Immune Stress On Growth Performance And Protein Needs Of The Law

A 2x3 factorial nitrogen balance trial was conducted to explore the influence of immune stress and dietary crude protein(CP) on growth performance and protein utilization and requirement of young pigs. Immune system of pigs was activated in stress groups by intramuscular injection of Escherichia coli lipoploysaccaride(LPS, serotype O55:B5) . Pigs in non-stress groups were not challenged by LPS. Dietary protein levels were designed as 17%, 20%, and 23% . A total of 36 crossbred (Landracex Rongchang) pigs weaned at 28 days were randomly allotted to 6 treatments with 6 replicate each. The trial was conducted for 21 days. On d 1, d 3, d 5 and d 7 of the experiment, piglets in stress groups were challenged with LPS at a dose of 200ug/kg bogy weight. Pigs in non-stress groups were injected with 0.9% sterile saline. Feed consumption and bodyweight of pigs were recorded during the trial. CP digestibility, biological value and body protein retention were determined by nitrogen balance from d 3 to 21 d .Lymphocyte blastogenesis and serum immunoglobulins were measured to monitor piglets'immune status.The results showed: 1) Repeated injections of LPS increased significantly lymphocyte blastogenesis ratio on d 3 (PO.01), but lymphocyte blastogenesis ratio on d 14 was not significantly different among treatments, indicating immune system was activated by LPS injection. The level of serum immunoglobulins was not different between stress- and non-stress groups at each stage (P>0.05). 2) Immune challenge reduced growth performance of piglets. Average daily gain(ADG), average feed daily intake (ADFI) and feed efficiency (G/F) in stress groups were 43% ,25%, and 23% lower respectively than those in non-stress groups during d 1 to d 6 and ADG was 28% lower during d 1 to d 9. Growth performance during d 14 to d 21 was not affected by stress treatment (P>0.05). 3) Piglets consuming 17%CP diet had higher ADG and G/F than pigs fed 20% or 23%CP diet when piglets were challenged with LPS during d 1 to d 6. During d 14 to d 21, piglets fed 23%CP in stress group had the highest G/F ratio and ADG than pigs fed 17% or 20% CP diet. The results showed that piglets needed lower dietary crude protein(CP) during stress and higher CP after immune stress for their compensatory growth.. 4) LPS administration reduced the utilization efficiency of crude protein (P>0.05) and the effect was greater during d 3 to d 9 than that during d 14 to d 21. During d 3 to d 9, protein digestibility, biological value, protein retention were lower 3%,3%,15% respectively in stress groups compared with non-stress groups . Urinary nitrogen excretion in the stress groups increased by 43.8% compared to non-stress control during d 3 to d 6. 5) Dietary CP levels affected significantly protein retention in stress groups at each stage (P<0.00) with exception to the stage of d 3 to d 9.in conclusion, immune stress influences dietary protein utilization and pig performance. Dietary protein requirement during and after stress is inconsistent to that of healthy piglets. In this study, piglets need 17% CP during immune stress and 23%CP during the compensatory growth after stress, while healthy piglets need 20% CP during the same period.