Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Xiaolun Sun

Committee Member

Billy Hargis

Second Committee Member

Adnan Alrubaye

Third Committee Member

Young Min Kwon

Fourth Committee Member

Joshua Lyte

Keywords

Bile acid, Host response, Microbiota metabolites, mTOR, Necrotic enteritis, rapamycin

Abstract

Necrotic enteritis (NE), caused by C. perfringens and coccidiosis, is responsible for substantial economic loss annually. In the first chapter, we investigated the effect of secondary bile acid on necrotic enteritis. Day-old broiler chicks were randomly assigned to 5 groups of diets supplemented with 0 (basal diet), 0.8, 1.0, and 1.5 g/kg (on top of basal diet) deoxycholic acid (DCA). The birds were challenged with Eimeria maxima (20,000 oocysts/bird) at d 18 and C. perfringens (109CFU/bird/day) at d 23 and d 24 to induce NE. Birds were sacrificed at d 26, and ileal tissue and digesta samples were collected. DCA alleviated the subclinical NE-induced intestinal inflammation compared to NE control birds. NE infection has significantly reduced overall bile acids in ileum content (7,638 vs. 2,530 nmol/g digesta). At the molecular level, the highest DCA dose at 1.5 g/kg reduced C. perfringens luminal colonization compared to NE birds using PCR and FISH assay.

In the second chapter, we investigated if the NE severity would be reduced by restoring total bile acids. Day-old broiler chicks were randomly assigned to 6 groups: non-infected (non-challenged) group, NE challenged group; NE challenged group treated 1.5% commercial bile (CMB), 1.5% deoxycholic acid (DCA), 1.5% lithocholic acid (LCA), or 3.2g/kg of chicken bile (CB) starting from d14-25. The birds were challenged with E. maxima (15,000 oocysts/bird) at d 18 and C. perfringens (109 CFU/bird) at d 23 and d 24 to induce NE. Birds were euthanized at d 25, and ileal tissue and digesta samples were collected. Both commercial bile and chicken bile failed to attenuate body weight gain loss compared to NE, respectively. Interestingly, DCA at 1.5 g/kg in feed alleviated the NE-induced BWG loss compared to NE birds. C. perfringens colonization was decreased significantly in the DCA group (5.31 vs. 6.36 logs, P = 0.04) compared to NE infected group. In the third chapter, we investigated if blocking mTOR can modulate the NE induced intestinal inflammation. It has been established that the mammalian target of Rapamycin (mTOR) inhibitors has anti-inflammatory effects in models of experimental colitis. However, its impact on necrotic enteritis induced intestinal inflammation still not mostly unknown. We find only rapamycin either subcutaneous or in-feed treatment attenuated necrotic enteritis induced histology score in both subclinical and clinical NE disease. However, only rapamycin treatment is inefficient in preventing body weight loss caused by clinical necrotic enteritis. And rapamycin with DCA treatment attenuates necrotic enteritis induced body weight loss, histology score, and overall health of birds. Rapamycin, DCA, and rapamycin with DCA decreased expression of genes encoding the proinflammatory cytokines interferon-γ, interleukin (Il)-23, and 22 Further mechanistic studies corroborate the in-vivo experiment findings show that direct rapamycin and DCA and their combination reduces the immune cells migration and NE induced immune cells infiltration.

The results suggest that DCA reduced the C. perfringens colonization in NE and that blocking mTOR signaling decreased NE induced inflammation by blocking immune cells infiltration in NE infected birds.

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