Effects Of Dietary Lysine Levels On Meat Production Performance,Nutrient Digestibility And Metabolism Of Yacha Pigs

Lysine,as the first limiting amino acid for pigs,is the main amino acid which is involved in protein synthesis of body,has an important influence on the growth performance,carcass characteristics and meat quality of pigs.However,the research on the lysine requirement of the great flavor pigs with the local blood relation is still scarce.The purpose of this research is to study the effect of dietary lysine levels on the growth performance,carcass characteristics and meat quality of Yacha pigs by feeding experiment,digestion experiment and slaughter experiment,and to explore its possible mechanism through apparent nutrient digestibility and blood biochemical indexes.Complete random block design was used in the experiment.A total of 50 healthy Yacha pigs（half male and female,castrated）were divided into 5 groups according to the initial body weight.Each group was divided into 5 pens,and 2 pigs in each pen were randomly fed with one experiment diet.The experiment diet was formulated according to the Chinese feeding standard of local pigs.The experimental period was 18 weeks.According to body weight,the experiment was divided into three stages,each of which was designed with 5 different lysine levels.The dietary lysine levels in 15³0 kg were 0.63%（T1）,0.70%（T2）,0.75%（T3）,0.80%（T4）,0.85%（T5）,respectively.The dietary lysine levels in 30⁵0 kg were 0.47%（T1）,0.55%（T2）,0.63%（T3）,0.71%（T4）,0.79%（T5）,respectively.The dietary lysine levels in 50⁹0 kg were 0.36%（T1）,0.45%（T2）,0.54%（T3）,0.63%（T4）,0.72%（T5）,respectively.At the end of each stage,the pigs weighed on an empty stomach and collected blood and fecal samples to record weekly feed intake.The digestive test was carried out during the third stage of the experiment.Chromium trioxide was used as an external indicator for 7 days of pre-feeding and 3 days of formal fecal collection.At the end of the experiment,Yacha pigs,whose body weight was close to the average,were selected from the treatment groups with the lowest and highest average daily gain,respectively.These pigs were slaughtered and then their muscle,adipose tissue and bone samples were collected for analysis of the indexes.The main results are as follows:1.Changes in growth performance of Yacha pigs:With the increasing of dietary lysine levels,ADG and G/F were increased significantly（P<0.05,Linear）at 15³0 kg and30⁵0 kg,and the optimum growth performance was achieved in treatment 4.At 50⁹0 kg,there had no effect on the growth performance.2.Changes in apparent nutrient digestibility of Yacha pigs:With the increasing of dietary lysine levels,the digestibility of dry matter,gross energy,crude protein,total calcium and total phosphorus were increased significantly（P<0.05,Linear）at 50⁹0 kg.3.Changes in serum metabolites of Yacha pigs:With the increasing of dietary lysine levels,the blood glucose in serum increased significantly（P<0.05）at 15³0 kg,and the total protein tended to higher（0.05<P<0.10）at 30⁵0 kg.There had no effect on the GLU,TP,TC,TG,HDLC and LDLC at 50⁹0 kg.4.Changes in concentration of free amino acids in serum of Yacha pigs:With the increasing of dietary lysine levels,lysine（P=0.007,Linear increased）,threonine（P=0.049,Linear decreased）,glutamate（P=0.011,Quadratic）and proline（P=0.007,Linear increased）showed significant changes at 15³0 kg.Lysine（P<0.001,Linear increased）,cysteine（P=0.005,Linear decreased）,isoleucine（P=0.019,Linear decreased）,arginine（P<0.001,Linear increased）and proline（P=0.010,Linear decreased）showed significant changes at 30⁵0 kg.Methionine（P<0.001,Linear increased）,isoleucine（P<0.001,Linear increased）,leucine（P=0.019,Linear increased）,tyrosine（P<0.001,Linear increased）,phenylalanine（P=0.026,Quadratic）,arginine（P<0.001,Linear decreased）and proline（P=0.024,Linear increased）showed significant changes at 50⁹0 kg.The analyses correlation between the dietary lysine levels and the concentration of free amino acids in serum showed variable results.At 15³0 kg,30⁵0 kg and 50⁹0 kg,the concentration of lysine in serum was highly and positively correlated with the content of lysine in the diet.At 15³0 kg,the concentration of urea in serum was highly and positively correlated with the content of lysine in the diet,but showed highly and negatively correlation at 30⁵0 kg.At 15³0 kg and 50⁹0 kg,the concentration of threonine in serum was highly and negatively correlated with the content of lysine in the diet.At 15³0 kg,the concentration of valine and phenylalanine in serum was highly and negatively correlated with the content of lysine in the diet.At 50⁹0 kg,the concentration of cysteine,methionine,leucine,tyrosine and histidine in serum was highly and positively correlated with the content of lysine in the diet.At 30⁵0 kg,the concentration of isoleucine in serum was highly and negatively correlated with the content of lysine in the diet,but showed highly and positively correlation at 50⁹0 kg.At 30⁵0 kg,the concentration of arginine in serum was highly and positively correlated with the content of lysine in the diet,but showed highly and negatively correlation at 50⁹0 kg.At 15³0 kg and 50⁹0 kg,the concentration of proline in serum was highly and positively correlated with the content of lysine in the diet,but showed highly and negatively correlation at30⁵0 kg.5.Changes in carcass characteristics and meat traits of Yacha pigs:With the increasing of dietary lysine levels,the carcass weight,lean meat percentage and shear force of longissimus were increased significantly（P<0.05）,but the cooking loss of lumborum muscle was decreased significantly（P<0.05）.There had no effect on carcass length,dressing percentage,10^th-rib back fat thickness,loin area,pH,marbling score,meat color and drip loss of the longissimus.Further analysis to the contents of nutrient and the concentration of amino acids in the longissimus.We found that the content of moisture,crude protein and intramuscular fat in the longissimus were not affected with the increasing of dietary lysine levels.The contents of lysine,histidine and glycine in the longissimus increased significantly（P<0.05）with the increasing of dietary lysine levels.The content of aspartic acid,threonine,serine,alanine,valine,methionine,leucine and arginine tended to higher（0.05<P<0.10）with the increasing of dietary lysine levels.It was further proved that increased dietary lysine levels was helpful to increase the contents of amino acid in meat of Yacha pigs.The results showed that the daily lysine requirement of 15-30 kg,30⁵0 kg,50⁹0 kg Yacha pigs was 9.05 g/d,13.40 g/d,18.47 g/d respectively,and the optimal dietary lysine levels were 0.600,0.549,0.504 g/MJ ME,respectively.