Effect Of HMB On Muscle Protein Degradation In Immune-Stressed Piglets And Its Mechanism

Weaning piglets have immature physiological function and poor stress resistance.It is inevitable to contact various antigens in the process of weaning and transferation.Therefore,weaning piglets are vulnerable to immune stress,resulting in decreased feed intake of piglets,increased protein degradation of muscle tissue,negative nitrogen balance,and poorer growth performance.Immune stress also impairs the growth performance of the finishing stage,which causes a great economic loss to pig production.The purpose of this study is to investigate the effects of dietary supplementation with Hydroxy-Hydroxy-beta-methylbutyrate(HMB)on lipopolysaccharide(LPS)induced-muscle protein degradation in piglets and to explore the underlying mechanisms.60 healthy male piglets(21 ± 2 days old,5.86 ± 0.18 kg)were randomly divided into the following six groups(n = 10)according to the principle of similar weight:(1)control group(Group A,fed with basal diet);(2)0.60% HMB group(Group B,fed with basal diet with 0.60% HMB-Ca supplementation);(3)1.20%HMB group(Group C,fed with basal diet with 1.20% HMB-Ca supplementation);(4)LPS group(Group D,fed with basal diet,LPS injection);(5)LPS + 0.60% HMB group(Group E,fed with basal diet with 0.60% HMB-Ca supplementation,LPS injection)to the basic diet;(6)LPS + 1.20% HMB group(Group F,fed with basal diet with 1.20%HMB-Ca supplementation,inject LPS).The experiment lasted for 15 days.The LPS group was injected intraperitoneally with LPS every other day from the first day of the feeding experiment.The initial injection was 80 μg/kg BW,and the subsequent injection dose was increased by 30% each time.The same dose of saline was injected to the control group and HMB group at the same time.After the feeding program,piglets were sacrificed and sampled to measure the growth performance,blood parameters,muscle protein degradation rate and m RNA and protein expression levels of related factors.The results showed: 1)compared with the control group,the ADG and ADFI of LPS piglets were significantly reduced,while the feed/gain ratio was significantly increased(P < 0.05).Supplementing 0.60%HMB to the diet could increase the ADG and ADFI of LPS piglets,reduce the feed/gain ratio(P < 0.05),and improve the lean ratio to the level of the control group;2)compared with the control group,the concentrations of BUN and inflammatory cytokines(IL-1β and TNF-α)in LPS piglets are significantly increased(P < 0.05),while 0.60% HMB supplementation reduced the concentrations of BUN,IL-1β and TNF-α in LPS piglets(P < 0.05);3)compared with control group,LPS injection can significantly increase serum concentration of 3-Me His and protein degradation ratio in longissimus dorsi muscle(P < 0.05).There was no significant effect on protein degradation ratio in soleus muscle(P > 0.05),while 0.60%HMB supplementation can reduce serum concentration of 3-Me His and protein degradation ratio in longissimus dorsi muscle of LPS piglets,and significantly alleviate cell apoptosis in longissimus dorsi muscle and soleus muscle(P < 0.05);4)compared with the control group,the phosphorylation level of Akt and Fox O3 a in longissimus dorsi muscle of LPS piglets was significantly reduced(P < 0.05),while dietary supplementation with 0.60% HMB restored the phosphorylation level of Akt and Fox O3 a to the control level,and significantly reduce the protein expression levels of Mu RF1 and MAFbx(P < 0.05);5)compared with the control group,LPS significantly down-regulated the m RNA expression of mitochondrial biosynthesis-related genes(such as AMPKα,Sirt1,and PGC-1α)in longissimus dorsi muscle of piglets,while reducing citrate synthase activity(P < 0.05).However,dietary supplementation with0.60% HMB can up-regulate the expression of AMPKα,Sirt1 and PGC-1α in the longissimus dorsi muscle of LPS piglets and increase the activity of citrate synthase(P<0.05).In conclusion,HMB can alleviate LPS-induced muscle protein degradation in weaning piglets through regulating the Akt-Fox O3 a pathway to inhibit ubiquitinated protein degradation pathways and improving mitochondrial function.The suitable dosage of HMB in piglet diets was 0.60%.This study provides nutritional control methods for improving the growth performance of immune-stressed piglets and lays a theoretical foundation for the development and utilization of HMB.