Study On The Regulatory Effect Of Sodium Butyrate On Immune Response And Antioxidant Function In Broiler Chickens

Great economic losses brought about by immunological stress and oxidative injury in animal husbandry, as which leads to nutrition metabolism up-regulation, growth inhibition and poorer meat quality in poultry. And it has obtained widespread attention of scholars from various countries that adopting nutrition regulation method to alleviate the growth inhibition induced by immunological stress and oxidative injury, and eventually to promote the genetic potential growth of birds.Sodium butyrate, as a feed additive, has been confirmed positive effects on gastrointestinal development and growth performance in poultry. The mechanism however is still not clear till now. So, lipopolysaccharide (LPS) and corticosterone (CORT) were applied in this study for making immunological stress and oxidative injury model respectively to study the effects of free or fat-coated sodium butyrate on immune response, antioxidant function, nutrient metabolism, hormones changes and meat quality in broiler chickens, so as to investigate whether sodium butyrate could maintain normal growth performance and improve meat quality through regulating immune response and improve antioxidant function. In addition, the intestine development, intestinal mucosal immunity and apoptosis and related gene expression in broilers were studied to explore the mechanism of sodium butyrate on immune response and apoptosis, and to analyze whether sodium butyrate could maintain intestinal structure and function integrity through regulating intestinal mucosal immunity and apoptosis. Resolution of these issues will not only provide reference for further research, development and application of sodium butyrate in livestock and poultry industry, but also to provide a theoretical basis and scientific guidance for seeking green, effective additives to replace antibiotics, as well as to promote the establishment of domestic animals’health breeding models.1. The first part of the study was conducted to preliminarily investigate the effects of basal diets supplemented with different levels of sodium butyrate on growth performance, immune response and antioxidant function in broiler chickens. A total of 240 1-d-old male Arbor Acres broiler chicks (AA broiler chicks) were randomly allocated to 4 treatment groups and were fed with one of four diets, basal diets (control) or diets supplemented with sodium butyrate at level of 0.25,0.50,1.00 g/kg, respectively, for 42d. The results showed that there was no effect of dietary sodium butyrate on feed intake (FI), body weight gain (BWG) and feed to gain ratio (F/G) (P>0.05). Sodium butyrate supplementation(1.00 g/kg) significantly increased the thymus index at 21 day of age and antibody titers to Newcastle Disease Virus at 14 day of age (P<0.05), while greatly decreased the levels of serum IL-6, TNF-a and CORT in contrast to the control (P<0.05) at 21 day of age. On day 42, the level of serum IL-6 in broilers was markedly decreased by all the sodium butyrate diets in contrast to the control (P<0.01). Meanwhile, serum CORT level was significantly decreased by the 1.00 g/kg sodium butyrate diet. In addition, on day 21, compared with the control, dietary sodium butyrate supplementation at the level of 0.50 and 1.00 g/kg significantly elevated serum superoxide dismutase (SOD) (P<0.05) and catalase (CAT) (P <0.001) activities, while greatly decreased the level of serum MDA (P<0.05). On day 42, chickens fed 1.00 g/kg sodium butyrate diet had highest (P<0.001) CAT activity and lowest MDA (P<0.01) than the control. No significant difference was observed on the levels of serum IL-1βand Prostaglandin E2 (PGE2), activity of glutathione peroxidase (GSH-Px), and proliferation of peripheral blood lymphocyte (LTR) among treatments both at 21 and 42 day of age (P>0.05).2. Based on the results of the first part of the study, the present study was to investigate the effects of 1.00 g/kg dietary sodium butyrate and immunological stress mimiced by LPS injection (0.5mg/Kg-BW) on the immune response in broiler chicks. Meanwhile, in order to explore the mechanism of sodium butyrate on immune response, the intestine development and mRNA expression of pro-inflammatory cytokines and the level of activated NF-κB in intestinal mucosa were determined.2x2 factorial arrangement was used in this study. A total of 120 1-d-old AA broiler chickens were randomly allocated to 2 treatment groups and were fed on a control diet or 1.00 g sodium butyrate/kg diet. Each treatment had 6 replicates with 5 chicks each. Half of the chickens fed on each diet were injected intraperitoneally with 0.5 g/kg body weight of LPS at 16,18 and 20 day of age, the remaining chickens were injected with the same amount of a saline as the LPS injected group. The experimental period was 21d. The results showed that:(1) LPS challenge significantly reduced the growth performance of chickens (P<0.05). Dietary sodium butyrate attenuated the decrease of growth performance (P<0.05). In addition, LPS injection significantly increased the levels of IL-1β, IL-6, TNF-α, CORT、α1-acid glycoprotein (AGP), glucagons (PG) and total protein (P<0.01), and decreased the levels of insulin (Ins), glucose and triglycerides (P<0.05) in serum of broiler chickens both at 21 and 42 day of age. On day 20, it’s obvious that sodium butyrate inhibited the increase of the level of TNF-α, AGP, Ins, PG, glucose and total protein (P<0.05). Meanwhile, there was interaction (P<0.05) between dietary sodium butyrate and LPS on the CS on day 16 and AGP, glucose and total protein on day 20 (P<0.05).(2) The treatment of LPS significantly decreased the villus height and the V/C value and increased the crypt depth in duodenum. Meanwhile, the villus height and crypt depth of duodenum and jejunum treated with sodium butyrate shown significantly increased, and same increase trend was seen on the V/C value in chickens, In addition, LPS injection obviously increased the contents of myeloperoxidase (MPO), intercellular adhesion molecule-1 (ICAM-1) and activated NF-κB in mucosa of duodenum and jejunum, and significantly increased the mRNA expressions of IL-1β, IL-6 and TNF-a in the mucosa of duodenum (P<0.05). In contrast, the level of insulin like growth factor 1 (IGF-1) was decreased in the duodenum and jejunum mucosa (P<0.05). Meanwhile, the contents of MPO, activated NF-κB and mRNA expressions of TNF-αin duodenum mucosa and the activated NF-κB contents in jejunum mucosa were notable decreased when treated with sodium butyrate, while attenuated the adverse effects of the treatment of LPS (P<0.05). Additionally, there were interactions between dietary sodium butyrate and LPS on MPO and ICAM-1 in duodenum (P<0.05).3. The third study was to investigate the effects of microencapsulated sodium butyrate and oxidative injury induced by dietary CORT on intestinal antioxidant function and apoptosis of broiler chickens and to explore the action. A total of 120 1-d-old AA broiler chicks were randomly allocated to 2 treatment groups and were fed on a control diet or 0.4 g/kg microencapsulated sodium butyrate diet. Each treatment had 6 replicates with 5 chicks each. From 7 d of age onwards,50%of the chickens in each dietary treatment were subjected to CORT treatment (30 mg/kg of diet). The experimental period was 21d. The results showed that the dietary CORT very significantly decreased F1 and BWG and increased F/G of broiler chickens (P<0.001). Meanwhile, the dietary microencapsulated sodium butyrate markedly decreased F/G and attenuated the BWG decrease induced by CORT treatment (P<0.05).In addition, there was an interaction between microencapsulated sodium butyrate and CORT on F/G (P<0.05). Moreover, CORT supplementation significantly decreased the activities of SOD, GSH-Px, CAT in duodenum mucosa and the activities of SOD and CAT in jejunum mucosa (P<0.01); meanwhile, great lower level MDA in the mucosa of duodenum and jejunum was also observed. In contrast, the treatment of microencapsulated sodium butyrate markedly increased the CAT activity in duodenum and jejunum mucosa and decreased the MDA level in duodenum mucosa (P< 0.01). Higher apoptosis index (AI) and lower mRNA expressions of Bcl-2 in duodenum mucosa were also induced by dietary CORT (P<0.05). Meanwhile, microencapsulated sodium butyrate decreased the AI and increased the expression of Bcl-2 in duodenum mucosa (P<0.05).4. The fourth study was to investigate the effects of dietary microencapsulated sodium butyrate and acute pre-slaughter stress mimiced by 1 single s.c. CORT administration on body weight, carcass characteristics, muscle antioxidant status and meat quality of broiler chickens. A total of 120 1-d-old male healthy AA broiler chickens were also allotted into a 2x2 factorial arrangement with microencapsulated sodium butyrate levels (0 g/kg or 0.4 g/kg microencapsulated sodium butyrate diet) and challenge status (4 mg/kg BW CORT in corn oil or the same amount of corn oil) as main factor. Feeding period was 42d and the experimental period was 3h before slaughter. The results showed that the BW of the CORT challenged groups lost much more than the sham control groups (P<0.001), whereas it was alleviated by the dietary microencapsulated sodium butyrate (P<0.05). Meanwhile, the CAT activity was decreased and MDA level was increased by CORT injection (P< 0.05), and dietary microencapsulated sodium butyrate significantly inhibited this effect (P< 0.05). In addition, lower pH values and higher b* values were also observed in CORT-challenged chickens (P<0.05), and microencapsulated sodium butyrate partially exert a preventive effect. Microencapsulated sodium butyrate extremely decreased the contents of saturated fatty acids (SFA) and C18:0, increased C20:0 and C20:4 contents (P< 0.01), and increased the the ratio of PUFA and SFA and the ratio of unsaturated fatty acids and SFA (P<0.05). However, the effect of CORT administration on fatty acid composition was not significant (P>0.05). As stated above, the conclusions are as follows:(1) Diets supplemented with sodium butyrate at the level of 0.25 to 1.00 g/kg had no significant effect on the growth performance of normally raised broiler chickens, but could maintain its health through regulating immune response and improve antioxidant function, and the level of 1.00 g/kg had the best effect.(2) LPS challenge significantly induced the nutritional costs and reduced the growth performance of chickens; meanwhile increased the level of activated NF-κB and the mRNA expression of pro-inflammatory cytokines in intestinal mucosa, which promoted intestinal mucosal immune response and finally affected the intestinal development.1.00 g/kg dietary sodium butyrate obviously alleviated the immune response caused by LPS injection, improved the intestinal structure and function and maintained the growth performance in broiler chickens, which may correlate positively with the inhibition of NF-κB pathway activation by sodium butyrate.(3) Dietary CORT markedly decreased the intestinal antioxidant function, enhanced intestinal epithelial cells apoptosis and reduced mucosa mRNA expressions of Bcl-2. Meanwhile, dietary microencapsulated sodium butyrate promoted the antioxidant function, inhibited the apoptosis and increased the mRNA expressions of Bcl-2 in intestinal mucosa, which probably beneficial to the intestinal development in broiler chickens.(4) The acute preslaughter stress mimiced by exogenous CORT exposure could significantly increase the BW loss, induce oxidative stress and further decrease meat quality. Meanwhile, dietary microencapsulated sodium butyrate partially attenuated the negative effect caused by CORT injection. Especially, there was a positive effect of sodium butyrate on the fatty acid composition in the breast meat of broiler chickens.