Study On The Effects Of Balancing Low-protein Diets With Glutamate On The Utilization Of Protein And Growth Performance Of Finishing Pigs

Low-protein diet is an important measure that is currently being used to reduce nitrogen pollution in the pig farming industry.However,traditional low-protein diets,which contain only balanced essential amino acids,also reduce pig growth performance.In this study,we added glutamic acid to the balanced low-protein diet,which contains only four essential amino acids(lysine,methionine,threonine,and tryptophan),and investigated its effect on the protein utilization and growth performance of fattening pigs.Experiment 1: metabolism test.Six healthy Duroc×Landrace×Large White three-way cross hybrid barrows weighing 54.2±2.2 kg were randomly allocated into three groups using the 3×3 Latin square design.The diets of the three experimental groups were: 14% crude protein(CP)(control),12.5% CP + glutamic acid,and 11% CP + glutamic acid.Feces and urine were collected to measure nitrogen and energy metabolisms.The results showed that adding glutamic acid to the low-protein diet significantly decreased the nitrogen intake,fecal nitrogen,urine nitrogen,and total nitrogen emission(P<0.05)in fattening pigs,and significantly increased the ratio of nitrogen deposition to nitrogen intake(P<0.05).Experiment 2: growth performance test.Thirty healthy Duroc×Landrace×Large White three-way cross hybrid barrows weighing 57.4±0.2 kg were randomly allocated into 3 groups,with 10 replicates each and 1 pig per replicate.The pigs were reared in individual cages.The test diet was the same as that used in the metabolism test.The experimental period was 35 d,and the initial weight,final weight,and feed intake of test pigs were recorded.At the end of the experiment,anterior vena cava blood samples were collected from 5 pigs in each group,and the pigs were slaughtered,following which the intestinal mucosa,liver,chyme,and other samples were collected from the slaughtered pigs to measure indexes of metabolisms and gut microflora.The results showed that adding glutamic acid to the low-protein diet did not significantly affect the daily weight gain of the fattening pigs(P>0.05).However,after the addition of glutamic acid,serum urea nitrogen and free fatty acid levels(P<0.05)decreased as the protein levels in their diets decreased.The oxaloacetic acid,α-ketoglutaric acid,and pyruvic acid levels in the jejunum mucosa of animals in the low-protein+Glu groups were significantly higher than in those of animals in the control group(P>0.05).The enzyme activity of glutamic oxaloacetic transaminase,glutamic-pyruvic transaminase,glutaminase,and glutamine synthetase were also significantly higher in animals in the low protein+Glu groups than in those in the control group(P>0.05).Small intestinal villi in animals in the 12.5% CP+Glu group was significantly higher than in those in the control group and in the 11% CP+Glu group(P<0.05);the crypt depth was not significantly different among all groups(P>0.05).Compared with the control group,the abundance of the Verrucomicrobia phylum and Bacteroidia class were significantly higher in the cecum of the low protein+Glu groups.However,the abundance of pathogenic gut microflora,such as the Spirochaetae and β-Proteobacteria classes,were reduced.Adding glutamic acid to the low-protein diet mainly affected the glycerophosphoric acid,the arginine and proline,and the alanine,aspartic acid,and glutamic acid metabolic pathways in the jejunum mucosa.Our study results show that adding glutamic acid to the balanced low-protein diet can decrease the CP level in the basal diet by 3%,significantly reducing nitrogen emission and significantly increasing protein utilization efficiency,but had no significant negative effects on the growth performance of fattening pigs.Our results demonstrate the importance of adding non-essential amino acids,such as glutamic acid,to low-protein diets.