Energy Requirement And Metabolomics For Growing Pigs During Maintenance Status

Four experiments were conducted to determine the energy requirement for maintenance of growing pigs and investigate the metabolic mechanism of maintenance in growing pigs using the techniques of indirect calorimetry and metabolomics.In Exp.1,the effect of fasting time on energy metabolism and plasma metabolites in growing pigs was determined.Nine barrows(45.2 ± 1.7 kg BW)were allotted to 1 of 3 treatments by repeated measures design.The experiment included 7 d of adaptation period and 7 d of experimental period.Pigs were transferred to respiratory chambers and fed a corn-soybean meal diet at 2,400 kJ ME/kg BW0.6 ·d-1 to determine heat production(HP)and respiratory quotient(RQ)of fed state during d 1 to 5 of experimental period.The last 2 days of experimental period were divided into 24 h fasting and 48 h fasting treatment,respectively.Plasma samples of each pig were collected from the anterior vena cava at the end of each treatment for metabolomics testing.HP and RQ were no significant difference between 24 h fasting and 48 h fasting,which were lower than those of fed state(P<0.01).The nitrogen concentration of urine tended to decrease with fasting(P<0.10).Metabolomics analysis between the fed and fasted state revealed differences in 15 compounds,most of which were not significantly different between 24 h fasting and 48 h fasting.Identified compounds were enriched in metabolic pathways related to linoleic acid metabolism,amino acid metabolism,sphingolipid metabolism,and pantothenate and CoA biosynthesis.Exp.2 was conducted to determine the energy requirement for maintenance of growing pigs based on regression analysis technique.Thirty-six growing pigs(26.3±1.7 kg)were allotted to 1 of 6 treatments with 6 replicates per treatment in a randomized complete block design.Treatments were included 6 feeding level which were calculated as 50%,60%,70%,80%,90%or 100%of the estimated ad libitum metabolizable energy intake(MEI).All pigs were individually housed in metabolic crates for thirty days and weighed every five days.Moreover,each pig from each treatment was placed in the open-circuit respiration chambers to measure HP and energy retained as protein(REP)and fat(REf)every five days.The average daily gain(ADG)and HP,as well as the REp and REf,linearly increased with increasing feed intake(P<0.01).β-hydroxybutyrate(BHBA)concentration of serum tended to increase with increasing feed intake(P = 0.08).The regression equations of MEI on ADG were MEI(kJ/kg BW0 6·d-1)1.88 × ADG(g/d)+ 782(R2 = 0.86,P<0.01)and ME requirement for maintenance(MEm)was estimated at 782 kJ/kg BW0.6·d-1.Furthermore,growing pigs will deposit protein and oxidize fat if provided feed at the estimated maintenance level.In Exp.3,the effect of metabolizable energy feeding level for maintenance on plasma metabolites in growing pigs was determined by repeated measures design.Ten barrows(22.5 ± 0.5 kg BW)were kept in metabolism crates and cathetered in the precaval vein during adaptaion period.Pigs were fed a corn-soybean meal diet at 782 kJ ME/kg BW0.6·d-1 during d 1 to 8 of the experimental period and then were re-feeding at 2,400 kJ ME/kg BW0.6·d-1 on d 9.Plasma samples of each pig were collected by catheter on the morning of d 1,3,5,7,9,and 10 respected respectively as the plasma samples of the day before and were used for metabolomics testing.Results showed that the concentration of plasma urea nitrogen decreased under metabolizable energy feeding level for maintenance(P<0.01).Eleven identified compounds were up-regulated and six ones were down-regulated under metabolizable energy feeding level for maintenance.Furthermore,all of them were not significantly different during d 4 to 8 of metabolizable energy feeding level for maintenance.In Exp.4,plasma metabolomics was conducted to identify biomarkers of maintenance metabolism in growing pigs by repeated measures design.Six barrows(28.6 ± 0.5 kg BW)were kept in metabolism crates for an experimental period of 21 d.After a 7-d adaptation period,all pigs were fed at 2,400 kJ ME/kg BW0.6 d-1 during d 1 to 7 and fed at 782 kJ ME/kg BW0.6·d-1 during d 8 to 14 of experimental period.Plasma samples of each pig were collected from the anterior vena cava on the morning of d 8 and 15 for metabolomics testing.Results showed that metabolomics analysis between the fed and maintained state revealed differences in 16 compounds.Identified compounds were enriched in metabolic pathways related to linoleic acid metabolism,tryptophan metabolism,and alanine,aspartate and glutamate metabolism.The linoleic acid,glutamine and tyrosine may be the potential biomarkers of maintenance status in growing pigs.In conclusion,ME requirement for maintenance was estimated at 782 kJ/kg BW0.6·d-1 based on regressing ADG on MEI in growing pigs.The decrease in HP and RQ of growing pigs under maintenance metabolism condition were associated with the alterations of linoleic acid metabolism,glucogenic amino acid metabolism and ketogenic amino acid metabolism.The linoleic acid,glutamine and tyrosine may be the potential biomarkers of maintain energy metabolism in growing pigs.