacteroides and Tenericutes,increased the abundance of Firmicutes,and reduced the abundance of[Eubacterium]_coprostanoligenes_group,Ruminococcaceae_NK4A214_group,Ruminoco ccaceae_UCG-002（P <0.05）.Excessive protein increased the abundance of Romboutsia and Turicibacter that were positively correlated with nutrient digestibility,increased the abundance of Clostridium_sensu_stricto₁,a potential pathogenic bacteria positively correlated with serum GLB and ALT content（P <0.05）,promoted hindgut protein fermentation and the proliferation of harmful bacteria.To sum up,excessive energy increased carcass fat content,while also caused fat deposition in muscles and liver: the former improves meat quality to a limited extent,while the latter damages liver health.Affecting liver lipid metabolism（mainly bile acid metabolism）possibly by regulating the glycerophospholipid metabolism pathway as well as participating in glycerophospholipid metabolism by regulating the intestinal bacteria.Excessive protein reduced carcass fat content,but increased protein degradation in muscles,increased IMF deposition,reduced protein utilization,aggravated the metabolic burden to liver and kidneys,and promoted the proliferation of harmful intestinal bacteria,may arousing inflammation in the body and threatening the health of the liver and intestines.In comparison,restrictive energy or protein is more beneficial to liver and intestinal health and can maintain growth performance,carcass quality,and meat quality,thus,it has certain applicability to fattening Ningxiang pigs.It further proves the acceptability to lower dietary energy and protein levels and the possibility that reduce the carcass fat content without affecting of IMF deposition in Ningxiang pigs.